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A faunal inventory of methane seeps on the Pacific margin of Costa Rica
expand article infoCharlotte A. Seid, Avery S. Hiley, Marina F. McCowin, José I. Carvajal, Harim Cha, Shane T. Ahyong§|, Oliver S. Ashford, Odalisca Breedy#, Douglas J. Eernisse¤, Shana K. Goffredi«, Michel E. Hendrickx», Kevin M. Kocot˄, Christopher L. Mah˅, Allison K. Miller¦, Nicolás Mongiardino Koch, Rich Mooiˀ, Timothy D. O'Haraˁ, Fredrik Pleijel, Josefin Stiller, Ekin Tilic, Paul Valentich-Scott, Anders Warén, Mary K. Wicksten, Nerida G. Wilson, Erik E. Cordes, Lisa A. Levin, Jorge Cortés#, Greg W. Rouse
‡ University of California San Diego, La Jolla, United States of America
§ Australian Museum, Sydney, Australia
| University of New South Wales, Kensington, Australia
¶ Ocean Program, World Resources Institute, London, United Kingdom
# University of Costa Rica, San José, Costa Rica
¤ California State University Fullerton, Fullerton, United States of America
« Occidental College, Los Angeles, United States of America
» Universidad Nacional Autónoma de México, Mazatlán, Mexico
˄ University of Alabama, Tuscaloosa, United States of America
˅ Smithsonian National Museum of Natural History, Washington, United States of America
¦ University of Otago, Dunedin, New Zealand
ˀ California Academy of Sciences, San Francisco, United States of America
ˁ Museums Victoria, Melbourne, Australia
₵ University of Gothenburg, Gothenburg, Sweden
ℓ University of Copenhagen, Copenhagen, Denmark
₰ Senckenberg Research Institute and Natural History Museum, Frankfurt, Germany
₱ Santa Barbara Museum of Natural History, Santa Barbara, United States of America
₳ Swedish Museum of Natural History, Stockholm, Sweden
₴ Texas A&M University, Texas, United States of America
₣ University of Western Australia, Perth, Australia
₮ Western Australian Museum, Welshpool, Australia
₦ Temple University, Philadelphia, United States of America
Open Access

Abstract

The methane seeps on the Pacific margin of Costa Rica support extensive animal diversity and offer insights into deep-sea biogeography. During five expeditions between 2009 and 2019, we conducted intensive faunal sampling via 63 submersible dives to 11 localities at depths of 300–3600 m. Based on these expeditions and published literature, we compiled voucher specimens, images, and 274 newly published DNA sequences to present a taxonomic inventory of macrofaunal and megafaunal diversity with a focus on invertebrates. In total 488 morphospecies were identified, representing the highest number of distinct morphospecies published from a single seep or vent region to date. Of these, 131 are described species, at least 58 are undescribed species, and the remainder include some degree of taxonomic uncertainty, likely representing additional undescribed species. Of the described species, 38 are known only from the Costa Rica seeps and their vicinity. Fifteen range extensions are also reported for species known from Mexico, the Galápagos seamounts, Chile, and the western Pacific; as well as 16 new depth records and three new seep records for species known to occur at vents or organic falls. No single evolutionary narrative explains the patterns of biodiversity at these seeps, as even morphologically indistinguishable species can show different biogeographic affinities, biogeographic ranges, or depth ranges. The value of careful molecular taxonomy and comprehensive specimen-based regional inventories is emphasized for biodiversity research and monitoring.

Key words

Biodiversity, biogeography, Central America, chemosynthetic ecosystem, COI, deep sea, DNA ‘barcodes’, molecular taxonomy, review

Introduction

The Costa Rica margin (CRM) occupies a central position in the biogeographic and tectonic landscape of the eastern Pacific. The subduction of the Cocos Plate beneath the Caribbean Plate at the Middle America Trench gives rise to deep-sea methane seeps (hereafter called “seeps”) (Kahn et al. 1996; McAdoo et al. 1996; Zuleger et al. 1996), as are found on the neighboring continental margins from Oregon to Chile (Sibuet and Olu 1998; Van Dover et al. 2002; Levin et al. 2016). The boundaries of the Cocos Plate adjoin the hydrothermal vent fields of the East Pacific Rise and the Galápagos Rift, which also directly links to the CRM via the Coco Submarine Volcanic Range (Kimura et al. 1997; von Huene et al. 2000; Fiedler and Lavín 2006; Beaulieu et al. 2013). This geographic position suggests the potential for population connectivity to seeps north and south along the continental margins, to the tectonically adjacent vent fields, and to the central and western Pacific via deep-ocean equatorial circulation (Tunnicliffe et al. 1998; Van Dover et al. 2002; Bachraty et al. 2009; Miloslavich et al. 2011). Furthermore, the biogeographic history of the CRM has been influenced by the emergence of the Isthmus of Panama (Central American Isthmus) (Cortés and Wehrtmann 2009), from the closure of deep-water exchange to the western Atlantic approximately 9 million years ago to the formation of the land barrier ~ 2.8 million years ago (O’Dea et al. 2016). The faunal diversity of the CRM thus offers a range of insights into deep-sea biogeography and evolution.

Active seepage of methane-rich fluids occurs at more than 100 sites located ca 50 km offshore along the CRM, from southern Nicaragua to the Osa Peninsula (Kahn et al. 1996; McAdoo et al. 1996; Zuleger et al. 1996; Kimura et al. 1997; Bohrmann et al. 2002; Sahling et al. 2008). The seeps occur at depths of ~ 400–3800 m at diverse geological features including mounds, faults, seamount subduction scars, and landslides (Kahn et al. 1996; McAdoo et al. 1996; Bohrmann et al. 2002; Sahling et al. 2008). The sites studied in this work are shown in Fig. 1. The seeps also span hydrographic gradients. Between 400 and 1800 m, the temperature ranges from 9.5 to 2.7 °C and oxygen concentration ranges from 0.04 to 1.9 ml/l, with an oxygen minimum zone at 300–600 m (Bohrmann et al. 2002; Levin et al. 2015). Methane concentrations vary with depth and among sites across three orders of magnitude, from background levels of ~ 2 nmol/l to maximum levels of 75–1506 nmol/l (Bohrmann et al. 2002; Mau et al. 2014). These abiotic gradients invite careful comparisons of biodiversity across the ensemble of seep sites.

Figure 1. 

Map of the Costa Rica seep sites sampled in this study. Maps were generated using the R package marmap (Pante and Simon-Bouhet 2013) and bathymetric data from NOAA (https://www.ncei.noaa.gov/maps/autogrid/, accessed 25 August 2021).

The first submersible dives at the CRM in 1994 revealed biological indicators of chemosynthetic activity, namely the presence of authigenic carbonates, microbial mats, and symbiont-bearing invertebrate megafauna (Fig. 2A–E) (Kahn et al. 1996; McAdoo et al. 1996). Authigenic carbonates are precipitated via anaerobic oxidation of methane (Ritger et al. 1987), in which a consortium of methane-oxidizing (methanotrophic) archaea and sulfate-reducing bacteria generates bicarbonate and hydrogen sulfide (Boetius et al. 2000; Orphan et al. 2001). Hydrogen sulfide, in turn, supports chemosynthesis by sulfur-oxidizing (thiotrophic) microbes (Tunnicliffe et al. 2003). At the CRM seeps, thiotrophic bacteria constitute many of the microbial mats (Mau et al. 2006, 2014; Bailey et al. 2011; Bernardino et al. 2012; Niemann et al. 2013) and play an important role as nutritional symbionts of vestimentiferan tubeworms, bathymodiolin mussels, and vesicomyid clams (Mau et al. 2006; Brzechffa and Goffredi 2021). As at other seeps (Suess et al. 1985; Sibuet and Olu 1998), these large-bodied symbiont-bearing invertebrate groups tend to dominate the biomass, and much of the initial biological characterization of the CRM seeps focused on these conspicuous megafauna (Kahn et al. 1996; Peek et al. 2000; Bohrmann et al. 2002; Goffredi et al. 2003).

Figure 2. 

Diversity of habitats at the Costa Rica seeps. Credit: ROV SuBastian/Schmidt Ocean Institute A authigenic carbonates at Mound 12 (1006 m, Dive S0215) B microbial mat at Rio Bongo Scar (609 m, Dive S0219) C vestimentiferan tubeworm aggregation (predominantly Lamellibrachia barhami) at Jacó Scar (1814 m, Dive S0212) D mussels (Bathymodiolus nancyschneiderae) and yeti crabs (Kiwa puravida) on authigenic carbonates at Mound 12 (1006 m, Dive S0215) E vesicomyid clams at Jacó Scar (1781 m, Dive S0214) F seepage of higher-temperature fluid at the Jacó Scar hydrothermal seep site (1803 m, Dive S0214) G wood fall at Jacó Scar (1875 m, Dive S0214) H animal fall (billfish skull, utilized by Grimothea monodon squat lobsters) at Quepos Slide (403 m, Dive S0216).

The CRM seeps also harbor a variety of animals that do not directly depend on chemosynthetic symbionts for nutrition. Initial records of such non-obligate seep fauna included limpets, snails, crabs, galatheoids, crinoids, actiniarians, corals, ophiuroids, echinoids, holothuroids, sponges, and macrurid fish (Kahn et al. 1996; Bohrmann et al. 2002). Further sampling has revealed diverse macrofaunal assemblages associated with carbonates and sediments at different habitat types (e.g., Levin et al. 2012, 2015; Ashford et al. 2021b; Pereira et al. 2021). To date, 48 animal species have been described from the CRM seeps, including annelids (Aguado and Rouse 2011; Borda et al. 2013; Summers et al. 2014b; Watson et al. 2016; McCowin and Rouse 2018; Rouse et al. 2018; Lindgren et al. 2019; Hatch et al. 2020; Salazar-Vallejo 2020a; Yen and Rouse 2020; Rouse and Kupriyanova 2021; Pearson and Rouse 2022; Villalobos-Guerrero et al. 2024), corals (Opresko and Breedy 2010; Breedy et al. 2019), crustaceans (Thurber et al. 2011; Martin et al. 2018; Rodríguez-Flores et al. 2023), fish (Frable et al. 2023), echinoderms (Payne et al. 2023), mollusks (Barry and Kochevar 1999; Krylova and Sahling 2006; Martin and Goffredi 2012; Warén and Rouse 2016; McCowin et al. 2020), and nemerteans (Sagorny et al. 2022), as well as a ciliate (Pasulka et al. 2017) for a total of 49 eukaryotic species.

Furthermore, the CRM seeps show environmental and biological connections to other chemosynthesis-based habitats. The Jacó Scar “hydrothermal seep” site at 1800 m depth (Fig. 2F) appears to represent an intermediate environment between seeps and hydrothermal vents, as elevated water temperatures (up to 5.2 °C, representing nearly 3 °C above ambient) support certain vent-affiliated fauna (Levin et al. 2012). Wood falls (Fig. 2G) and animal carcasses (Fig. 2H) occur in the vicinity of these seeps, as might be expected from their proximity to a forested coast and its river discharges. Experimental deployments of wood and bone substrates have enabled further investigation of seep-adjacent organic fall communities (Hatch et al. 2020; Pereira et al. 2022; Payne et al. 2023). These intersectional habitats offer the opportunity to address questions of colonization, habitat suitability, and biogeography across different chemosynthesis-based ecosystems.

During five research cruises to the CRM in 2009–2019, we used deep submergence vehicles to conduct intensive faunal sampling. Based on these expeditions and published literature, we compiled voucher specimen records, images, and DNA sequences to present a taxonomic inventory of faunal diversity at these seeps. We report new range extensions and depth records, discuss connections to other chemosynthesis-based ecosystems, and assess biogeographic patterns.

Materials and methods

Sampling locations

Specimens were collected during five research cruises to the central CRM (Fig. 1): R/V Atlantis with DSV Alvin AT15-44 (2009), AT15-59 (2010), AT37-13 (2017), AT42-03 (2018); R/V Falkor with ROV SuBastian FK190106 (2019). Collection localities, depths, dates, and details are summarized in Table 1.

Table 1.

Submersible dives and collection events. AD = HOV Alvin, R/V Atlantis. S = ROV SuBastian, R/V Falkor. MC = multicore. Multicores and plankton tows were deployed from R/V Atlantis. Coordinates reflect dive summaries as reported in the HOV Alvin dive logs (https://ndsf.whoi.edu/data/) and the R/V Falkor FK190106 cruise report. Dates reflect local time. Depth ranges reflect the minimum and maximum depth for sample collection events. In most cases, more precise coordinates and depths for specific animals are available on the SIO-BIC online database (https://sioapps.ucsd.edu/collections/bi/).

Cruise Dive or deployment Locality Date Latitude, Longitude Depth, m
AT15-44 AD4501 Mound 12 2009-02-22 8.9300, -84.3135 984–997
AD4502 Mound 12 2009-02-23 8.9285, -84.3132 987–997
AD4503 Mound 12 2009-02-24 8.9308, -84.3072 967–995
AD4504 Mound 11 2009-02-25 8.9208, -84.3054 1004–1011
AD4505 Mound 11 2009-02-26 8.9198, -84.3055 1019–1025
AD4506 Parrita Seep 2009-02-27 8.9718, -84.6235 1030–1179
AD4507 Parrita Scar 2009-02-28 8.9353, -84.6465 1659–1667
AD4508 Parrita Seep 2009-03-01 9.0303, -84.6230 1401–1419
AD4509 Jacó Scar and Jacó Slope 2009-03-03 9.1172, -84.8425 974–1856
AD4510 Jacó Summit 2009-03-04 9.1723, -84.7987 741–744
AD4511 Mound 12 2009-03-05 8.9305, -84.3123 988–997
AD4512 Quepos Slide 2009-03-06 8.8536, -84.2181 344–411
AD4513 Jacó Scar 2009-03-07 9.1167, -84.8351 1744–1818
MC1-2 Transition site near Mound 12 (~ 500 m from active seep) 2009-02-21 8.9316, -84.3168 1019
AT15-59 AD4586 Mound 12 2010-01-07 8.9308, -84.3130 982–998
AD4587 Mound 12 2010-01-08 8.9306, -84.3123 990–996
AD4588 Mound 12 2010-01-09 8.9308, -84.3125 995–997
AD4589 Mound 12 2010-01-10 8.9298, -84.3121 997
AD4590 Jacó Scar 2010-01-11 9.1176, -84.8395 1791–1800
AD4591 Jacó Scar 2010-01-12 9.1182, -84.8391 1752–1795
MC1 Transition site near Mound 12 (~ 400 m from active seep) 2010-01-06 8.9325, -84.3158 995
MC4 Transition site near Mound 11 (~ 400 m from active seep) 2010-01-10 8.9208, -84.3016 1031
Plankton Tow 6 Jacó Summit 2010-01-12 9.1713, -84.7987 0–350 (350 m wire out)
AT37-13 AD4906 Mound 12 2017-05-21 8.9308, -84.3128 995–1002
AD4907 Mound 12 2017-05-22 8.9304, -84.3128 990–999
AD4908 Mound 12 2017-05-23 8.9304, -84.3126 989–1001
AD4909 Mound 12 2017-05-24 8.9305, -84.3125 967–1000
AD4910 Mound 12 2017-05-25 8.9304, -84.3126 988–1004
AD4911 Jacó Scar 2017-05-26 9.1151, -84.8468 1757–1892
AD4912 Jacó Scar 2017-05-27 9.1154, -84.8362 1795–1859
AD4913 Jacó Scar 2017-05-28 9.1156, -84.8401 1798–1908
AD4914 Jacó Scar 2017-05-29 9.1175, -84.8395 1632–1886
AD4915 Jacó Scar 2017-05-30 9.1180, -84.8404 1741–1885
AD4916 Jacó Scar 2017-05-31 9.1193, -84.8428 1604–1854
AD4917 Mound 12 2017-06-01 8.9293, -84.3150 965–1000
AD4918 Quepos Slide 2017-06-02 8.8535, -84.2177 333–408
AD4919 Quepos Slide 2017-06-03 8.8527, -84.2174 379–410
AD4921 Quepos Slide 2017-06-04 8.8532, -84.2155 345–394
AD4922 Mound 12 2017-06-05 8.9296, -84.3078 964–1009
AD4923 Parrita Seep 2017-06-06 8.9759, -84.6238 1037–1097
AD4924 Parrita Seep 2017-06-07 9.0305, -84.6202 1400–1410
AT42-03 AD4971 Jacó Scar 2018-10-17 9.1170, -84.8426 1746–1824
AD4972 Jacó Scar 2018-10-18 9.1164, -84.8403 1746–1845
AD4973 Jacó Scar 2018-10-19 9.1148, -84.8398 1784–1887
AD4974 Mound 12 2018-10-20 8.9297, -84.3078 990–1010
AD4975 Mound 12 2018-10-21 8.9310, -84.3075 988–1002
AD4976 Jacó Scar 2018-10-22 9.1139, -84.8401 1836–1887
AD4977 Jacó Scar 2018-10-23 9.1163, -84.8418 1783
AD4978 Mound 12 2018-10-24 8.9294, -84.3143 996–999
AT42-03 AD4979 Quepos Slide 2018-10-25 8.8539, -84.2178 380–397
AD4984 Mound 12 2018-10-30 8.9300, -84.3137 964–998
AD4985 Mound 12 2018-10-31 8.9303, -84.3129 991–1002
AD4986 Quepos Slide 2018-11-01 8.8540, -84.2195 308–379
AD4987 Mound 12 West 2018-11-02 8.9292, -84.3167 995–1012
AD4988 Mound 11 2018-11-03 8.9193, -84.3027 998–1025
AD4989 Jacó Scar 2018-11-04 9.1174, -84.8417 1758–1792
AD4990 Parrita Seep 2018-11-05 9.0321, -84.6197 1400–1435
FK190106 S0212 Jacó Scar 2019-01-06 9.1175, -84.8393 1780–1869
S0213 Jacó Summit 2019-01-06 9.1734, -84.8038 730–820
S0214 Jacó Scar 2019-01-07 9.1175, -84.8393 1780–1875
S0215 Mound 12 2019-01-08 8.9307, -84.3126 982–1016
S0216 Quepos Slide 2019-01-09 8.8539, -84.2193 275–404
S0217 The Thumb 2019-01-10 9.0486, -84.3945 940–1074
S0218 Parrita Scar 2019-01-11 8.9498, -84.6381 1110–1988
S0219 Rio Bongo Scar 2019-01-13 9.2862, -85.2757 480–661
S0220 Subduction Plume 2019-01-14 8.8785, -84.8695 3399–3601
S0230 Mound Jaguar 2019-01-25 9.6558, -85.8813 1895–2000

The submersible dives in this study primarily investigated areas of active methane seepage, as indicated by the presence of non-sedimented authigenic carbonates, microbial mats, or symbiont-bearing megafauna (Levin et al. 2015; Pasulka et al. 2017; Ashford et al. 2021b; Pereira et al. 2021). Certain dives also covered adjacent deep-sea habitat, as defined by the absence of these indicators, and “transition” habitat, characterized by partially sedimented authigenic carbonates, the remains of symbiont-bearing bivalves, and reduced density of seep-associated megafauna (Ashford et al. 2021b; Pereira et al. 2021). The complex biological and geochemical influences of seeps are thought to extend for hundreds of meters up to ~ 1 km in three dimensions (Levin et al. 2016; Ashford et al. 2021b), a spatial extent comparable to that covered by a given submersible dive in this study (typically a maximum radius of 1 km, centered at an active seep site). In a recent ecological study of the transition zone between seeps and adjacent deep-sea habitat at the CRM (Ashford et al. 2021b), the distances between accepted “active” and “transition” or “background” habitats ranged from 257–967 m. Therefore, all specimens collected on seep-focused dives and within ~ 500 m of active seepage were considered within the scope of this study, including a few opportunistically collected specimens from habitats that likely represent background or transition zones (e.g., three multicore deployments in Table 1). Non-seep habitats such as seamounts and Quepos Plateau (von Huene et al. 2000) were investigated during some of the same cruises but are outside the scope of this work.

We generally follow the locality names listed in Sahling et al. (2008). The locality named here as Parrita Seep has been variously cited as “Mound Quepos,” “Quepos Seep,” or “Quepos Seep at Parrita Scar” in previous work (e.g., Han et al. 2004; Sahling et al. 2008; Levin et al. 2015; McCowin and Rouse 2018). Based on the geological categorization of this site as a fault-controlled seep rather than a mound (Sahling et al. 2008) and its proximity to a separate site known as Parrita Scar, we follow other studies (McCowin et al. 2020; Rojas-Jimenez et al. 2020; Ashford et al. 2021b; Rouse and Kupriyanova 2021) in synonymizing these names as Parrita Seep.

Specimen collection and vouchering

Most specimens were collected during submersible dives using equipment such as hydraulic arms, suction samplers, scoops, push cores, a Bushmaster Jr. device for sampling tubeworm aggregations (Bergquist et al. 2002), and a customized mussel pot device for sampling mussel aggregations (Cordes et al. 2010). Some specimens were collected opportunistically during multicore deployments or plankton tows adjacent to the main study sites. Some specimens were collected from experimentally deployed substrates such as wood, bone, or carbonate rocks, including rocks experimentally transplanted across different zones at the same locality and similar depth (Pereira et al. 2022), but no animals were transplanted between localities. Associations with wood or bone are indicated in each taxonomic listing, and specimens were collected from naturally occurring seep substrates unless otherwise indicated.

Specimens were maintained alive in chilled seawater, treated with an appropriate relaxing agent, and processed following recommended practices for DNA taxonomy of marine invertebrates (Gemeinholzer et al. 2010; Templado et al. 2010; Glover et al. 2015; Rouse et al. 2022). Live specimens were photographed using a handheld camera (e.g., Canon EOS M5, Canon Rebel T1, Nikon D70, Panasonic DMC-TS4, Ricoh WG-4, Ricoh WG-50) or a photomicroscopy station (e.g., a Leica S8 Apo or MZ9.5 stereomicroscope with a camera attachment for a Canon EOS Rebel T3i, T6s, or T6i; EOS M5; or PowerShot G9). Tissue subsamples or small whole specimens were preserved in 95% ethanol for genetic analysis. Voucher specimens for morphological analysis were typically fixed in 10% seawater formalin for at least 24 h, rinsed with fresh water, and transferred to 50% ethanol for long-term archival. For certain taxa, e.g., echinoderms and crustaceans, large voucher specimens were instead treated with 95% ethanol in several washes for at least 24 h each and then transferred to 50% ethanol for long-term archival. Selected specimens or tissues were treated with RNAlater (Ambion, Austin, TX), paraformaldehyde, glutaraldehyde, or osmium tetroxide. Some specimens from the 2009 and 2010 cruises were treated with the glyoxal fixative Prefer (Anatech Ltd., Battle Creek, MI) for both molecular and morphological purposes, but other fixation-preservation strategies were found to be preferable.

Specimens were deposited in the Scripps Institution of Oceanography Benthic Invertebrate Collection (SIO-BIC) and the Museo de Zoología, Universidad de Costa Rica (MZUCR, invertebrate collections; UCR, fish collection).

Taxonomic scope

We targeted benthic invertebrate macrofauna (retained on a 300 µm mesh and typically > 1 mm in size) and megafauna due to the nature of our sampling gear, although a few opportunistically collected exceptions such as large nematodes are reported. The meiofaunal (Neira et al. 2018; Gracia C et al. 2020), fungal (Rojas-Jimenez et al. 2020), and microbial communities of the Costa Rica seeps (Bailey et al. 2011; Niemann et al. 2013; Tavormina et al. 2013; Dekas et al. 2014; Case et al. 2015; Pasulka et al. 2017; Brzechffa and Goffredi 2021; Metcalfe et al. 2021) have been explored in other studies. Our sampling was not intended to be quantitative, as related investigations have explored macrofaunal species richness, biomass, density, and other ecological metrics at these seeps (Levin et al. 2012, 2015; Ashford et al. 2021b, 2021a; Pereira et al. 2021, 2022).

We reported only taxa that were linked to physical specimens, given the importance of museum vouchers for genetic characterization, species descriptions, scientific reproducibility, and the principles of Findable, Accessible, Interoperable, and Reusable (FAIR) research (Howell et al. 2020). Nonetheless, these expeditions also captured images and video of additional fauna (e.g., medusae, cephalopods, and fishes) that were not collected and that may form the basis of future studies.

Specimen identification

Following preliminary morphological identification during shipboard processing, specimens were identified to the lowest possible taxonomic level based on genetics and/or morphology. Genetic identification was facilitated by querying sequences against the NCBI GenBank database (Clark et al. 2016) using the nucleotide BLAST (blastn) suite (https://blast.ncbi.nlm.nih.gov/) (Zhang et al. 2000; Boratyn et al. 2013). Biogeography assessments and access to taxonomic literature were facilitated by the Global Biodiversity Information Facility (GBIF) (GBIF: The Global Biodiversity Information Facility 2024) and the Biodiversity Heritage Library (Gwinn and Rinaldo 2009).

Taxonomic uncertainty was expressed using recommended terminology and practices for open nomenclature (Sigovini et al. 2016; Horton et al. 2021). For example, the abbreviation “stet.” (stetit) is used to indicate that further identification to a lower taxonomic level was not attempted given the limitations of the specimen or of available taxonomic resources. Uncertainty at a given taxonomic level is indicated by the abbreviation “inc.” (incerta, incertus, incertum). Undescribed species that have been identified with certainty as new to science but have not yet been formally described or referenced in the literature, are notated with a unique alphanumeric code linked to a museum voucher, e.g., “sp. SIO_BIC_A00001” as opposed to a potentially non-unique designation such as “sp. 1”. Some morphospecies are also notated with unique voucher-linked alphanumeric codes, when multiple morphospecies must be distinguished from one another but cannot be matched with certainty to known species.

DNA extraction and sequencing

Genomic DNA was extracted following the manufacturer’s protocol for commercial kits such as the DNeasy Tissue Kit (Qiagen); the EZNA Micro-Elute Genomic DNA Kit (Omega Bio-Tek); or the Quick-DNA Miniprep, Microprep Plus, or 96 Plus Kit (Zymo Research, Irvine, CA and Tustin, CA). Polymerase chain reaction (PCR) amplification of phylogenetically informative gene fragments was performed using the primer pairs summarized in Table 2. A typical PCR included 1 μl of each primer (10 μM), 2 μl of genomic DNA, and the appropriate concentration of a commercially available reagents such as Apex 2.0x Taq Red DNA Polymerase Master Mix (Genesee Scientific), Hot Start Taq PCR Master Mix 2X (VWR), or Conquest PCR Master Mix (Lamda Biotech, St. Louis, MO). PCR products were purified with ExoSAP-IT (USB Corporation, Cleveland, OH) or the EZNA Cycle Pure Kit (Omega Bio-Tek). Sanger sequencing was performed by Eurofins Genomics (Louisville, KY), GeneWiz (South Plainfield, NJ), or Retrogen, Inc. (San Diego, CA). Consensus sequences were assembled using Geneious (https://www.geneious.com).

Table 2.

PCR primers and temperature profiles. Mitochondrial genes: COI = cytochrome c oxidase subunit I; COIII = cytochrome c oxidase subunit III; 16S = ribosomal RNA 16S subunit. Nuclear genes: 18S = ribosomal RNA 18S subunit.

Amplified gene fragment Primer pair References for primer sequences Temperature profile Taxa
COI LCO1490/ HCO2198 Folmer et al. 1994 94 °C/180s – (94 °C/30s – 47 °C/45s – 72 °C/60s) * 5 cycles – (94 °C/30s – 52 °C/45s – 72 °C/60s) * 30 cycles – 72 °C/300s Annelida, Arthropoda, Mollusca, Nemertea
COI dgLCO/ dgHCO Meyer 2003 95 °C/120s – (95 °C/40s – 45 °C/40s – 72 °C/60s) * 35 cycles – 72 °C/420s or 95 °C/300s – (95 °C/30s – 48 °C/30s – 72 °C/45s) * 35 cycles – 72 °C/300s Annelida, Mollusca, Holothuroidea, Caridea
COI PolyLCO/ PolyHCO Carr et al. 2011 95 °C/180 s – (95 °C/40 s – 42 °C/40 s – 72 °C/50 s) * 40 cycles – 72 °C/300 s Annelida
COI HCO2198/LCO_Apl Folmer et al. 1994; Bergmeier et al. 2019 95 °C/60s – (95 °C/20s – 52 °C/15s – 72 °C/30s) * 40 cycles – 72 °C/420s Aplacophora
COI HCO2198/ CrustF2 Costa et al. 2007 95 °C/60s – (95 °C/30s – 42 °C/90s – 72 °C/60s) *35 cycles – 72 °C/300s Arthropoda
COI COIceF/ COIceR Hoareau and Boissin 2010 95 °C/180s – (94 °C/45s – 48 °C/70s – 72 °C/80s) * 40 cycles – 72 °C/600s Echinodermata
COI ECOLa/ HCO2198 Folmer et al. 1994; Knott and Wray 2000 combined as in Deagle et al. 2003 94 °C/240s – (94 °C/30s – 50 °C/30s – 72 °C/45s) * 35 cycles – 72 °C/300s Asteroidea
COI Fsco1/ Co13r Helgen and Rouse 2006 94 °C/180s – (94 °C/45s – 48 °C/45s – 72 °C/60s) * 35 cycles – 72 °C/480s Crinoidea
COI COIef/ COIer Arndt et al. 1996 95 °C/120s – (95 °C/30s – 48 °C/30s – 72 °C/45s) * 35 cycles – 72 °C/600s Holothuroidea, Echinoidea
COI VesLCO/ VesHCO Peek et al. 1997 94 °C/240s – (94 °C/40s – 40 °C/40s – 72 °C/60 s) * 40 cycles – 72 °C/600 s Vesicomyidae
COI jgLCO1490/ jgHCO2198 Geller et al. 2013 95 °C/300s – (95 °C/30s – 48 °C/30s – 72 °C/45s) * 35 cycles – 72 °C/300s Hyalogyrina
COIII COIIIF/ COIIIR Geller and Walton 2001 95 °C/120s – (95 °C/30s – 45 °C/30s – 72 °C/60s) * 30 cycles – 72 °C/300s Actiniaria
16S 16SarL/ 16SbrH Palumbi 1996; Palumbi et al. 2002 95 °C/180s – (95 °C/40s – 50 °C/40s – 68 °C/50 s) * 35 cycles – 68 °C/300 s or 95 °C/180s – (95 °C/40s – 50 °C/40s – 72 °C/50 s) * 40 cycles – 72 °C/300 s Annelida, Nemertea, Holothuroidea, Polyplacophora, Paracrangon areolata, Grimothea monodon
16S ANEM16SA/ ANEM16SB Geller and Walton 2001 95 °C/120s – (95 °C/30s – 60 °C/30s – 72 °C/60s) * 30 cycles – 72 °C/300s Anthozoa
16S 16S_arL_solenos (CGACTGTTTAACAAAAACATTGCTC)/ 16S_brH_solenos (CCGATTTGAACTCAGATCATGTAG) this work (K. Kocot) 95 °C/60s – (95 °C/20s – 52 °C/15s – 72 °C/30s) *40 cycles – 72 °C/420s Aplacophora
16S AnnF/ 16Sb Edgecombe et al. 2002; Sjölin et al. 2005 combined as in Stiller et al. 2013 94 °C/120s – (94 °C/40s – 60 °C/40s – 70 °C/45s) * 35 cycles – 72 °C/420s Sabellidae, Macellicephalinae
18S Three overlapping fragments: 1F/5R, 3F/bi, a2.0/9R Giribet et al. 1996, 1999 combined as in Stiller et al. 2013 1F/5R: 95 °C/180s – (95 °C/60s – 49 °C/30s – 72 °C/90s) * 40 cycles – 72 °C/480s; 3F/bi: 95 °C/180s – (95 °C/30s – 52 °C/30s – 72 °C/90s) *40 cycles – 72 °C/480s; a2.0/9R: 95 °C/180s – (95 °C/30s – 49 °C/30s – 72 °C/90s) *40 cycles – 72 °C/480s Sabellidae
18S Three overlapping fragments: TimA/1100R2, 3F/bi, a2.0/9R Giribet et al. 1996, 1999; Norén and Jondelius 1999 combined as in Stiller et al. 2013 TimA/1100R2: 94 °C/180s – (94 °C/30s – 53 °C/45s – 72 °C/120s) * 40 cycles – 72 °C/300s; 3F/bi, a2.0/9R: see previous Sabellidae
18S Sol18F/ Sol18R Neulinger et al. 2006 94 °C/300s – (91 °C/40s – 50 °C/40s – 72 °C/90s) * 40 cycles – 72 °C/300s Solemyidae

Haplotype networks

Sequences were aligned using the MAFFT online service v. 7.471, option L-INS-I (Katoh et al. 2018). Haplotype networks were created with PopART v. 1.7 (Leigh and Bryant 2015) using the TCS algorithm (Clement et al. 2002).

Scanning electron microscopy (SEM)

Selected aplacophoran specimens were dried and mounted on stubs without critical point drying or sputter coating. Specimens were imaged on a Phenom Pro SEM.

Permits

Specimen collection and field operations were performed under the following permits issued by CONAGEBIO (Comisión Nacional para la Gestión de la Biodiversidad), INCOPESCA (Instituto Costarricense de Pesca y Acuicultura), and SINAC (Sistema Nacional de Áreas de Conservación) under MINAE (Ministerio de Ambiente y Energía), Government of Costa Rica: INCOPESCA-CPI-003-12-2018, R-070-2018-OT-CONAGEBIO, SINAC-CUSBSE-PI-R-032-2018, SINAC-SE-CUS-PI-R-035-2017. In accordance with the Nagoya Protocol on Access and Benefit Sharing, DNA sequencing for this project was authorized by the Contract for the Grant of Prior Informed Consent between MINAE-SINAC-ACMC and Jorge Cortés-Nuñez for the Basic Research Project: “FK190106-Cuantificación de los vínculos biológicos, químicos y físicos entre las comunidades quimiosintéticas con el mar profundo circundante.”

Taxonomic listing

For each taxonomic entry, we summarize the known localities and depths of occurrences at the CRM seeps, incorporating both published references and additional material examined in this work. Representative voucher specimens and their associated DNA sequences are listed by dive/deployment number (details in Table 1). Catalog numbers indicate a morphological voucher linked to a tissue sample suitable for genetic analysis, unless otherwise noted. For some groups such as octocorals, morphological vouchers and genetic tissue samples were deposited with separate institutions according to local expertise.

We also summarize the known localities and depths of occurrences beyond the CRM seeps. We indicate new biogeographic records, new depth records (defined here as at least 100 m from a previously reported minimum or maximum depth), and new seep records of species previously associated with vents or organic falls. Exact collection depths are provided where possible; approximations are indicated by ~ .

References indicate previously published records from the CRM seeps. Original species descriptions are indicated by **. References generally include voucher specimen listings with representative images and DNA sequences; where possible, we provide any missing components. Specimen catalog numbers pertain to SIO-BIC unless otherwise indicated. GenBank numbers refer to COI sequences unless otherwise indicated. New sequences are shown in bold.

For higher-level taxonomy, we follow the World Register of Marine Species (WoRMS Editorial Board 2024) or taxon-specific references. We notate higher classification according to the recommended best practice for the DarwinCore term higherClassification (Darwin Core Maintenance Group 2021), with full taxonomic authorities and Linnaean ranks available in the applicable references. Our ordering of major animal groups reflects the phylogeny in Dunn et al. (2014). Entries are listed alphabetically within each category.

Annelida

We list entries following the taxonomic arrangement in Rouse et al. (2022).

Annelida | Polychaeta | Errantia | Protodriliformia

Protodrilidae stet.

Fig. 3A

Figure 3. 

Annelida: Protodrilidae and Polynoidae, representative live images A Protodrilidae stet. (A8456) B Bathykurila sp. A sec. Glover et al. 2005 (A10050, dorsal view) C Bathykurila sp. A sec. Glover et al. 2005 (A10050, ventral view) D Branchinotogluma sp. SIO_BIC_A8265 (A8265, dorsal view) E Branchinotogluma sp. SIO_BIC_A8265 (A8265, ventral view) F Branchinotogluma sp. SIO_BIC_A8460 (A8460 and A16362, dorsal view) G Branchinotogluma sp. SIO_BIC_A8460 (A8460 and A16362, ventral view) H Branchinotogluma sp. SIO_BIC_A8460 (A8461, dorsal view). Scale bars: 1 mm.

Material examined. AD4906: A8261; AD4923: A8456 (PQ449314).

Localities. Mound 12 (1002 m), Parrita Seep (~ 1040–1101 m).

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Aphroditiformia | Polynoidae

Bathykurila sp. A sec. Glover et al. 2005

Fig. 3B, C

Material examined. AD4906: A8264; S0213: A10050 (PQ449253); S0217: A10086.

Localities. Jacó Summit (~ 730–820 m), Mound 12 (~ 997–1002 m), Mound 11 (1004–1040 m), The Thumb (1072 m).

Remarks. COI sequences of this morphospecies were > 99.42% identical to those of Bathykurila haplotype group A (GenBank DQ074778.1, DQ074779.1, DQ074780.1), which morphologically resembles B. guaymasensis Pettibone, 1989 as discussed in Glover et al. (2005).

Branchinotogluma sp. SIO_BIC_A8265

Fig. 3D, E

Material examined. AD4907: A8265 (OR682087).

Localities. Mound 12 (~ 990–999 m).

Remarks. An undescribed species. Specimen A8265 was associated with experimentally deployed wood.

Branchinotogluma sp. SIO_BIC_A8460

Fig. 3F–H

Material examined. AD4913: A13252 (OR682108); AD4924: A8460 (OR682111), A8461, A16362; S0218: A10190 (OR682109).

Localities. Parrita Scar (1364 m), Parrita Seep (~ 1400–1410 m), Jacó Scar (1847 m).

Remarks. An undescribed species.

Branchinotogluma sp. SIO_BIC_A9682

Fig. 4A–C

Figure 4. 

Annelida: Polynoidae, representative images. Live specimens are depicted unless otherwise specified A Branchinotogluma sp. SIO_BIC_A9682 (A9682, dorsal view) B Branchinotogluma sp. SIO_BIC_A9682 (A9682, ventral view) C Branchinotogluma sp. SIO_BIC_A9682 (A9763, dorsal view without scales) D Branchipolynoe eliseae (A6660, preserved specimen, dorsal and ventral views) E Branchipolynoe halliseyae (A1322, dorsal and ventral views) F Branchipolynoe kajsae (A6611, dorsal and ventral views) G Branchipolynoe meridae (A6616, dorsal and ventral views) H Gorgoniapolynoe cf. caeciliae (A8485, with host coralliid Co2947). Scale bars: 1 mm (A–C, H); 1 cm (D–G).

Material examined. AD4505: A1363 (OR682006); AD4924: A8459 (OR682020); AD4972: A9682 (OR682056); AD4978: A9763 (OR682070); S0230: A10185 (OR682045), A10187 (OR682037).

Localities. Mound 12 (~ 1000 m), Mound 11 (1025 m), Parrita Seep (~ 1400 m), Jacó Scar (~ 1800 m), Mound Jaguar (1908–1909 m).

Remarks. An undescribed species.

Branchipolynoe eliseae Lindgren, Hatch, Hourdez, Seid & Rouse, 2019

Fig. 4D

Reference. Lindgren et al. 2019**.

Localities. Mound 12 (997 m; type locality), Jacó Scar (~ 1752–1800 m).

Distribution. Known only from the CRM seeps.

Remarks. Symbiont of the mussels Bathymodiolus billschneideri and Ba. nancyschneiderae (Lindgren et al. 2019), typically with one adult worm and sometimes several very small juvenile worms per mussel. Possibly also found in Ba. earlougheri, whose locality and depth ranges overlap with the two known host mussel species (McCowin et al. 2020). The absence of B. eliseae occurrences in Ba. earlougheri is likely an artefact of limited sample size (Lindgren et al. 2019).

Branchipolynoe halliseyae Lindgren, Hatch, Hourdez, Seid & Rouse, 2019

Fig. 4E

Reference. Lindgren et al. 2019**.

Localities. Mound 12 (~ 1000 m; type locality), Parrita Seep (~ 1400 m), Jacó Scar (1758–1811 m).

Distribution. Known only from the CRM seeps.

Remarks. Symbiont of the mussels Bathymodiolus billschneideri, Ba. nancyschneiderae, and Ba. earlougheri (Lindgren et al. 2019), typically with one adult worm and sometimes several very small juvenile worms per mussel.

Branchipolynoe kajsae Lindgren, Hatch, Hourdez, Seid & Rouse, 2019

Fig. 4F

Reference. Lindgren et al. 2019**.

Localities. Mound 12 (~ 1000 m; type locality), Parrita Seep (~ 1400 m), Jacó Scar (~ 1800 m).

Distribution. Known only from the CRM seeps.

Remarks. Symbiont of the mussels Bathymodiolus billschneideri, Ba. nancyschneiderae, and Ba. earlougheri (Lindgren et al. 2019), typically with one adult worm and sometimes several very small juvenile worms per mussel.

Branchipolynoe meridae Lindgren, Hatch, Hourdez, Seid & Rouse, 2019

Fig. 4G

Reference. Lindgren et al. 2019**.

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m; type locality).

Distribution. Known only from the CRM seeps.

Remarks. Symbiont of the mussels Bathymodiolus billschneideri and Ba. earlougheri (Lindgren et al. 2019), typically with one adult worm and sometimes several very small juvenile worms per mussel. Possibly also found in Ba. nancyschneiderae, which co-occurs with Ba. earlougheri at Mound 12 (McCowin et al. 2020). The absence of B. eliseae occurrences in Ba. nancyschneiderae is likely an artefact of limited sample size (Lindgren et al. 2019).

Gorgoniapolynoe cf. caeciliae (Fauvel, 1913)

Figs 4H, 5A

Figure 5. 

Annelida: Polynoidae, representative images. Live specimens are depicted unless otherwise specified A Gorgoniapolynoe cf. caeciliae (A8485, removed from host Co2947) B Macellicephala sp. SIO_BIC_A8368 (A8368, preserved specimen) C Macellicephala sp. SIO_BIC_A9775 (A9775) D Macellicephala sp. SIO_BIC_A10055 (A10055, dorsal view) E Macellicephala sp. SIO_BIC_A10055 (A10055, ventral view) F Macellicephala sp. SIO_BIC_A10094 (A10094, dorsal view) G Macellicephala sp. SIO_BIC_A10094 (A10094, ventral view) H Macellicephala sp. SIO_BIC_A10099 (A10099, in situ on host cladorhizid sponge P1754). Credit: ROV SuBastian/Schmidt Ocean Institute. Scale bars: 1 mm (A, B, D–G); 1 cm (C).

Material examined. AD4506: A1549; AD4923: A8455 (PQ449313), A8485.

Localities. Parrita Seep (~ 1030–1094 m).

Remarks. Associated with coralliid octocorals: A1549 with coral Co2271, A8455 and A8485 with coral Co2947. The COI sequence of A8455 was 98.20% identical to a reference sequence of Gorgoniapolynoe cf. caeciliae molecular operational taxonomic unit (MOTU) 1 from the central Atlantic (ON479554.1), representing one of two lineages in a potential cryptic species complex with inter-lineage COI distances of 2–7% (Maxwell et al. 2022). The CRM specimens warrant further detailed comparison to these Atlantic G. cf. caeciliae lineages as well as to the eastern Pacific species G. guadalupensis Pettibone, 1991, which currently has no available reference sequences. Gorgoniapolynoe guadalupensis was originally described in association with Hemicorallium imperiale (Bayer, 1955) off Guadelupe Island, western Mexico, 1000–2000 m, and has been recorded from seamounts in the eastern Pacific (Fieberling Guyot, off southern California) and central Pacific (Markus Nekar Chain, west of the Hawaiian Islands) to a minimum known depth of 600 m (Pettibone 1991).

Macellicephala sp. SIO_BIC_A8368

Fig. 5B

Material examined. AD4913: A8368 (PQ449306).

Localities. Jacó Scar (~ 1817–1896 m).

Macellicephala sp. SIO_BIC_A9775

Fig. 5C

Material examined. AD4975: A9775 (PQ449325).

Localities. Mound 12 (1000 m).

Remarks. An undescribed species. At least six individuals were associated with the ambulacral groove of an asteroid, Thrissacanthias penicillatus (E7246).

Macellicephala sp. SIO_BIC_A10055

Fig. 5D, E

Material examined. S0213: A10055 (OP648305).

Localities. Jacó Summit (~ 730–820 m).

Macellicephala sp. SIO_BIC_A10094

Fig. 5F, G

Material examined. S0219: A10094 (PQ449266).

Localities. Rio Bongo Scar (659 m).

Remarks. Afflicted with copepod parasites.

Macellicephala sp. SIO_BIC_A10099

Figs 5H, 6A

Figure 6. 

Annelida: Polynoidae, representative live images A Macellicephala sp. SIO_BIC_A10099 (A10099) B Macellicephalinae sp. SIO_BIC_A8365 (A8365, dorsal view) C Macellicephalinae sp. SIO_BIC_A8365 (A8365, ventral view) D Macellicephalinae sp. SIO_BIC_A8458 (A8458) E Macellicephalinae sp. SIO_BIC_A10186 (A10186, dorsal view) F Macellicephalinae sp. SIO_BIC_A10186 (A10186, ventral view) G Peinaleopolynoe elvisi (A10059) H Peinaleopolynoe mineoi (MZUCR 1001-01). Scale bars: 1 cm (A, G); 1 mm (B–F, H).

Material examined. S0220: A10099 (OP648306; 16S: PQ304650).

Localities. Subduction Plume (3601 m).

Remarks. An undescribed species associated with a cladorhizid sponge, P1754.

Macellicephalinae sp. SIO_BIC_A8365

Fig. 6B, C

Material examined. AD4914: A8365 (PQ449304).

Localities. Jacó Scar (1839 m).

Remarks. Associated with a holothuroid, Achlyonice stet. (E7042 or E7043).

Macellicephalinae sp. SIO_BIC_A8458

Fig. 6D

Material examined. AD4923: A8458 (PQ449315).

Localities. Parrita Seep (~ 1037–1108 m).

Macellicephalinae sp. SIO_BIC_A10186

Fig. 6E, F

Material examined. S0230: A10186.

Localities. Mound Jaguar (1909 m).

Peinaleopolynoe elvisi Hatch, Liew, Hourdez & Rouse, 2020

Fig. 6G

Reference. Hatch et al. 2020**.

Additional material examined. S0214: A10059 (PQ449258).

Localities. Jacó Scar (1845–1887 m).

Distribution. Also known from a whale fall in Monterey Submarine Canyon, off California, 1820 m (type locality) and from cow bones experimentally deployed at 2091 m at Seamount 1, which lies on the CRM ca 41 km southwest of Jacó Scar (Hatch et al. 2020).

Remarks. A10059 was associated with a naturally occurring wood fall. All known occurrences of P. elvisi have been associated with vertebrate bones or wood (naturally occurring and experimentally deployed, for both substrates) (Hatch et al. 2020).

Peinaleopolynoe mineoi Hatch, Liew, Hourdez & Rouse, 2020

Fig. 6H

Reference. Hatch et al. 2020**.

Localities. Mound 12 (992–1011 m; type locality), Mound 11 (1010 m).

Distribution. Known only from the CRM seeps.

Remarks. All known occurrences of P. mineoi have been associated with wood (naturally occurring and experimentally deployed) or experimentally deployed vertebrate bones (Hatch et al. 2020).

Polynoidae sp. SIO_BIC_A8426

Fig. 7A–C

Figure 7. 

Annelida: Polynoidae, representative live images A Polynoidae sp. SIO_BIC_A8426 (A8426, on host holothuroid E7063) B Polynoidae sp. SIO_BIC_A8426 (A8426, dorsal view) C Polynoidae sp. SIO_BIC_A8426 (A8426, ventral view) D Polynoidae sp. SIO_BIC_A9652 (A9652, dorsal view) E Polynoidae sp. SIO_BIC_A9652 (A9652, ventral view) F Polynoidae sp. SIO_BIC_A9714 (A9714, dorsal view) G Polynoidae sp. SIO_BIC_A9714 (A9714, ventral view) H Polynoidae sp. SIO_BIC_A10082 (A10082, dorsal view). Scale bars: 1 cm (A, D–G); 1 mm (B, C, H).

Material examined. AD4922: A8426 (PQ449308).

Localities. Mound 12 (1006 m).

Remarks. Associated with a holothuroid, Bathyplotes sp. SIO_BIC_E7063.

Polynoidae sp. SIO_BIC_A9652

Fig. 7D, E

Material examined. AD4972: A9720; AD4973: A9652 (PQ449319), A9653.

Localities. Jacó Scar (1784 m).

Polynoidae sp. SIO_BIC_A9714

Fig. 7F, G

Material examined. AD4974: A9714 (PQ449321).

Localities. Mound 12 (~ 1001–1003 m).

Polynoidae sp. SIO_BIC_A10082

Figs 7H, 8A

Figure 8. 

Annelida: Polynoidae, Syllidae, and Nephtyidae, representative live images A Polynoidae sp. SIO_BIC_A10082 (A10082, ventral view) B Polynoidae sp. SIO_BIC_A10096 (A10096, dorsal view) C Polynoidae sp. SIO_BIC_A10096 (A10096, ventral view) D Polynoidae sp. SIO_BIC_A10189 (A10189, dorsal view) E Polynoidae sp. SIO_BIC_A10189 (A10189, ventral view) F Anguillosyllis sp. SIO_BIC_A12403 (A12403) G Synmerosyllis stet. (A1928) H Nephtys stet. (A1437, dorsal view). Scale bars: 1 mm (A, D–H); 1 cm (B, C).

Material examined. AD4919: A8421; AD4986: A9899; S0216: A10082 (PQ449262).

Localities. Quepos Slide (~ 308–410 m)

Remarks. A10082 was associated with bones from a naturally occurring sailfish carcass.

Polynoidae sp. SIO_BIC_A10096

Fig. 8B, C

Material examined. S0219: A10095, A10096 (PQ449267), A10098, A10109, A10110.

Localities. Rio Bongo Scar (~ 480–650 m).

Remarks. A10096 and A10098 were commensals in a sponge, Farrea occa (P1753).

Polynoidae sp. SIO_BIC_A10189

Fig. 8D, E

Material examined. AD4913: A8369; S0230: A10189 (PQ449271).

Localities. Jacó Scar (~ 1817–1896 m), Mound Jaguar (2000 m).

Remarks. A10189 was associated with a naturally occurring wood fall.

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Aphroditiformia | Syllidae

Anguillosyllis sp. SIO_BIC_A9613

Material examined. AD4975: A9613; AD4978: A9771.

Localities. Mound 12 (~ 992–999 m).

Remarks. An undescribed species. A9613 was associated with experimentally deployed wood and bone at 992 m.

Anguillosyllis sp. SIO_BIC_A12403

Fig. 8F

Reference. (Aguado et al. 2012), in which the published DNA sequences (JF903571, JF903680, JF903756) correspond to specimen A12403 from AT15-59, MC1.

Localities. Near Mound 12 (995 m).

Remarks. An undescribed species, morphologically similar to Anguillosyllis sp. SIO_BIC_A9613. This specimen was collected in a sediment core adjacent to Mound 12, ca 400 m from known sites of active seepage and likely representing the far-transition zone to the surrounding environment.

Synmerosyllis stet.

Fig. 8G

Reference. Aguado et al. (2012), in which the published DNA sequences (JF903573, JF903681, JF903759) correspond to specimen A1928 from AD4588.

Localities. Mound 12 (997 m).

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Nephtyiformia | Nephtyidae

Nephtys stet.

Figs 8H, 9A

Figure 9. 

Annelida: Nephtyidae, Pilargidae, and Chrysopetalidae, representative live images A Nephtys stet. (A1437, ventral view) B Sigambra sp. SIO_BIC_A9597 (A9597) C Chrysopetalinae sp. SIO_BIC_A8064 D Laubierus alvini (A1323) E Micospina auribohnorum (A1427) F Natsushima sashai (A1447) G Shinkai fontefridae (A1384) H Shinkai longipedata (A1360). Scale bars: 1 mm (A–F, H); 1 cm (G).

Material examined. AD4510: A1437.

Localities. Jacó Summit (742 m).

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Nephtyiformia | Pilargidae

Sigambra sp. SIO_BIC_A9597

Fig. 9B

Material examined. AD4503: A1346; AD4972: A9597; AD4987: A9843.

Localities. Mound 12 (~ 967–999 m), Jacó Scar (1795 m).

Remarks. An undescribed species.

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Hesionoidea | Chrysopetalidae

Chrysopetalinae sp. SIO_BIC_A8064

Fig. 9C

Material examined. AD4508: A1404, A2410; AD4914: A8063; AD4917: A8065; AD4922: A8064, A10280; AD4974: A9609, A9758; AD4985: A9853; AD4990: A9879.

Localities. Mound 12 (~ 965–1002 m), Parrita Seep (1401–1402 m), Jacó Scar (~ 1632–1886 m).

Remarks. An undescribed genus and species.

Laubierus alvini Aguado & Rouse, 2011

Fig. 9D

Reference. Aguado and Rouse 2011**.

Additional material examined. S0214: A10057 (PQ449257).

Localities. Mound 12 (~ 982–999 m), Mound 11 (~ 1004–1011 m; type locality), Jacó Scar (~ 1752–1860 m).

Distribution. Known only from the CRM seeps.

Remarks. As noted in the original description, L. alvini is a symbiont of the mussel Bathymodiolus earlougheri, but not of the two sympatric species subsequently described as B. billschneideri and B. nancyschneiderae. The worms are found among the gill filaments, with typically 2–25 individuals per host, and the number of individuals linearly correlates with the length of the host (Aguado and Rouse 2011).

Micospina auribohnorum Watson, Carvajal, Sergeeva, Pleijel & Rouse, 2016

Fig. 9E

Reference. Watson et al. 2016**.

Additional material examined. S0217: A10088 (PQ449265).

Localities. Jacó Summit (~ 750 m), Mound 12 (~ 1000 m), Mound 11 (~ 1040 m), The Thumb (1072 m; this study), Jacó Scar (~ 1800 m).

Distribution. Also known from a whale fall at 845 m off San Diego, California (type locality) (Watson et al. 2016).

Natsushima sashai Aguado & Rouse, 2011

Fig. 9F

Reference. Aguado and Rouse 2011**.

Localities. Mound 12 (~ 1000 m; type locality).

Distribution. Known only from the CRM seeps.

Remarks. A symbiont of the solemyid clam Acharax cf. johnsoni; the worms are found among the gill lamellae, with no more than four individuals per host, in three possible combinations: one female, one male and one female, or two males and two females (Aguado and Rouse 2011).

Shinkai fontefridae Aguado & Rouse, 2011

Fig. 9G

Reference. Aguado and Rouse 2011**.

Localities. Parrita Seep (1186 m), Parrita Scar (~ 1660 m), Jacó Scar (~ 1752–1800 m; type locality).

Distribution. Known only from the CRM seeps.

Remarks. Symbiont of the vesicomyid clams Phreagena soyoae and Archivesica gigas (previously cited as Calyptogena kilmeri and Vesicomya gigas, respectively); the worms are found between the gill lamellae and foot, typically with one male and one female per host (Aguado and Rouse 2011).

Shinkai longipedata Miura & Ohta, 1991

Fig. 9H

Reference. Aguado and Rouse 2011.

Localities. Mound 11 (~ 1019–1025 m).

Distribution. Originally described from hydrothermal vents at Iheya Ridge off southern Japan (Miura and Ohta 1991). The occurrences of S. longipedata at the CRM established the first record of this species in the eastern Pacific, based on morphological similarity to specimens from Japan and in the absence of DNA sequences from the type locality (Aguado and Rouse 2011). Genetic data from the type locality will be necessary to confirm the apparent trans-Pacific distribution of this species at both vents and seeps.

Remarks. Originally described as a commensal symbiont in the mantle cavity of the vesicomyid clam Calyptogena sp. (Miura and Ohta 1991). At the CRM seeps, the host is the vesicomyid clam Phreagena soyoae (previously identified as an “undescribed” vesicomyid); the worms are found between the gill lamellae and foot, typically with one male and one female per host (Aguado and Rouse 2011).

Vigtorniella sp. SIO_BIC_A8061

Fig. 10A

Figure 10. 

Annelida: Chrysopetalidae and Hesionidae, representative live images A Vigtorniella sp. SIO_BIC_A8061 (A8061) B Amphiduropsis cf. axialensis (A8110) C Gyptis robertscrippsi (A1750) D Gyptis sp. SIO_BIC_A10083 (A10083) E Leocrates gen. inc. (A10184) F Neogyptis jeffruoccoi (A1448) G Sirsoe dalailamai (MZUCR 401-01) H Sirsoe munki (A1409). Scale bars: 1 mm.

Material examined. AD4914: A8061, A8062.

Localities. Jacó Scar (~ 1632–1886 m).

Remarks. An undescribed species.

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Hesionoidea | Hesionidae

Amphiduropsis cf. axialensis (Blake & Hilbig, 1990)

Fig. 10B

Reference. Rouse et al. 2018.

Localities. Mound 12 (~ 984–997 m).

Remarks. The type locality of Amphiduropsis axialensis is hydrothermal vents at 1545 m on the Axial Seamount of the Juan de Fuca Ridge (Blake and Hilbig 1990). As discussed in Rouse et al. (2018), the specimens above (and other seep specimens from Hydrate Ridge off Oregon, 587–809 m, and the Guaymas Basin, Gulf of California, 1560–1613 m) are morphologically consistent with A. axialensis but are conservatively designated as A. cf. axialensis because DNA sequences are not available from the type locality.

Gyptis robertscrippsi Rouse, Carvajal & Pleijel, 2018

Fig. 10C

Reference. Rouse et al. 2018**.

Localities. Mound 12 (~ 982–1002 m; type locality), Mound 11 (~ 1019–1025 m), Jacó Scar (1783–1794 m).

Distribution. Known only from the CRM seeps.

Gyptis sp. SIO_BIC_A10083

Fig. 10D

Material examined. AD4919: A8114; S0216: A10083.

Localities. Quepos Slide (~ 379–398 m).

Remarks. An undescribed species.

Leocrates gen. inc.

Fig. 10E

Material examined. AD4914: A8113; S0230: A10184.

Localities. Jacó Scar (1886 m), Mound Jaguar (1909 m).

Remarks. Taxonomic placement of these specimens requires further assessment, particularly in light of recent revisions to several hesionid genera (Salazar-Vallejo 2020b).

Neogyptis jeffruoccoi Rouse, Carvajal & Pleijel, 2018

Fig. 10F

Reference. Rouse et al. 2018**.

Localities. Mound 12 (~ 988–997 m; type locality), Mound 11 (~ 1019–1025 m).

Distribution. Also known from seeps in the Guaymas Basin, Gulf of California, 1572–1613 m, and off Del Mar, California, 1020 m (Rouse et al. 2018).

Remarks. Found in the mantle cavity of the solemyid clam Acharax cf. johnsoni, with either one individual or two (one male and one female) per host (Rouse et al. 2018).

Sirsoe dalailamai Rouse, Carvajal & Pleijel, 2018

Fig. 10G

Reference. Rouse et al. 2018**.

Localities. Mound 12 (997 m), Parrita Seep (1402 m), Jacó Scar (1784–1795 m; type locality).

Distribution. Also described from a seep in the Guaymas Basin, Gulf of California, 1560–1613 m (Rouse et al. 2018).

Remarks. Associated with vestimentiferan and mussel communities at areas of active methane seepage (Rouse et al. 2018).

Sirsoe munki Rouse, Carvajal & Pleijel, 2018

Fig. 10H

Reference. Rouse et al. 2018**.

Additional material examined. S0217: A10087 (PQ449264).

Localities. Jacó Slope (1063 m), The Thumb (1072 m; this study), Jacó Scar (~ 1800 m; type locality).

Distribution. Known only from the CRM seeps.

Sirsoe sp. SIO_BIC_A8288

Fig. 11A

Figure 11. 

Annelida: Hesionidae, Nereididae, Sphaerodoridae, and Lacydoniidae, representative images. Live specimens are depicted unless otherwise specified A Sirsoe sp. SIO_BIC_A8288 (A8288, preserved specimen) B Vrijenhoekia sp. A sec. Summers et al. 2015 (A9606) C Nereis stet. (A8291) D Nereididae sp. SIO_BIC_A9614 (A9614) E Pectinereis strickrotti (A9889) F Sphaerephesia sp. SIO_BIC_A10069 (A10069) G Sphaerodoropsis sp. SIO_BIC_A10068 (A10068) H Lacydonia sp. SIO_BIC_A1432 (A1432). Scale bars: 1 mm (A–D, F–H); 1 cm (E).

Material examined. AD4909: A8288 (PQ449293).

Localities. Mound 12 (990 m).

Remarks. An undescribed species associated with a microbial mat.

Vrijenhoekia sp. A sec. Summers et al. 2015

Fig. 11B

Material examined. AD4508: A1406; AD4907: A8101; AD4974: A9606, A9608, A9612, A9615; AD4988: A9926.

Localities. Mound 11 (1010 m), Mound 12 (~ 990–999 m), Parrita Seep (1419 m).

Remarks. The undescribed species Vrijenhoekia sp. A was previously known only from a single specimen, SIO-BIC A3255, from a seep in the Guaymas Basin, Gulf of California, 1565–1598 m; the specimen was collected in poor condition and diagnostic morphological features could not be assessed (Summers et al. 2015). The CRM specimens represent the first records of this morphospecies beyond the Guaymas Basin and expand the known depth range to ~ 1000–1600 m. The CRM specimens were associated with naturally occurring and experimentally deployed wood (A1406, A9606, A9608, A9926) or experimentally deployed bone (A9615).

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Nereididae

These specimens will be further examined and compared to other eastern Pacific Nereididae in a separate work.

Nereis stet.

Fig. 11C

Material examined. AD4906: A8258; AD4910: A8291.

Localities. Mound 12 (997–1002 m).

Remarks. A8258 was associated with experimentally deployed bone.

Nereididae sp. SIO_BIC_A9614

Fig. 11D

Material examined. AD4974: A9614.

Localities. Mound 12 (992 m)

Remarks. An undescribed species. Associated with experimentally deployed wood and pig bones.

Pectinereis strickrotti Villalobos-Guerrero, Huč, Tilic, Hiley & Rouse, 2024

Fig. 11E

Reference. Villalobos-Guerrero et al. 2024**.

Material examined. AD4984: A9889.

Localities. Mound 12 (996–1010 m).

Distribution. Known only from the CRM seeps.

Remarks. Known from epitokous males, all collected while swimming just above the seafloor, and from a fragment of an atokous infaunal female recovered from a push core sample (Villalobos-Guerrero et al. 2024).

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Glyceriformia | Sphaerodoridae

Sphaerephesia sp. SIO_BIC_A10069

Fig. 11F

Material examined. S0214: A10069 (PQ449261; no voucher remaining).

Localities. Jacó Scar (1875 m).

Remarks. Associated with a naturally occurring wood fall. The closest COI BLASTN result on GenBank was a specimen of Sphaerephesia cf. discolis (Borowski, 1994) from the Brazilian Basin, 5180 m (KR019875.1, 95.39% identity, formerly Sphaerodoropsis cf. discolis) (Capa et al. 2016, 2019). Sphaerephesia discolis was originally described from the Peru Basin, 4152 m (Capa et al. 2019), so a comparison of the CRM specimen to material from the type locality would be informative.

Sphaerodoropsis sp. SIO_BIC_A10068

Fig. 11G

Material examined. S0214: A10068 (PQ449260).

Localities. Jacó Scar (1875 m).

Remarks. Associated with a naturally occurring wood fall.

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Phyllodociformia

These specimens will be further examined and compared to other eastern Pacific Lacydonia in a separate work.

Lacydonia sp. SIO_BIC_A1432

Fig. 11H

Material examined. AD4504: A1525, A1526; AD4510: A1432.

Localities. Jacó Summit (~ 741–744 m), Mound 11 (~ 1004–1011 m).

Remarks. An undescribed species.

Lacydonia sp. SIO_BIC_A1606

Material examined. AD4510: A1606.

Localities. Jacó Summit (~ 741–744 m).

Remarks. An undescribed species.

Lacydonia sp. SIO_BIC_A9774

Fig. 12A

Figure 12. 

Annelida: Lacydoniidae and Phyllodocidae, representative live images A Lacydonia sp. SIO_BIC_A9774 (A9774) B Eulalia sp. SIO_BIC_A1383 (A1383, wide view) C Eulalia sp. SIO_BIC_A1383 (A1383, anterior detail) D Galapagomystides patricki (A9934) E Galapagomystides verenae (A10044) F Phyllodoce sp. SIO_BIC_A1469 (A1469) G Phyllodoce sp. SIO_BIC_A8454 (A8454, wide view) H Phyllodoce sp. SIO_BIC_A8454 (A8454, anterior detail). Scale bars: 1 mm.

Material examined. AD4588: A1925; AD4978: A9774; AD4990: A9880; S0217: A10090 (MZ562520).

Localities. The Thumb (~ 940–1070 m), Mound 12 (~ 996–999 m), Parrita Seep (1401 m).

Remarks. An undescribed species.

Lacydonia sp. SIO_BIC_A16347

Material examined. AD4504: A16347.

Localities. Mound 11 (~ 1004–1011 m).

Remarks. An undescribed species.

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Phyllodociformia | Phyllodocidae

Eulalia sp. SIO_BIC_A1383

Fig. 12B, C

Material examined. AD4506: A1383 (PQ449278).

Localities. Parrita Seep (~ 1030–1179 m).

Galapagomystides patricki Pearson & Rouse, 2022

Fig. 12D

Reference. Pearson and Rouse 2022**.

Localities. Parrita Seep (~ 1401–1419 m; type locality), Jacó Scar (1762–1785 m).

Distribution. Known only from the CRM seeps and vicinity. One paratype was collected from a multicore sample ca 21 km northwest of Parrita Seep, at 805 m depth (Cruise AT15-44, Multicore 17: 9.1713, -84.7459) (Pearson and Rouse 2022).

Remarks. Some specimens were associated with empty vestimentiferan tubes (Pearson and Rouse 2022).

Galapagomystides verenae (Blake & Hilbig, 1990)

Fig. 12E

Reference. Pearson and Rouse 2022.

Localities. Mound 12 (~ 984–997 m), Parrita Seep (~ 1400–1410 m), Jacó Scar (~ 1632–1908 m).

Distribution. Originally described from vents on the Juan de Fuca and Explorer Ridges, 1545–2195 m (Blake and Hilbig 1990). Also known from seeps in the Guaymas Basin, Gulf of California, to the CRM, 1572 to ~ 1800 m (Pearson and Rouse 2022).

Remarks. At the CRM seeps, G. verenae is associated with the tubes of juvenile Escarpia spicata and may feed on the blood of vestimentiferans (Pearson and Rouse 2022).

Phyllodoce sp. SIO_BIC_A1469

Fig. 12F

Material examined. AT15-44 MC1-2: A1469 (PQ449283).

Localities. Near Mound 12 (1019 m).

Remarks. This specimen was collected in a sediment core adjacent to Mound 12, ca 500 m from known sites of active seepage and likely representing the far-transition zone to the surrounding environment.

Phyllodoce sp. SIO_BIC_A8454

Fig. 12G, H

Material examined. AD4505: A1366; AD4508: A1399; AD4922: A8454 (PQ449312); AD4975: A9795; AD4978: A9798 (PQ449326).

Localities. Mound 12 (~ 964–1009 m), Mound 11 (~ 1019–1025 m), Parrita Seep (~ 1401–1419 m).

Phyllodocidae sp. SIO_BIC_A10054

Fig. 13A

Figure 13. 

Annelida: Phyllodocidae, Paralacydonia, Eunicidae, and Onuphidae, representative live images A Phyllodocidae sp. SIO_BIC_A10054 (A10054) B Sige sp. SIO_BIC_A8263 (A8263) C Sige sp. SIO_BIC_A8263 (A8356) D Sige sp. SIO_BIC_A8430 (A8430) E Paralacydonia stet. (A1412, wide view) F Lumbrineridae stet. (A1370) G Eunicidae stet. (A1431) H Hyalinoecia stet. (A10060). Scale bars: 1 mm (A–G); 1 cm (H)

Material examined. S0212: A10054 (PQ449256).

Localities. Jacó Scar (~ 1780–1860 m).

Sige sp. SIO_BIC_A8263

Fig. 13B, C

Material examined. AD4906: A8263 (PQ449290); AD4912: A8356 (PQ449301).

Localities. Mound 12 (1002 m), Jacó Scar (~ 1795–1859 m).

Sige sp. SIO_BIC_A8430

Fig. 13D

Material examined. AD4907: A8284 (PQ449292); AD4922: A8430 (PQ449311).

Localities. Mound 12 (~ 990–1002 m).

Remarks. A8430 was associated with a naturally occurring wood fall.

Annelida | Polychaeta | Errantia | Aciculata | Phyllodocida | Phyllodociformia

Paralacydonia stet.

Fig. 13E

Material examined. AD4509: A1412.

Localities. Jacó Scar (1855 m).

Annelida | Polychaeta | Errantia | Aciculata | Eunicida | Oenonoidea

Lumbrineridae stet.

Fig. 13F

Material examined. AD4505: A1370 (PQ448999).

Localities. Mound 11 (~ 1019–1025 m).

Annelida | Polychaeta | Errantia | Aciculata | Eunicida | Eunicoidea | Eunicidae

Eunicidae stet.

Fig. 13G

Material examined. AD4510: A1431; AD4914: A8386; AD4985: A9895 (PQ449332).

Localities. Mound 12 (991 m), Jacó Summit (741 m), Jacó Scar (1798 m).

Remarks. The closest COI BLASTN result on GenBank was Leodice antarctica (Baird, 1869) (GQ497532.1, 92.64% identity, formerly Eunice antarctica), known from Antarctic and sub-Antarctic waters (Baird 1869). The identification of species of Eunice and Leodice, among other genera, is complicated by the need for taxonomic revision (Zanol et al. 2021).

Annelida | Polychaeta | Errantia | Aciculata | Eunicida | Eunicoidea | Onuphidae

Hyalinoecia stet.

Fig. 13H

Material examined. AD4510: A1440; S0214: A10060 (PQ449259).

Localities. Jacó Summit (~ 741–744 m), Jacó Scar (1875 m).

Annelida | Polychaeta | Errantia | Aciculata | Eunicida | Dorvilleidae

Ophryotrocha cf. batillus Wiklund et al., 2012

Fig. 14A

Figure 14. 

Annelida: Dorvilleidae: Ophryotrocha, representative live images A Ophryotrocha cf. batillus (A9610) B Ophryotrocha cf. flabella (A1410) C Ophryotrocha cf. platykephale (A9878) D Ophryotrocha sp. SIO_BIC_A8367 (A8367) E Ophryotrocha sp. SIO_BIC_A9611 (A9611) F Ophryotrocha sp. SIO_BIC_A9723 (A9723) G Ophryotrocha sp. SIO_BIC_A9800 (A9800) H Ophryotrocha sp. SIO_BIC_A10052 (A10052). Scale bars: 1 mm.

Material examined. AD4974: A9610 (MT444001).

Localities. Mound 12 (992 m).

Remarks. Associated with experimentally deployed wood. To be discussed in a forthcoming study. Ophryotrocha batillus was originally described from whale falls and wood falls off southern California, 960–1960 m (Wiklund et al. 2012).

Ophryotrocha cf. flabella Wiklund et al., 2012

Fig. 14B

Material examined. AD4509: A1410 (MT435616); AD4988: A9928 (MT435618; no specimen remaining), A9929 (MT435617).

Localities. Mound 11 (1010 m), Jacó Slope (1064 m).

Remarks. To be discussed in a forthcoming study. Ophryotrocha flabella was originally described from whale falls off southern California, 960–1960 m (Wiklund et al. 2012). Specimens A9928 and A9929 were associated with a naturally occurring wood fall.

Ophryotrocha cf. platykephale Blake, 1985

Fig. 14C

Material examined. AD4990: A9878 (MT435620).

Localities. Parrita Seep (~ 1400–1435 m).

Remarks. To be discussed in a forthcoming study. Ophryotrocha platykephale was originally described from sedimented vents at 2000–2030 m in the Guaymas Basin, Gulf of California (Blake 1985; Solís-Weiss and Hilbig 1992).

Ophryotrocha sp. SIO_BIC_A8367

Fig. 14D

Material examined. AD4914: A8367 (PQ449305).

Localities. Jacó Scar (~ 1632–1886 m).

Remarks. Likely an undescribed species.

Ophryotrocha sp. SIO_BIC_A9611

Fig. 14E

Material examined. AD4974: A9611 (PQ449317).

Localities. Mound 12 (992 m).

Remarks. An undescribed species, associated with experimentally deployed bone and wood.

Ophryotrocha sp. SIO_BIC_A9723

Fig. 14F

Material examined. AD4976: A9723 (PQ449322).

Localities. Jacó Scar (1887 m).

Remarks. Likely an undescribed species. Associated with experimentally deployed wood.

Ophryotrocha sp. SIO_BIC_A9800

Fig. 14G

Material examined. AD4912: A8354; AD4913: A8360; AD4978: A9800 (MT435612).

Localities. Mound 12 (999 m), Jacó Scar (~ 1795–1859 m).

Remarks. An undescribed species.

Ophryotrocha sp. SIO_BIC_A10052

Fig. 14H

Material examined. S0213: A10052 (MT435579).

Localities. Jacó Summit (~ 730–820 m).

Remarks. An undescribed species.

Ophryotrocha sp. SIO_BIC_A10084

Fig. 15A

Figure 15. 

Annelida: Dorvilleidae and Myzostomida, representative live images A Ophryotrocha sp. SIO_BIC_A10084 (A10084) B Ophryotrocha sp. SIO_BIC_A10106 (A10106) C Ophryotrocha sp. SIO_BIC_ A10114 (A10114) D Parougia ceruleibohnorum (A1446) E Parougia cf. billiemiroae (A9678) F Parougia cf. sulleyi (A1333) G Parougia theloniousblueski (A1337) H Eenymeenymyzostoma sp. SIO_BIC_A8428 (A8428, dorsal view). Scale bars: 1 mm.

Material examined. S0217: A10084 (MT435566), MZUCR 1512-01; S0219: A10113 (MT435562).

Localities. Rio Bongo Scar (610 m), The Thumb (1072 m).

Remarks. An undescribed species.

Ophryotrocha sp. SIO_BIC_A10106

Fig. 15B

Material examined. S0219: A10106 (PQ449268).

Localities. Rio Bongo Scar (661 m).

Remarks. An undescribed species associated with a naturally occurring wood fall.

Ophryotrocha sp. SIO_BIC_ A10114

Fig. 15C

Material examined. S0219: A10114 (MT435596), MZUCR 1511-01.

Localities. Rio Bongo Scar (~ 480–650 m).

Remarks. An undescribed species to be described in a forthcoming study.

Parougia ceruleibohnorum Yen & Rouse, 2020

Fig. 15D

Reference. Yen and Rouse 2020**.

Localities. Mound 12 (996 m), Parrita Seep (~ 1401–1419 m; type locality).

Distribution. Known only from the CRM seeps.

Parougia cf. billiemiroae Yen & Rouse, 2020

Fig. 15E

Reference. Yen and Rouse 2020.

Localities. Jacó Scar (1796 m).

Remarks. Parougia billiemiroae sensu stricto is found at seeps, 587–1583 m, from Hydrate Ridge off Oregon (type locality) to the Guaymas Basin, Gulf of California (Yen and Rouse 2020). As discussed in Yen and Rouse (2020), the CRM single specimen A9678 is morphologically indistinguishable from P. billiemiroae sensu stricto, but its COI haplotype is up to 5.8% divergent from the type series and has been conservatively designated P. cf. billiemiroae.

Parougia cf. sulleyi Yen & Rouse, 2020

Fig. 15F

Reference. Yen and Rouse 2020.

Localities. Mound 12 (~ 987–997 m).

Remarks. P. sulleyi sensu stricto is found at seeps, 600–1600 m, from Hydrate Ridge off Oregon to the Guaymas Basin, Gulf of California (type locality) (Yen and Rouse 2020). As discussed in Yen and Rouse (2020), the CRM specimens are morphologically indistinguishable from P. sulleyi sensu stricto but share a COI haplotype that is 7.4% divergent from the type series. Parougia cf. sulleyi is the same taxon as the “Dorvillea sp.” documented by Thurber et al. (2012) as a consumer of archaea at the CRM seeps, representing one of the first records of “archivory” by a metazoan (Yen and Rouse 2020).

Parougia theloniousblueski Yen & Rouse, 2020

Fig. 15G

Reference. Yen and Rouse 2020**.

Localities. Mound 12 (987–997 m), Mound 11 (1010 m; type locality).

Distribution. Known only from the CRM seeps.

Annelida | Polychaeta | Errantia | Aciculata incertae sedis | Myzostomida

Eenymeenymyzostoma sp. SIO_BIC_A8428

Figs 15H, 16A

Figure 16. 

Annelida: Myzostomida, Nerillidae, and Sabellidae, representative live images A Eenymeenymyzostoma sp. SIO_BIC_A8428 (A8428, ventral view) B Myzostoma josefinae (A8362) C Pulvinomyzostomum inaki (A1579, dorsal and ventral views of female with dwarf males) D Pulvinomyzostomum sp. SIO_BIC_A8361 (A8361, dorsal and ventral views of female) E Pulvinomyzostomum sp. SIO_BIC_A8361 (A8361, dorsal and ventral views of male) F Nerillidae stet. (A9797) G Bispira sp. SIO_BIC_A9587 (A1396) H Bispira sp. SIO_BIC_A9587 (A1460, in tubes attached to rocks photographed ex situ in the shipboard laboratory). Scale bars: 1 mm.

Material examined. AD4501: A1476; AD4503: A1340; AD4922: A8427 (PQ449309), A8428, A8431.

Localities. Mound 12 (~ 966–995 m).

Remarks. An undescribed species associated with the antipatharian coral Lillipathes ritamariae.

Myzostoma josefinae Summers & Rouse in Summers et al. 2014

Fig. 16B

Material examined. AD4913: A8362.

Localities. Jacó Scar (1878 m).

Distribution. Originally described from a whale fall at 1020 m in Monterey Submarine Canyon, off California (type locality) and in the vicinity of sedimented vents and seeps at ~ 1350 m in the Guaymas Basin, Gulf of California (Summers et al. 2014b).

New records. The CRM specimen represents a new southern record and a new maximum depth record for this species.

Remarks. The specimen, showing the distinctive paired elongate caudal appendages, was associated with the crinoid Psathyrometra cf. fragilis (E7034), consistent with previous records of M. josefinae on P. fragilis (Summers et al. 2014b).

Pulvinomyzostomum inaki Summers & Rouse in Summers et al. 2014

Fig. 16C

Reference. Summers et al. 2014b**.

Localities. Jacó Scar (1789 m; type locality).

Distribution. Known only from the CRM seeps.

Remarks. Associated with an antedonid crinoid (E4399) (Summers et al. 2014b).

Pulvinomyzostomum sp. SIO_BIC_A8361

Fig. 16D, E

Material examined. AD4913: A8361 (PQ449303).

Localities. Jacó Scar (1878 m)

Remarks. An undescribed species. One female and one male were associated with the crinoid Psathyrometra cf. fragilis (E7034).

Annelida | Polychaeta | Errantia | Aciculata incertae sedis | Nerillidae

Nerillidae stet.

Fig. 16F

Material examined. AD4979: A9797.

Localities. Quepos Slide (~ 380–395 m).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Sabellida | Sabellidae

Bispira sp. SIO_BIC_A9587

Figs 16G, H, 17A

Figure 17. 

Annelida: Sabellidae and Serpulidae, representative live images A Bispira sp. SIO_BIC_A9587 (A9587) B Chone sp. SIO_BIC_A8422 (A8422) C Chone sp. SIO_BIC_A8462 (A8462) D Jasmineira stet. (A8282) E Pseudopotamilla sp. SIO_BIC_A1455 (A1455) F Pseudopotamilla sp. SIO_BIC_A9732 (A9732) G Sabellidae sp. SIO_BIC_ A8286 (A8286) H Hyalopomatus sp. SIO_BIC_A1434 (A1434). Scale bars: 1 cm (A); 1 mm (B–H).

Reference. Goffredi et al. (2020) for characterization of bacterial symbiosis; specimen A9587 was erroneously cited as A9598.

Material examined. AD4508: A1396; AD4513: A1460 (PQ449282; 18S: PQ304645); AD4916: A8387; AD4971: A9587.

Localities. Parrita Seep (1402 m; this study), Jacó Scar (~ 1604–1854 m).

Remarks. An undescribed species, abundant at zones of active seepage and utilizing methanotrophic bacterial symbionts for nutrition (Goffredi et al. 2020).

Chone sp. SIO_BIC_A8422

Fig. 17B

Material examined. AD4918: A8419; AD4919: A8422.

Localities. Quepos Slide (~ 379–410 m).

Remarks. Likely an undescribed species (María Ana Tovar-Hernández, pers. comm. 8 August 2020).

Chone sp. SIO_BIC_A8462

Fig. 17C

Material examined. AD4916: A8389; AD4919: A8462 (16S: PQ304651).

Localities. Parrita Seep (~ 1400–1410 m), Jacó Scar (1746 m).

Remarks. Likely an undescribed species (María Ana Tovar-Hernández, pers. comm. 8 August 2020).

Jasmineira stet.

Fig. 17D

Material examined. AD4907: A8282.

Localities. Mound 12 (999 m).

Pseudopotamilla sp. SIO_BIC_A1455

Fig. 17E

Material examined. AD4512: A1455; AD4918: A8418; AD4979: A9796.

Localities. Quepos Slide (~ 338–411 m).

Remarks. An undescribed species.

Pseudopotamilla sp. SIO_BIC_A9732

Fig. 17F

Material examined. AD4978: A9732.

Localities. Mound 12 (~ 996–999 m).

Sabellidae sp. SIO_BIC_A8286

Fig. 17G

Material examined. AD4908: A8286 (18S: PQ304646), A8287.

Localities. Mound 12 (1000 m).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Sabellida | Serpulidae

Hyalopomatus sp. SIO_BIC_A1434

Fig. 17H

Reference. Rouse and Kupriyanova (2021) for DNA sequences and phyloge­netic analysis.

Material examined. AD4510: A1434.

Localities. Jacó Summit (741–745 m).

Remarks. Possibly an undescribed species (Rouse and Kupriyanova 2021).

Laminatubus joycebrooksae Rouse & Kupriyanova, 2021

Fig. 18A

Figure 18. 

Annelida: Serpulidae, Spionidae, and Opheliidae, representative live images A Laminatubus joycebrooksae (A1315) B Laminatubus paulbrooksi (MZUCR 1506-01) C Spirorbinae stet. (A1385, body not visible) D Aonides sp. SIO_BIC_A1344 (A1344) E Lindaspio dibranchiata (A10053) F Prionospio stet. (A1415) G Opheliidae stet. (A9938) H Ophelina sp. 3 sec. Law et al. 2014 (A1898). Scale bars: 1 cm (A, B); 1 mm (C–H).

Reference. Rouse and Kupriyanova 2021**.

Localities. Mound 12 (~ 1000 m; type locality).

Distribution. Known only from the CRM seeps.

Laminatubus paulbrooksi Rouse & Kupriyanova, 2021

Fig. 18B

Reference. Rouse and Kupriyanova 2021**.

Localities. Parrita Seep (1402 m), Jacó Scar (~ 1800 m; type locality).

Distribution. Also known from seeps in the Guaymas Basin and Pescadero Basin, Gulf of California, 1565–2478 m (Rouse and Kupriyanova 2021).

Remarks. Abundant at zones of active seepage, this species utilizes methanotrophic bacterial symbionts for nutrition (Goffredi et al. 2020).

Protis stet.

Material examined. AD4506: A1553 (18S: PQ304668; no image available).

Localities. Parrita Seep (1186 m).

Remarks. We thank Elena Kupriyanova (Australian Museum Research Institute) for generating the 18S sequence.

Spirorbinae stet.

Fig. 18C

Material examined. AD4507: A1385.

Localities. Parrita Scar (~ 1659–1667 m).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Spionida | Spionidae

Aonides sp. SIO_BIC_A1344

Fig. 18D

Material examined. AD4503: A1344; AD4505: A1372, MZUCR 1509-01.

Localities. Mound 12 (~ 967–995 m), Mound 11 (~ 1019–1025 m).

Remarks. An undescribed species to be described in a forthcoming study.

Lindaspio dibranchiata Blake & Maciolek, 1992

Fig. 18E

Material examined. AD4511: A1453 (PQ449281); AD4972: A9601 (PQ449316); S0213: A10053 (PQ449255).

Localities. Jacó Summit (~ 730–820 m), Mound 12 (989 m), Jacó Scar (~ 1791–1800 m).

Distribution. Originally described from sedimented vents in the Guaymas Basin, Gulf of California, 2004–2008 m (Blake and Maciolek 1992).

New records: The CRM specimens represent new southern records, the first records from seeps, and, for specimen A10053, a new minimum depth for this species (820 m as the most conservative value). The COI sequences for the Costa Rica specimens were identical to that of a specimen from the type locality: A3258 (PQ432663) from 1581 m at Pinkie’s "Vent", Guaymas Basin.

Prionospio stet.

Fig. 18F

Material examined. AD4509: A1415; AD4979: A9809.

Localities. Quepos Slide (393 m), Jacó Scar (1855 m).

Remarks. These specimens are members of the Prionospio complex; the shape of the head of A1415 is consistent with Apoprionospio, but some sources place this genus into synonymy with Prionospio (Vasily Radashevsky, pers. comm. 8 July 2021).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Capitellida | Opheliidae

Opheliidae stet.

Fig. 18G

Material examined. AD4971: A9651; AD4972: A9596; AD4977: A9730; AD4989: A9938 (PQ449337).

Localities. Jacó Scar (1783–1796 m).

Remarks. A9651 likely represents an undescribed species of Ophelina (Sergio Salazar-Vallejo, pers. comm. 12 February 2020).

Ophelina sp. 3 sec. Law et al. 2014

Fig. 18H

Reference. Law et al. (2014), in which GenBank sequences published under the temporary code F14588 (KF511809, KF511823, KF511847, KF511864) correspond to specimen A1898 from AD4587.

Localities. Mound 12 (~ 990–996 m).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Capitellida | Capitelliformia | Thalassematidae

We refer to the clade formerly known as Echiura using the revised taxonomy of Goto et al. (2020).

Prometor stet.

Fig. 19A

Figure 19. 

Annelida: Thalassematidae, Capitellidae, Scalibregmatidae, Maldanidae, and Ampharetidae, representative live images A Prometor stet. (A9638) B Capitellidae stet. (A1418) C Scalibregma stet. (A1391) D Travisia stet. (A1386) E Nicomache cf. lokii (A8257) F Notoproctus sp. SIO_BIC_A9801 (A9801) G Notoproctus sp. SIO_BIC_A9802 (A9802) H Ampharetini stet. (A1377). Scale bars: 1 mm (A–C, E–H); 1 cm (D).

Material examined. AD4971: A9638 (PQ449318).

Localities. Jacó Scar (1824 m).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Capitellida | Capitelliformia | Capitellidae

Capitellidae stet.

Fig. 19B

Material examined. AD4506: A1376; AD4508: A1403; AD4509: A1418; AD4976: A9755 (16S: PQ304666).

Localities. Parrita Seep (~ 1186–1419 m), Jacó Scar (~ 974–1887 m).

Remarks. Associated with vesicomyid clams (A1376, A1418), Lamellibrachia barhami (A1403), or experimentally deployed wood (A9755).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Terebellida | Scalibregmatidae

Scalibregma stet.

Fig. 19C

Material examined. AD4507: A1391 (PQ449279); AD4914: A8385.

Localities. Parrita Scar (~ 1659–1667 m), Jacó Scar (1886 m).

Travisia stet.

Fig. 19D

Material examined. AD4507: A1386.

Localities. Parrita Scar (~ 1659–1663 m).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Terebellida | Maldanomorpha | Maldanidae

Nicomache cf. lokii Kongsrud & Rapp, 2012

Fig. 19E

Material examined. AD4504: A1350 (PQ450403); AD4509: A1420 (PQ450404); AD4906: A8257; AD4911: A8295.

Localities. Mound 11 (~ 1002–1011 m), Mound 12 (995–1001 m), Jacó Scar (~ 974–1856 m).

Remarks. The closest COI BLASTN results on GenBank were sequences of Nicomache lokii (95.03–98.17% identity to A1350, 95.18–98.31% identity to A1420), and the closest matches (MG975502.1, FR877578.1) were from the type locality of the Loki’s Castle vent system on the Arctic Mid-Ocean Ridge at 2350 m (Kongsrud and Rapp 2012; Eilertsen et al. 2018). Nicomache lokii shows genetic connectivity across vents and seeps in the Arctic, Barbados Trench, and East Scotia Sea, 1262–4930 m, with a maximum intraspecific pairwise distance of 4.1% (K2P) (Eilertsen et al. 2018), so further genetic and morphological comparisons to the CRM specimens are warranted.

Notoproctus sp. SIO_BIC_A9801

Fig. 19F

Material examined. AD4978: A9801 (PQ449327).

Localities. Mound 12 (997 m).

Remarks. This specimen showed a COI difference of 19.1% (uncorrected) from A9802 (below) so we regard them as separate species.

Notoproctus sp. SIO_BIC_A9802

Fig. 19G

Material examined. AD4978: A9802 (PQ449328).

Localities. Mound 12 (997 m).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Terebellida | Terebelliformia | Ampharetidae

Ampharetini stet.

Fig. 19H

Material examined. AD4506: A1377 (PQ450382).

Localities. Parrita Seep (1030 m).

Amphisamytha fauchaldi Solís-Weiss & Hernández-Alcántara, 1994

Fig. 20A

Figure 20. 

Annelida: Ampharetidae, Trichobranchidae, and Terebellidae, representative live images A Amphisamytha fauchaldi (A8352) B Grassleia cf. hydrothermalis (A12401) C Pavelius sp. EP-B sec. Stiller et al. 2020 (A1894) D Terebellides stet. (A1293) E Biremis sp. SIO_BIC_A10093 (A10093) F Polycirrus stet. (A10115) G Eupolymnia cf. heterobranchia (A8296) H Haplotype network of Eupolymnia cf. heterobranchia COI sequences. Scale bars: 1 mm (A–D, F, G); 1 cm (E).

References. Levin et al. 2012; Stiller et al. 2013.

Additional material examined. AD4906: A8260 (PQ449288, PQ449289); AD4912: A8352 (PQ449299, PQ449300); AD4913: A8358 (PQ449302); AD4914: A12602 (PQ449273).

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Distribution. Originally described from sedimented hydrothermal vents at 2000 m in the Guaymas Basin, Gulf of California (Solís-Weiss and Hernández-Alcántara 1994), A. fauchaldi is also found at seeps at Hydrate Ridge off Oregon, with an overall depth range of 600–2860 m (Stiller et al. 2013).

Grassleia cf. hydrothermalis Solís-Weiss, 1993

Fig. 20B

Material examined. AD4510: A12401 (PQ449272).

Localities. Jacó Summit (744 m).

Remarks. The closest COI BLASTN result on GenBank was a specimen identified as Grassleia cf. hydrothermalis from seeps at 1572–1583 m in the Guaymas Basin, Gulf of California (KX497032.1, 96.51% identity). Grassleia hydrothermalis was described from vents at the Escabana Trough, Gorda Ridge, off northern California, at 3271 m (Solís-Weiss 1993), and has been reported from seeps at 595 m off the Cascadia Margin (Reuscher et al. 2012). Genetic sampling from the type locality will be important to ascertain the distribution of this species.

Pavelius sp. EP-B sec. Stiller et al. 2020

Fig. 20C

Material examined. AD4586: A1887 (PQ449284); AD4587: A1894 (PQ449285).

Localities. Mound 12 (~ 982–998 m).

Remarks. The CRM specimens represent records of an undescribed species also reported from seeps at Hydrate Ridge off Oregon, 809 m, as cited in supplementary table S2 of Stiller et al. (2020).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Terebellida | Terebelliformia | Trichobranchidae

Terebellides stet.

Fig. 20D

Material examined. AT15-44 MC1-2: A1293.

Localities. Near Mound 12 (1019 m).

Remarks. This specimen was collected in the upper 1 cm of a sediment core adjacent to Mound 12, ca 500 m from known sites of active seepage and likely representing the far-transition zone to the surrounding environment.

Annelida | Polychaeta | Sedentaria | Canalipalpata | Terebellida | Terebelliformia | Terebellidae | Polycirrini

Biremis sp. SIO_BIC_A10093

Fig. 20E

Material examined. S0218: A10091, A10092, A10093.

Localities. Parrita Scar (1110–1470 m).

Remarks. An undescribed species.

Polycirrus stet.

Fig. 20F

Material examined. S0219: A10067, A10097, A10115 (PQ449270).

Localities. Rio Bongo Scar (609–659 m).

Remarks. These specimens were buried or partially buried in soft sediments with tentacles extended.

Annelida | Polychaeta | Sedentaria | Canalipalpata | Terebellida | Terebelliformia | Terebellidae | Procleini

Eupolymnia cf. heterobranchia (Johnson, 1901)

Fig. 20G

Material examined. AD4906: A8259 (PQ449287); AD4910: A8280 (PQ449291), A8296 (PQ449294), A8297 (PQ450386); AD4911: A8299 (PQ449295), A8301 (PQ449296).

Localities. Mound 12 (998–1002 m), Jacó Scar (1758 m).

Remarks. Likely an undescribed species, with morphological similarity to Eupolymnia heterobranchia, known from shallow waters from Alaska to Mexico (Banse 1980). The COI sequences showed low identity (~ 80–82%) to GenBank sequences of E. heterobranchia from the type locality of Puget Sound (Johnson 1901) (HQ932678.1, HM473379.1, HM473380.1, MN138388.1). Eupolymnia is paraphyletic, and nomenclatural revision requires further phylogenetic sampling (Stiller et al. 2020).

The CRM specimens appeared to show genetic structure between Mound 12 and Jacó Scar, with 3.2–3.6% COI divergence (uncorrected, corresponding to 17–19 bp) between localities and a maximum divergence of only < 0.2% (1 bp) within localities (Fig. 20H). We conservatively consider the Mound 12 and Jacó Scar populations to represent the same taxon, pending further sampling and morphological investigation. Yet we acknowledge the possibility of depth-segregated cryptic species, given that the depth-spanning sympatric scaleworm sister species Branchipolynoe halliseyae and B. kajsae are separated by a comparable COI distance (3.7% uncorrected) (Lindgren et al. 2019).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Terebellida | Terebelliformia | Terebellidae | Terebellini

Neoamphitrite cf. hydrothermalis Reuscher, Fiege & Wehe, 2012

Fig. 21A

Figure 21. 

Annelida: Terebellidae, Melinnidae, and Cirratulidae, representative live images A Neoamphitrite cf. hydrothermalis (A1351) B Neoamphitrite cf. robusta (A1456) C Melinnopsis cf. armipotens (A12604, in situ, tentacle protruding from the tube extending from the sediment and covered with hydroids, Co3088). Credit: ROV SuBastian/Schmidt Ocean Institute D Melinnopsis cf. armipotens (A12604) E Aphelochaeta sp. SIO_BIC_A1380 (A1380) F Aphelochaeta sp. SIO_BIC_A1380 (A1429) G Aphelochaeta sp. SIO_BIC_A9729 (A9729) H Chaetozone sp. SIO_BIC_A9846 (A9846). Scale bars: 1 mm (A, B, E–H); 1 cm (D).

Material examined. AD4504: A1351 (PQ450387).

Localities. Mound 11 (1010 m).

Remarks. Likely an undescribed species, morphologically similar to Neoamphitrite hydrothermalis, which is known from western Pacific hydrothermal vents in the Lihir Basin, 1474–1480 m (Reuscher et al. 2012). The COI sequence did not closely match any available GenBank reference sequences (<83% identity).

Neoamphitrite cf. robusta (Johnson, 1901)

Fig. 21B

Material examined. AD4512: A1456 (PQ450389); AD4588: A2150 (PQ449286).

Localities. Quepos Slide (400 m), Mound 12 (~ 995–997 m).

Remarks. Likely an undescribed species. Morphologically similar to Neoamphitrite robusta, which was described from shallow water in Puget Sound (Johnson 1901) and occurs in the eastern Pacific to depths of at least 1984 m (Hartman and Barnard 1958), including Pacific Costa Rica at 22 m (Wehrtmann and Cortés 2009b). The COI sequences did not closely match any available GenBank reference sequences (<81% identity).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Terebellida | Terebelliformia | Melinnidae

Melinnopsis cf. armipotens (Moore, 1923)

Fig. 21C, D

Material examined. S0220: A12604 (PQ449274).

Localities. Subduction Plume (3502 m).

Remarks. The tubes of these animals protruded above the sediment and were encrusted with Candelabrum hydroids (Co3088). They warrant comparison to Melinnopsis armipotens, known only from southern California, 4075 m (Moore 1923).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Cirratulida | Cirratulidae

We thank Jim Blake (Aquatic Research & Consulting) for morphological identification of these specimens. These specimens will be further discussed in a separate work.

Aphelochaeta sp. SIO_BIC_A1380

Fig. 21E, F

Material examined. AD4506: A1380 (PQ449000), AD4510: A1429.

Localities. Jacó Summit (741 m), Parrita Seep (1186 m).

Aphelochaeta sp. SIO_BIC_A9729

Fig. 21G

Material examined. AD4977: A9729 (PQ449323).

Localities. Jacó Scar (1783 m).

Remarks. Likely an undescribed species.

Chaetozone sp. SIO_BIC_A9846

Fig. 21H

Material examined. AD4987: A9846 (PQ449331).

Localities. Mound 12 (999 m).

Remarks. An undescribed species.

Cirratulus stet.

Fig. 22A

Figure 22. 

Annelida: Cirratulidae and Flabelligeridae, representative live images A Cirratulus stet. (A1435) B Raricirrus cf. maculatus (A1342) C Macrochaeta stet. (A8420) D Bradabyssa cf. pilosa (A9902) E Bradabyssa sp. SIO_BIC_A1356 (A1356) F Flabelligera cf. bophortica (A9751) G Lamispina polycerata (MZUCR 1504-01) H Saphobranchia canela (A9607). Scale bars: 1 cm (A, F); 1 mm (B–E, G, H).

Material examined. AD4510: A1435 (PQ449280); AD4912: A8303 (PQ449297); AD4973: A9677 (PQ449320); AD4989: A9907 (PQ449334), A9962 (PQ449339); S0213: A10051 (PQ449254).

Localities. Jacó Summit (~ 741–744 m), Jacó Scar (~ 1768–1811 m).

Remarks. Multiple species may be represented.

Raricirrus cf. maculatus Hartman, 1961

Fig. 22B

Material examined. AD4503: A1342 (PQ449276).

Localities. Mound 12 (990 m).

Remarks. Possibly Raricirrus maculatus, described from southern California, 46–70 m (Hartman 1961).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Cirratulida | Acrocirridae

Macrochaeta stet.

Fig. 22C

Material examined. AD4512: A1457; AD4918: A8420 (PQ449307); AD4985: A9854.

Localities. Quepos Slide (~ 338–411 m), Mound 12 (~ 995–1002 m).

Annelida | Polychaeta | Sedentaria | Canalipalpata | Cirratulida | Flabelligeridae

We thank Sergio Salazar-Vallejo (El Colegio de la Frontera Sur) for morphological identification of these specimens.

Bradabyssa cf. pilosa (Moore, 1906)

Fig. 22D

Material examined. AD4987: A9840 (PQ449330), A9902 (PQ449333).

Localities. Mound 12 (1010–1012 m).

Remarks. B. pilosa has been recorded from Alaska (type locality, 362–573 m) to Baja California, 40–1800 m, including seeps off Oregon and southern California (Salazar-Vallejo 2017). If confirmed as B. pilosa by genetic comparison to material from the type locality, the CRM specimens would represent a new southern record for the species. A9840 was associated with parasitic copepods (C14494), likely Bradophilidae.

Bradabyssa sp. SIO_BIC_A1356

Fig. 22E

Material examined. AD4504: A1356 (PQ449277); AD4590: A1962 (PQ450390).

Localities. Mound 11 (~ 1004–1011 m), Jacó Scar (~ 1791–1800 m).

Flabelligera cf. bophortica Annenkova-Chlopina, 1924

Fig. 22F

Material examined. AD4512: A1458; AD4976: A9751 (PQ449324).

Localities. Quepos Slide (~ 344–411 m), Jacó Scar (1887 m).

Remarks. These specimens resemble F. bophortica, which was described from the Chukchi Sea, Arctic Ocean, 13–48 m (Salazar-Vallego 2012). The main morphological difference is that in F. bophortica the dorsum is areolate, whereas in the CRM specimens it is smooth (Sergio Salazar-Vallejo, pers. comm. 12 February 2020). Specimen A9751 was associated with experimentally deployed wood.

Lamispina polycerata Salazar-Vallejo, 2020

Fig. 22G

Reference. Salazar-Vallejo 2020a**.

Localities. Mound 12 (999 m; type locality).

Distribution. Known only from the CRM seeps.

Saphobranchia canela Salazar-Vallejo, 2020

Fig. 22H

Reference. Salazar-Vallejo 2020a**.

Localities. Mound 12 (~ 987–997 m; type locality), Jacó Scar (1785 m).

Distribution. Known only from the CRM seeps.

Remarks. S. canela is distinguished from S. ilys and S. omorpha based on morphology, but genetic data do not corroborate the delineation of three species, as acknowledged in the original description (Salazar-Vallejo 2020a). The COI variation between specimens described as S. ilys and S. omorpha is less than the variation within S. canela (Fig. 23A). Collection of additional specimens and investigation of potential polymorphic conditions will be important for further work.

Figure 23. 

Annelida: Flabelligeridae, Paraonidae, and Sternaspidae, representative live images A haplotype network of COI sequences from the descriptions of Saphobranchia canela, S. ilys, and S. omorpha B Saphobranchia ilys (MZUCR 1503-01) C Saphobranchia omorpha (MZUCR 1501-01) D Aricidea mirifica (A1464) E Aricidea rubra (A10049) F Aricidea sp. A sec. Langeneck et al. 2019 (A1970) G Sternaspis stet. (A1473). Scale bars: 1 mm.

Saphobranchia ilys Salazar-Vallejo, 2020

Fig. 23B

Reference. Salazar-Vallejo 2020a**.

Localities. Jacó Scar (1783–1784 m; type locality).

Distribution. Known only from the CRM seeps.

Saphobranchia omorpha Salazar-Vallejo, 2020

Fig. 23C

Reference. Salazar-Vallejo 2020a**.

Localities. Jacó Scar (1795 m; type locality).

Distribution. Known only from the CRM seeps.

Annelida | Polychaeta | Sedentaria | Canalipalpata | Sternaspida | Paraonidae

Aricidea mirifica Strelzov, 1973

Fig. 23D

Reference. Langeneck et al. (2019) for DNA sequences and phylogenetic analysis, in which GenBank sequences MH700680 and MH688926 correspond to specimen A1464.

Material examined. AT15-44 MC1-2: A1464.

Localities. Near Mound 12 (1019 m).

Distribution. Also reported from shallow Pacific waters of Costa Rica, 18–26 m, as well as the eastern and western Pacific and Antarctic (Wehrtmann and Cortés 2009b).

Remarks. This specimen was collected in a sediment core adjacent to Mound 12, ca 500 m from known sites of active seepage and likely representing the far-transition zone to the surrounding environment.

Aricidea rubra Hartman, 1963

Fig. 23E

Reference. Langeneck et al. (2019) for DNA sequences and phylogenetic analysis, in which GenBank sequences MH700679, MH688925, and MH700708 correspond to specimen A1616 from Mound 12.

Material examined. AD4511: A1616; S0213: A10049 (PQ449252).

Localities. Jacó Summit (~ 730–820 m; this study), Mound 12 (988 m).

Distribution. Originally described from submarine canyons in southern California, 603–1298 m (Hartman 1963) and recorded from the South Atlantic, eastern and western Pacific, and Scotia Sea (Blake 1996).

Aricidea sp. A sec. Langeneck et al. 2019

Fig. 23F

Reference. Langeneck et al. (2019) for DNA sequences and phylogenetic analysis, in which GenBank sequences MH700686, MH688937, and MH700724 correspond to specimen A1970.

Material examined. AD4591: A1970.

Localities. Jacó Scar (~ 1752–1795 m).

Remarks. This specimen is an epitoke.

Annelida | Polychaeta | Sedentaria | Canalipalpata | Sternaspida | Sternaspidae

Sternaspis stet.

Fig. 23G

Reference. Drennan et al. (2019) for phylogenetic analysis.

Material examined. AT15-44 MC1-2: A1473 (16S: MK810080; 18S: MK809977); AD4989: A9943, A9945 (PQ449338), A9948.

Localities. Near Mound 12 (1019 m), Jacó Scar (1762 m; this study).

Remarks. Based on 16S and 18S sequences, specimen A1473 is phylogenetically distinct from its closest reported relative, the Antarctic species Sternaspis sendalli Salazar-Vallejo, 2014 (Drennan et al. 2019). Consistent with this result, the closest COI BLASTN results on GenBank for A9945 were specimens of S. sendalli (e.g., MK810006.1, NC_068907.1; up to 90.85% identity). A1473 was collected in a sediment core adjacent to Mound 12, ca 500 m from known sites of active seepage and likely representing the far-transition zone to the surrounding environment.

Annelida | Polychaeta | Sedentaria | Canalipalpata | Siboglinidae

Escarpia spicata Jones, 1985

Fig. 24A

Figure 24. 

Annelida: Siboglinidae and Orbiniidae, representative live images A Escarpia spicata (A8364) B Lamellibrachia barhami (A1564, incomplete specimens) C Lamellibrachia donwalshi (A8382) D Osedax frankpressi (A9592) E Osedax frankpressi (A9594, in bone) F Osedax knutei (A9617) G Siboglinum stet. (A8349) H Leitoscoloplos sp. SIO_BIC_A9939 (A9939). Scale bars: 1 cm (A–C); 1 mm (D–H).

References. Levin et al. (2012, 2015) for occurrences at Mound 12, Jacó Scar, and Parrita Seep.

Material examined. AD4503: A1343; AD4507: A1390 (PQ450388); AD4511: A1445; AD4513: A1463; AD4590: A1826; AD4591: A1838; AD4914: A8364; AD4924: A8464; AD4971: A9618, A9619, A9620, A9621, A9622, A9623, A9624, A9625, A9626, A9627; AD4987: A9901; S0217: A10089; S0230: A10172.

Localities. Mound 12 (~ 1000 m), The Thumb (1074 m; this study), Parrita Seep (~ 1400 m), Parrita Scar (~ 1600 m; this study), Jacó Scar (~ 1800 m), Mound Jaguar (1909 m; this study).

Distribution. Originally described from seeps at 1829 m in the San Clemente Basin off California (Karaseva et al. 2016), E. spicata has been reported as far south as northern Chile (Kobayashi and Araya 2018). It has been recorded from a range of reducing environments and depths, including a whale fall at 1240 m near the type locality (Feldman et al. 1998); sedimented vents and seeps at 1568–2020 m in the Guaymas Basin, Gulf of California (Black et al. 1997; Karaseva et al. 2016); and a seep at 2756 m in the Middle America Trench, off southern Mexico (Southward et al. 2002).

Remarks. The three described species of Escarpia (E. laminata Jones, 1985; E. southwardae Andersen et al., 2004; E. spicata Jones, 1985) are morphologically distinguishable with separate geographic ranges (Karaseva et al. 2016), but the most commonly used DNA sequence markers (COI, 16S, CytB) do not provide reliable differentiation among these species due to low sequence variation (Black et al. 1997; McMullin et al. 2003; Cowart et al. 2013). Alternative marker sequences, such as the nuclear hemoglobin subunit B2 intron (HbB2i), have been used to support the existing species designations, but resolving their phylogenetic relationships remains complex (Cowart et al. 2013; Kobayashi and Araya 2018). Nevertheless, all eastern Pacific occurrences of Escarpia are presently accepted as E. spicata (Karaseva et al. 2016).

Lamellibrachia barhami Webb, 1969

Fig. 24B

References. McMullin et al. 2003; Han et al. 2004; Mau et al. 2006; Sahling et al. 2008; Levin et al. 2012, 2015; McCowin and Rouse 2018.

Localities. Parrita Seep (~ 1400 m), Jacó Scar (~ 1800–1890 m), Parrita Scar (~ 2200 m).

Distribution. Originally described from seeps at 1125 m off southern California (Webb 1969), L. barhami occurs at seeps and sedimented vents (Middle Valley, Juan de Fuca Ridge; Pinkie’s “Vent,” Guaymas Basin), from Vancouver Island, Canada, to northern Chile, 1000–2400 m (Black et al. 1997, 1998; Bright and Lallier 2010; Karaseva et al. 2016; Kobayashi and Araya 2018; McCowin and Rouse 2018). The species shows only minimal COI divergence (<0.2%) across its range of more than 10,000 km (Kobayashi and Araya 2018; McCowin and Rouse 2018).

Lamellibrachia donwalshi McCowin & Rouse, 2018

Fig. 24C

Reference. McCowin and Rouse 2018**.

Localities. Mound 12 (~ 1000 m; type locality), Mound 11 (~ 1040 m).

Distribution. Known only from the CRM seeps.

Osedax frankpressi Rouse, Goffredi & Vrijenhoek, 2004

Fig. 24D, E

Reference. Berman et al. (2023) for DNA sequences and haplotype networks.

Material examined. AD4972: A9591 (OM994442), A9592 (OM994444), A9593 (OM994443), A9594 (OM994445).

Localities. Jacó Scar (1845 m).

Distribution. Originally described from Monterey Submarine Canyon off California (Rouse et al. 2004). Recorded in the eastern Pacific from the Oregon margin to the CRM as well as in the Atlantic off Brazil, 642–2891 m (Berman et al. 2023).

Remarks. Collected from experimentally deployed pig bones.

Osedax knutei Rouse, Goffredi, Johnson & Vrijenhoek, 2018

Fig. 24F

Reference. Berman et al. (2023) for DNA sequences and haplotype networks.

Material examined. AD4974: A9617 (ON041090).

Localities. Mound 12 (992 m).

Distribution. Monterey Submarine Canyon off California (type locality) to the CRM, 845–2898 m (Berman et al. 2023).

Remarks. Collected from experimentally deployed pig or cow bones.

Siboglinum stet.

Fig. 24G

Material examined. AD4911: A8349 (PQ449298); AD4916: A8388; AD4989: A9942.

Localities. Jacó Scar (~ 1757–1892 m).

Remarks. Collected from sediment cores, except for A8349 which was associated with a rock substrate. The occurrence of a field of frenulate siboglinids at Jacó Scar was noted by Levin et al. (2012).

Annelida | Polychaeta | Sedentaria | Orbiniida | Orbiniidae

Leitoscoloplos sp. SIO_BIC_A9939

Fig. 24H

Material examined. AD4989: A9939.

Localities. Jacó Scar (1785 m).

Remarks. This single damaged specimen likely represents an undescribed species (Jim Blake, pers. comm. 7 October 2019).

Annelida | Polychaeta | Sedentaria incertae sedis

Cossura stet.

Fig. 25A

Figure 25. 

Annelida: Cossura, Amphinomidae, Sipuncula, and Chaetopteridae, representative live images A Cossura stet. (A1388) B Amphinomidae stet. (A10107) C Amphinominae sp. SIO_BIC_A1379 (A1379) D Archinome levinae (A1398) E Sipuncula sp. SIO_BIC_A9803 (A9803) F Sipuncula sp. SIO_BIC_A9839 (A9839) G Phyllochaetopterus sp. 6 sec. Moore et al. 2017 (A1540) H Phyllochaetopterus sp. SIO_BIC_A8429 (A8429). Scale bars: 1 mm.

Material examined. AD4507: A1388; AD4988: A9922.

Localities. Mound 11 (~ 1005–1025 m), Parrita Scar (~ 1659–1663 m).

Annelida | Polychaeta | Amphinomida

Amphinomidae stet.

Fig. 25B

Material examined. S0219: A10107 (PQ449269).

Localities. Rio Bongo Scar (661 m).

Remarks. The COI sequence did not closely match any available GenBank reference sequences (<82% identity).

Amphinominae sp. SIO_BIC_A1379

Fig. 25C

Material examined. AD4506: A1379 (PQ300673).

Localities. Parrita Seep (1186 m).

Remarks. An undescribed genus and species. We thank Liz Borda (Texas A&M University San Antonio) for providing the COI sequence.

Archinome levinae Borda, Kudenov, Chevaldonné, Blake, Desbruyères, Fabri, Hourdez, Pleijel, Shank, Wilson, Schulze & Rouse, 2013

Fig. 25D

Reference. Borda et al. 2013**.

Localities. Mound 12 (~ 1000 m), Mound 11 (~ 1040 m; type locality), Parrita Seep (1402 m), Jacó Scar (~ 1800 m).

Distribution. Also known from vents in the Guaymas Basin, Gulf of California, ~ 2400 m (Borda et al. 2013).

Annelida | Polychaeta | Sipuncula

Sipuncula sp. SIO_BIC_A9803

Fig. 25E

Material examined. AD4978: A9803 (PQ449329).

Localities. Mound 12 (997 m).

Remarks. The closest COI BLASTN results on GenBank were an unidentified sipunculan from southern California (MK550656.1, 85.74% identity) and several golfingiids (~ 79–81% identity).

Sipuncula sp. SIO_BIC_A9839

Fig. 25F

Material examined. AD4987: A9839 (PQ450416).

Localities. Mound 12 (1012 m).

Remarks. Collected near a naturally occurring wood fall. The closest COI BLASTN results on GenBank were Nephasoma abyssorum (Koren & Danielssen, 1876) (JN865109.1, 82.14% identity) and several other golfingiids (~ 78–79% identity).

Annelida | Chaetopteriformia | Chaetopteridae

Phyllochaetopterus sp. 6 sec. Moore et al. 2017

Fig. 25G

Reference. Moore et al. (2017) for DNA sequences and phylogenetic analysis of specimen A1540.

Material examined. AD4501: A1324 (PQ449275); AD4505: A1540 (KX896487); AD4508: A1394; S0217: A10085 (PQ449263).

Localities. Mound 11 (~ 1019–1025 m), Mound 12 (~ 984–997 m; this study), The Thumb (~ 940–1070 m; this study), Parrita Seep (1402 m; this study).

Remarks. An undescribed species.

Phyllochaetopterus sp. SIO_BIC_A8429

Fig. 25H

Material examined. AD4922: A8429 (PQ449310); AD4988: A9916 (PQ449335), A9918 (PQ449336).

Localities. Mound 11 (1010 m), Mound 12 (1002 m).

Remarks. Associated with naturally occurring wood falls. Despite its sympatry with Phyllochaetopterus sp. 6 at Mound 12, this undescribed species is morphologically and genetically distinct, with a COI divergence of 14.89–15.41% from the previously published P. sp. 6 voucher SIO-BIC A1540 (KX896487.1). The closest COI BLASTN result on GenBank was an undescribed species of Spiochaetopterus from the East Pacific Rise (KX896501.1, voucher SIO-BIC A3619, 90.36–90.73% identity) (Moore et al. 2017). Phyllochaetopterus and Spiochaetopterus are not reciprocally monophyletic, and further phylogenetic investigation of their respective type species is required for revision of these genera (Moore et al. 2017).

Nemertea

We list higher-level taxonomy according to Strand et al. (2018).

Nemertea | Palaeonemertea | Tubulanidae

Tubulanus cf. lutescens Cantell, 2001

Fig. 26A

Figure 26. 

Nemertea, representative live images A Tubulanus cf. lutescens (N233) B Lineidae sp. SIO_BIC_N254 (N254) C Tetrastemma polyakovae (N258) D Tetrastemma sundbergi (N256) E Eumonostilifera sp. SIO_BIC_N109 (N109) F Alvinonemertes christianeae (N253) G Alvinonemertes dariae (N262) H Chernyshevia escarpiaphila (N266). Scale bars: 1 cm (A); 1 mm (B–H).

Reference. Sagorny et al. 2022.

Localities. Mound 11 (~ 1019–1025 m), Mound 12 (~ 982–998 m).

Remarks. Despite disparate geography and internal and external morphological differences, the CRM specimens show only 1.3% COI divergence from Tubulanus lutescens Cantell, 2001, known from shallow waters off Sweden, warranting further examination (Sagorny et al. 2022).

Nemertea | Pilidiophora | Heteronemertea | Lineidae

Lineidae sp. SIO_BIC_N254

Fig. 26B

Reference. Sagorny et al. 2022.

Localities. Jacó Scar (1887 m).

Remarks. Associated with experimentally deployed wood. This single specimen (destroyed for DNA extraction) could not be attributed to a known genus and likely represents an undescribed species (Sagorny et al. 2022).

Nemertea | Hoplonemertea | Monostilifera | Amphiporina

Tetrastemma polyakovae Sagorny, von Döhren, Rouse & Tilic, 2022

Fig. 26C

Reference. Sagorny et al. 2022**.

Localities. Mound 12 (~ 996–999 m; type locality).

Distribution. Known only from the CRM seeps.

Tetrastemma strandae Sagorny, von Döhren, Rouse & Tilic, 2022

Reference. Sagorny et al. 2022** (histological sections published; no live images captured).

Localities. Jacó Scar (1885 m; type locality).

Distribution. Known only from the CRM seeps.

Tetrastemma sundbergi Sagorny, von Döhren, Rouse & Tilic, 2022

Fig. 26D

Reference. Sagorny et al. 2022**.

Localities. Mound 12 (~ 996–999 m; type locality).

Distribution. Known only from the CRM seeps.

Nemertea | Hoplonemertea | Monostilifera | Eumonostilifera

Eumonostilifera sp. SIO_BIC_N109

Fig. 26E

Reference. Sagorny et al. 2022.

Localities. Parrita Seep (~ 1401–1419 m).

Remarks. An undescribed species represented by a single specimen (Sagorny et al. 2022).

Nemertea | Hoplonemertea | Monostilifera | Oerstediina

Alvinonemertes christianeae Sagorny, von Döhren, Rouse & Tilic, 2022

Fig. 26F

Reference. Sagorny et al. 2022**.

Localities. Jacó Scar (1887 m; type locality).

Distribution. Also reported from the non-seep seamount Quepos Plateau, 67 km south of Jacó Scar, at 2184 m depth.

Remarks. Associated with experimentally deployed or naturally occurring wood (Sagorny et al. 2022).

Alvinonemertes dariae Sagorny, von Döhren, Rouse & Tilic, 2022

Fig. 26G

Reference. Sagorny et al. 2022**.

Localities. Parrita Seep (1407 m; type locality).

Distribution. Known only from the CRM seeps.

Remarks. Associated with Paragorgia stet. (Co3054) (Sagorny et al. 2022).

Chernyshevia escarpiaphila Sagorny, von Döhren, Rouse & Tilic, 2022

Fig. 26H

Reference. Sagorny et al. 2022**.

Localities. Jacó Scar (~ 974–1856 m), Mound Jaguar (1909 m; type locality).

Distribution. Known only from the CRM seeps.

Remarks. Associated with the exterior surfaces and tubes of Escarpia spicata (Sagorny et al. 2022).

Brachiopoda

Platidia anomioides (Scacchi & Philippi in Philippi, 1844) sp. inc.

Fig. 27A, B

Figure 27. 

Brachiopoda and Mollusca: Bivalvia: Nuculidae, Solemyidae, and Nuculanidae, representative live images A Platidia anomioides sp. inc. (B211, exterior view) B Platidia anomioides sp. inc. (B211, interior view) C Ennucula colombiana (M17879) D Ennucula stet. (M16966) E Nucula chrysocoma (M11989) F Acharax cf. johnsoni (M15768, adult specimen, opened) G Acharax cf. johnsoni (M17077, young specimen) H Nuculana cf. callimene (M17063). Scale bars: 1 mm (A–E, H); 1 cm (F, G).

Material examined. AD4512: B211; AD4979: M16876.

Localities. Quepos Slide (~ 380–395 m).

Remarks. We thank Sandra Carlson (University of California Davis) for the identification of these specimens as Platidia, most likely P. anomioides, which is considered cosmopolitan at depths 18–2190 m (Foster 1989; Santagata and Tunnell 2009). More definitive identification requires dissolving soft tissues for analysis of the cardinalia and spicules. At least one specimen contains eggs in the mantle canals (Fig. 27B).

Mollusca

We list the major clades according to the phylogenetic relationships in Smith et al. (2011).

Mollusca | Bivalvia

We list entries following the taxonomic arrangement in Valentich-Scott et al. (2020).

Mollusca | Bivalvia | Protobranchia | Nuculida | Nuculidae

Ennucula colombiana (Dall, 1908)

Fig. 27C

Material examined. AD4588: M17879.

Localities. Mound 12 (997 m).

Distribution. Originally described from the Gulf of Panama, 54 m, and known from the Gulf of California to Peru, 11–734 m (Coan and Valentich-Scott 2012).

New records. The CRM specimen represents a new maximum depth record for this species.

Ennucula stet.

Fig. 27D

Material examined. AD4988: M16966 (PQ449418).

Localities. Mound 11 (1010 m).

Remarks. This damaged juvenile specimen was associated with a naturally occurring wood fall. The closest COI BLASTN results on GenBank were nuculids: Ennucula cumingii (Hinds, 1843) (KC984750.1, 84.89% identity), E. tenuis (Montagu, 1808) from Japan (LC144804.1, 83.23% identity), E. niponica (E. A. Smith, 1885) from Japan (LC144803.1, 83.10% identity), and Acila mirabilis (A. Adams & Reeve, 1850) from Japan (LC144802.1, 83.36% identity).

Nucula chrysocoma Dall, 1908

Fig. 27E

Material examined. AD4503: M11989.

Localities. Mound 12 (~ 965–995 m).

Distribution. Originally described from several stations off Peru, Ecuador, and southern Mexico, 734–4064 m (Dall, 1908), and known from Cascadia Abyssal Plain, Oregon, to Coquimbo, central Chile, 734–4134 m (Valentich-Scott et al. 2020).

Mollusca | Bivalvia | Protobranchia | Solemyida | Solemyidae

Acharax cf. johnsoni (Dall, 1891)

Fig. 27F, G

References. Neulinger et al. (2006) for DNA sequences and phylogenetic analysis; occurrences at Mound 11 and Mound 12 (Aguado and Rouse 2011; Levin et al. 2015; Rouse et al. 2018).

Additional material examined. AD4503: M11980; AD4505: M12003; AD4507: M12012 (juvenile); AD4511: M12054, M16239; AD4513: M12072; AD4910: M15768 (18S: PQ304648), M15769; S0217: M17062; S0220: M17077 (18S: PQ304649; juvenile).

Localities. Mound 12 (~ 1000 m), Mound 11 (~ 1020 m), The Thumb (1069 m; this study), Parrita Scar (~ 1659–1663 m; this study), Jacó Scar (1744 m; this study), Subduction Plume (3410 m; this study). The collection locality in Neulinger et al. (2006) (9°10.4'N, 084°48.2'W, 763 m) matches the site referenced in this work as Jacó Summit.

Remarks. Originally described from 1838 m off Baja California (Dall 1891), A. johnsoni has been reported along the eastern Pacific margin from Alaska to Peru, as well as in the northwestern Pacific, 100–5379 m (Coan and Valentich-Scott 2012). According to 18S phylogenies, at least two clades of deep-sea Acharax, morphologically similar to A. johnsoni, occur in the Pacific and warrant consideration as separate species (Neulinger et al. 2006; Fukasawa et al. 2017). In the absence of genetic data from the type locality (only empty shells have been recovered from recent expeditions to the region (Hendrickx et al. 2016; Suárez-Mozo et al. 2019)), we report the CRM specimens as A. cf. johnsoni.

The two 18S sequences in this study matched different previously reported clades, suggesting the presence of at least two cryptic species at the CRM, potentially segregated by depth. M17007 from Subduction Plume (3410 m) showed 99.94% identity to the Jacó Summit specimen (AJ563763.1) in Neulinger et al. (2006). M17007 also grouped with the “Acharax 1” clade of (Fukasawa et al. 2017), showing 99.61–99.94% identity to sequences from the Aleutian Trench (AJ563760.1), Java Trench (AJ563756.1, AJ563757.1), Chishima Trench seeps (LC186962.1), Japan Trench seeps (LC186965.1, LC186966.1), Hine Hina vents in the Lau Basin (LC186970.1), and Haima seeps (OQ836650.1). M15768 from Mound 12 (~ 1000 m) grouped with the “Acharax 2” clade of Fukasawa et al. (2017), showing 99.14–99.77% identity to sequences from seeps off Oregon (AJ563751.1, AJ563752.1, AJ563753.1, AJ563754.1, AJ563755.1), off Peru (AJ563762.1), and at the Nankai Trough (LC186957.1). The “Acharax 1” and “Acharax 2” clades show the same depth range globally (765–5300 m and 780–5300 m, respectively) (Fukasawa et al. 2017), so further sequencing and sampling are needed to assess depth stratification of Acharax at the CRM. A detailed comparison of these clades may also illuminate distinguishing morphological features.

CRM specimens from Mound 11 and Mound 12 are hosts of copepods (see Cyclopoida sp. SIO_BIC_C12780), the chrysopetalid Natsushima sashai (Aguado and Rouse 2011), and the hesionid Neogyptis jeffruoccoi (Rouse et al. 2018).

Mollusca | Bivalvia | Protobranchia | Nuculanida | Nuculanidae

Nuculana cf. callimene (Dall, 1908)

Fig. 27H

Material examined. S0220: M17063.

Localities. Subduction Plume (3434 m).

Remarks. This specimen is morphologically similar to N. callimene except for the posterior end and may represent an undescribed species. N. callimene is known from western Baja California to the Pacific margin of Panama (type locality), 183–3200 m (Coan and Valentich-Scott 2012; Hendrickx et al. 2016).

Nuculana cf. hamata (Carpenter, 1864)

Fig. 28A

Figure 28. 

Mollusca: Bivalvia: Nuculanidae, Bathyspinulidae, Yoldiidae, and Mytilidae, representative live images A Nuculana cf. hamata (M12047) B Tindariopsis grasslei (M16806) C Yoldiella stet. (M12046) D Bathymodiolus billschneideri (M12074) E Bathymodiolus earlougheri (M14479) F Bathymodiolus nancyschneiderae (M14531) G Bathymodiolus thermophilus (M17023) H Idas stet. (M17069). Scale bars: 1 mm (A–C, H); 1 cm (D–G).

Material examined. AD4510: M12047.

Localities. Jacó Summit (742 m).

Remarks. This specimen resembles N. hamata, which is known from Alaska to the Gulf of California (type locality: Catalina Island, southern California), 20–1100 m, and may include cryptic species; records of this morphologically variable species from further south are considered suspect and warrant further investigation (Coan and Valentich-Scott 2012; Hendrickx et al. 2016). Genetic comparison to N. cf. hamata recorded from Baja California, 750–850 m (Hendrickx et al. 2016), may be informative.

Mollusca | Bivalvia | Protobranchia | Nuculanida | Bathyspinulidae

Tindariopsis grasslei (Allen, 1993)

Fig. 28B

Material examined. AD4503: M11985 (dead shell only); AD4506: M12005; AD4590: M12141; AD4971: M16735, M16736; AD4973: M16749, M16750; AD4977: M16806; AD4987: M16902; AD4985: M16908; AD4988: M16964; S0217: M17042.

Localities. Mound 12 (990 m, dead shell; 992–1010 m, live specimens), Mound 11 (1009 m), Parrita Seep (~ 1030–1179 m), The Thumb (1069 m), Jacó Scar (1783–1817 m).

Distribution. Known from the Guaymas Basin, Gulf of California (type locality, 2003 m), to the Costa Rica Subduction Zone, 1400–2012 m (Coan and Valentich-Scott 2012).

New records. CRM specimen M16908 from 992 m represents a new minimum depth for this species.

Remarks. This species is placed “with reluctance” in Tindariopsis (Coan and Valentich-Scott 2012). Preliminary molecular work suggests a position closer to Malletia. M11985 was associated with a naturally occurring wood fall.

Mollusca | Bivalvia | Protobranchia | Nuculanida | Yoldiidae

Yoldiella stet.

Fig. 28C

Material examined. AD4510: M12046.

Localities. Jacó Summit (742 m).

Mollusca | Bivalvia | Pteriomorphia | Mytilida | Mytilidae

Bathymodiolus billschneideri McCowin, Feehery & Rouse, 2020

Fig. 28D

Reference. McCowin et al. 2020**.

Localities. Parrita Seep (~ 1400 m), Jacó Scar (~ 1750–1900 m; type locality).

Distribution. Known only from the CRM seeps and apparently found no shallower than ~ 1400 m.

Remarks. B. billschneideri is a host of the scaleworms Branchipolynoe eliseae, Br. halliseyae, Br. kajsae, and Br. meridae (Lindgren et al. 2019). Previous reports of mytilid mussels at Parrita Seep (previously published as “Quepos Seep”) (Sahling et al. 2008) and brown-colored Bathymodiolus mussels at Jacó Scar (Levin et al. 2012, 2015) are now known to correspond to B. billschneideri.

Bathymodiolus earlougheri McCowin, Feehery & Rouse, 2020

Fig. 28E

Reference. McCowin et al. 2020**.

Localities. Mound 12 (~ 1000 m), The Thumb (1073 m), Jacó Scar (~ 1750–1900 m; type locality).

Distribution. Known only from the CRM seeps.

Remarks. B. earlougheri likely also occurs at sites of intermediate depth (e.g., Parrita Seep, ~ 1400 m) but has not been collected there, likely due to limited sampling (McCowin et al. 2020). B. earlougheri is the only known host of the chrysopetalid Laubierus alvini (Aguado and Rouse 2011). It is also a host of the scaleworms Branchipolynoe halliseyae, Br. kajsae, Br. meridae, and possibly Br. eliseae (Lindgren et al. 2019). Previous reports of golden-colored Bathymodiolus mussels at multiple CRM seep sites (Levin et al. 2012, 2015) are now known to correspond to B. earlougheri.

Bathymodiolus nancyschneiderae McCowin, Feehery & Rouse, 2020

Fig. 28F

Reference. McCowin et al. 2020**.

Localities. Mound 12 (~ 1000 m), Jacó Slope (1063 m; type locality), The Thumb (1073 m).

Distribution. Known only from the CRM seeps and apparently found no deeper than ~ 1000 m.

Remarks. B. nancyschneiderae is a host of the scaleworms Branchipolynoe eliseae, Br. halliseyae, Br. kajsae, and possibly also Br. meridae (Lindgren et al. 2019). Previous reports of brown-colored Bathymodiolus spp. at Mound 11 and Mound 12 (Levin et al. 2015) are now known to correspond to B. nancyschneiderae.

Bathymodiolus thermophilus Kenk & B. R. Wilson, 1985

Fig. 28G

References. Levin et al. 2012; McCowin et al. 2020.

Localities. Jacó Scar (1794–1814 m).

Distribution. Originally described from 2495 m at the Galápagos Rift (Kenk and Wilson 1985) and distributed along the East Pacific Rise between 13°N and 21°S latitude (Johnson et al. 2013), B. thermophilus was previously thought to be restricted to hydrothermal vents but also occurs at the Jacó Scar “hydrothermal seep” site (Levin et al. 2012; McCowin et al. 2020).

Remarks. B. thermophilus specimens from the CRM seeps were not observed to contain Branchipolynoe spp. scaleworms, but this apparent absence may reflect limited sample size and the tendency of the worms to evacuate the mussels upon disturbance.

Idas stet.

Fig. 28H

Reference. Xu et al. (2017) for phylogenetic analysis.

Material examined. AD4587: M13006 (KU975037); AD4907: M16100; S0219: M17069 (PQ450399).

Localities. Rio Bongo Scar (661 m; this study), Mound 12 (996–999 m).

Remarks. Associated with naturally occurring and experimentally deployed wood. As described in Xu et al. (2017), M13006 shows morphological similarity to Idas washingtonius (Bernard, 1978), which occurs in the eastern Pacific from Washington to the Guaymas Basin and in the western Pacific, 1240–2200 m (Coan et al. 2000), but genetically it is more closely related to I. macdonaldi Gustafson, Turner, Lutz & Vrijenhoek, 1998, which occurs at hydrocarbon seeps in the Gulf of Mexico (Gustafson et al. 1998). The paraphyly of Idas (Lorion et al. 2013; Xu et al. 2017) warrants further investigation.

Mollusca | Bivalvia | Pteriomorphia | Pectinida | Pectinidae

Delectopecten vancouverensis (Whiteaves, 1893)

Fig. 29A

Figure 29. 

Mollusca: Bivalvia: Pectinidae, Thyasiridae, Galeommatidae, and Vesicomyidae, representative live images A Delectopecten vancouverensis (M16184) B Delectopecten zacae (M16188) C Thyasira methanophila (M17098, valve only) D Thyasira stet. (M12059) E Axinodon cf. redondoensis (M16845) F Archivesica gigas (M12011) G Archivesica sp. 6 sec. Audzijonyte et al. 2012 (M16141) H Archivesica sp. SIO_BIC_M12070 aff. gigas (M12070). Scale bars: 1 mm (A–E); 1 cm (F–H).

Material examined. AD4512: M12063; AD4918: M16184.

Localities. Quepos Slide (338–~ 400 m).

Distribution. Originally described from British Columbia, Canada; recorded in the eastern Pacific from Alaska to Baja California as well as the Bering Sea and northwestern Pacific to the Sea of Japan, 20–4100 m (Coan and Valentich-Scott 2012; Kamenev 2013; Hendrickx et al. 2016). GBIF includes a museum record from the Galápagos Islands, 466 m (Blum and Fong 2016c).

New records. Pending verification of the GBIF record, the CRM specimens represent new southern records for this species.

Remarks. M16184 was associated with epibiotic hydroids. DNA sequences could not be obtained.

Delectopecten zacae (Hertlein, 1935)

Fig. 29B

Material examined. AD4921: M16188.

Localities. Quepos Slide (~ 345–394 m).

Distribution. Known from Baja California (type locality: Cabo San Lucas, 37–402 m) (Hertlein 1935), to Peru and the Galápagos Islands, 10–1840 m (Coan and Valentich-Scott 2012).

Remarks. DNA sequences could not be obtained.

Mollusca | Bivalvia | Heterodonta | Lucinida | Thyasiridae

Thyasira methanophila P. G. Oliver & Sellanes, 2005

Fig. 29C

Reference. Coan and Valentich-Scott (2012), in which the locality of specimen SBMNH 350533 (9.033, -84.621; 1408 m; no DNA sequences; Santa Barbara Museum of Natural History) aligns with the locality known in this work as Parrita Seep.

Additional material examined. S0230: M17098 (juvenile specimen, only valves collected).

Localities. Parrita Seep (1408 m); Mound Jaguar (1909 m; this study, valves).

Distribution. Also known from seeps at the type locality off Concepción, central Chile, 780 m (Oliver and Sellanes 2005). Confirmation of live specimens at Mound Jaguar would establish a new depth record.

Thyasira stet.

Fig. 29D

Material examined. AD4512: M12059 (PQ450412); AD4978: M16840; AD4988: M16977.

Localities. Quepos Slide (~ 344–411 m), Mound 12 (~ 996–999 m), Jacó Scar (1783 m).

Remarks. This morphospecies warrants comparison to other eastern Pacific specimens that have been dubiously reported as Thyasira flexuosa (Montagu, 1803) (type locality: Great Britain) and likely represent several cryptic species (Coan et al. 2000; Coan and Valentich-Scott 2012). For M12059, the closest COI BLASTN results on GenBank were Thyasira sarsii (R. A. Philippi, 1845) from Norway (AM706508.1 and AM706509.1, both 97.09% identity). Based on a recent phylogeny (Fukasawa et al. 2017), Thyasira appears to require taxonomic revision.

Mollusca | Bivalvia | Heterodonta | Galeommatida | Galeommatidae

Axinodon cf. redondoensis (T. A. Burch, 1941)

Fig. 29E

Material examined. AD4978: M16845.

Localities. Mound 12 (~ 996–999 m).

Remarks. Likely an undescribed species. Possibly a range and depth extension of Axinodon redondoensis, presently known from Washington to Redondo Beach, southern California (type locality, 137 m), 120–330 m (Harry 1969; Valentich-Scott 1998; Coan et al. 2000).

Mollusca | Bivalvia | Heterodonta | Venerida | Vesicomyidae

We thank Elena Krylova (P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences) for input on this section.

Archivesica gigas (Dall, 1896)

Fig. 29F

References. Audzijonyte et al. 2012; Levin et al. 2012.

Additional material examined. AD4506: M12007; AD4507: M12011 (PQ449002); AD4508: M12014 (PQ449401).

Localities. Parrita Seep (1186 m, ~ 1400 m; this study), Parrita Scar (~ 1659–1667 m; this study), Jacó Scar (~ 1800 m); an unnamed locality ~ 85 km northwest of Mound Jaguar (10.3000, -86.3053; 1531 m) (Audzijonyte et al. 2012).

Distribution. Originally described from the Guaymas Basin, Gulf of California, 1567 m (Dall 1896) and reported as far north as the Gulf of Alaska (Coan and Valentich-Scott 2012). Genetically confirmed records are known from seeps, sedimented vents, and whale falls from the Oregon Subduction Zone to Costa Rica, 1013–2028 m, as well as a seep at 1200 m in Hiroo Submarine Canyon off Hokkaido (Audzijonyte et al. 2012).

Archivesica sp. 6 sec. Audzijonyte et al. 2012

Fig. 29G

Reference. Audzijonyte et al. (2012) for DNA sequences and phylogenetic analysis.

Additional material examined. AD4590: M13509 (PQ450381, PQ450398; tissues); AD4912: M16141 (PQ449413).

Localities. Jacó Scar (1677 m; ~ 1791–1842 m, this study).

Distribution. Known only from the CRM seeps.

Remarks. Morphologically resembles A. gigas and may warrant description as a new species (Audzijonyte et al. 2012).

Archivesica sp. 7 sec. Audzijonyte et al. 2012

References. Peek et al. (2000) and Audzijonyte et al. (2012) for DNA sequences and phylogenetic analysis. Not collected in this study.

Localities. An unnamed seep at 3002 m (9.69850, -86.06817) and a “low-temperature vent” at 3096 m (9.7112, -86.0777) (Audzijonyte et al. 2012), both ~ 20 km west of Mound Jaguar.

Distribution. Also known from a seep at 4300 m in the Middle America Trench off Mexico (Audzijonyte et al. 2012; Decker et al. 2012) and from the Peru margin, 3711–4724 m (Audzijonyte et al. 2012).

Remarks. This taxon warrants consideration as a new species based on COI sequences, but no morphological voucher specimens are available (Audzijonyte et al. 2012).

Archivesica sp. SIO_BIC_M12070 aff. gigas (Dall, 1896)

Fig. 29H

Material examined. AD4513: M12070 (PQ450402).

Localities. Jacó Scar (1744 m).

Remarks. An undescribed species. The COI sequence of this specimen was 94.83–95.20% identical to sequences of A. gigas from northern Japan (PP899629.1), the Guaymas Basin, Gulf of California (MF959623.1 (Liu et al. 2018), MT947383.1), and off northern California (MT947382.1).

Calyptogena costaricana Krylova & Sahling, 2006

Reference. Krylova and Sahling 2006**. Not collected in this study.

Localities. Mound 10 (2258–2263 m; type locality).

Distribution. Also known from seeps in Monterey Canyon, off California, 2193–2219 m, and a vent on the Peru margin, 2500 m (Audzijonyte et al. 2012).

Calyptogena diagonalis Barry & Kochevar, 1999

Fig. 30A

Figure 30. 

Mollusca: Bivalvia: Vesicomyidae, Xylophagaidae, and Teredinidae, representative live images A Calyptogena diagonalis (M17064) B Phreagena soyoae (M11999) C Phreagena sp. 5 sec. Audzijonyte et al. 2012 (M12009) D Pliocardia krylovata (M17026) E Xylophaga stet. (M16099) F Xyloredo gen. inc. (M17870) G Teredinidae sp. SIO_BIC_M17100 (M17100) H Teredinidae stet. (M12290). Scale bars: 1 cm (A–D); 1 mm (E–H).

References. Barry and Kochevar 1999**; Audzijonyte et al. 2012.

Additional material examined. S0220: M17064, M17065.

Localities. Subduction Plume (3408 m; this study); an unnamed seep (9°42.28'N, 86°4.38'W; 2980–3800 m; type locality) (Barry and Kochevar 1999) and a “low-temperature vent” (9.7112, -86.0777; 3096 m) (Audzijonyte et al. 2012), both ~ 20 km west of Mound Jaguar.

Distribution. Also known from seeps at the Oregon margin, 2021–2089 m (Barry and Kochevar 1999; Audzijonyte et al. 2012; Coan and Valentich-Scott 2012), vents at the Juan de Fuca Ridge, 2400–2437 m (Peek et al. 1997; Audzijonyte et al. 2012), and the Peru margin, 2290–3070 m (Audzijonyte et al. 2012).

Remarks. M17065 was associated with an anemone, Co3084. Based on morphological and genetic similarities, Audzijonyte et al. (2012) recommend synonymization of this species (referenced as Archivesica diagonalis) with the western Pacific nominal species A. magnocultellus (Okutani, Kojima & Iwasaki, 2002), pending examination of the type material of A. magnocultellus. Formal synonymization would extend the species’ range to seeps off southern Japan, 1900–2500 m (Audzijonyte et al. 2012).

Calyptogena sp. 3 sec. Audzijonyte et al. 2012

Reference. Audzijonyte et al. (2012) for DNA sequences and phylogenetic analysis. Not collected in this study.

Localities. Unnamed seep ~ 25 km west of Mound Jaguar (9.6678, -86.1193; 3560 m) (Audzijonyte et al. 2012).

Distribution. Also known from seep and whale fall habitats off central California, 2895–3449 m (Audzijonyte et al. 2012).

Remarks. This taxon warrants consideration as a new species based on COI sequences, but no morphological voucher specimens are available (Audzijonyte et al. 2012).

Calyptogena sp. mt-V sec. Goffredi et al. 2003

References. Goffredi et al. (2003) and Audzijonyte et al. (2012) for DNA sequences and phylogenetic analysis. Not collected in this study.

Localities. Unnamed “low-temperature vent” ~ 20 km west of Mound Jaguar (9.7112, -86.0777; 3096 m) (Audzijonyte et al. 2012).

Remarks. The single genetic sample of this taxon was originally identified as Calyptogena pacifica (Peek et al. 2000) and underwent several nomenclatural revisions upon further phylogenetic analyses (Goffredi et al. 2003; Audzijonyte et al. 2012). This taxon warrants consideration as a new species based on COI sequences, but no morphological voucher specimens are available (Audzijonyte et al. 2012).

Phreagena extenta (Krylova & Moskalev, 1996)

Reference. Peek et al. (2000) for DNA sequences and phylogenetic analysis. Not collected in this study.

Localities. Unnamed seep ~ 20 km west of Mound Jaguar (9.6983, -86.0682; 3002 m).

Distribution. Originally described from a seep in Monterey Bay at 3041 m; recorded from the Gulf of Alaska to Costa Rica, 2889–4445 m (Peek et al. 2000; Audzijonyte et al. 2012; Coan and Valentich-Scott 2012), as well as the Kuril Trench, 3512 m (Okutani et al. 2009; Audzijonyte et al. 2012).

Remarks. Previously placed in Ectenagena and then Calyptogena (Coan and Valentich-Scott 2012), this species is provisionally, and with an acknowledgment of doubt, allocated to Phreagena (Johnson et al. 2017).

Phreagena soyoae (Okutani, 1957)

Fig. 30B

Reference. Audzijonyte et al. (2012) for DNA sequences and phylogenetic analysis.

Additional material examined. AD4505: M11999 (PQ449397, PQ449398, PQ449399, PQ450407, PQ450408).

Localities. Mound 11 (~ 1019-1025 m; this study); Mound Carablanca, Nicaragua margin (1432 m).

Distribution. Originally described from seeps off Japan, 750–1500 m (type locality: Sagami Bay, 750 m), P. soyoae is found at seep, vent, and whale fall habitats from the Juan de Fuca Ridge to the Costa Rica and Nicaragua margins, 519–2400 m (Audzijonyte et al. 2012).

Phreagena sp. 5 sec. Audzijonyte et al. 2012

Fig. 30C

Reference. Audzijonyte et al. (2012) for DNA sequences and phylogenetic analysis.

Additional material examined. AD4506: M12009 (PQ449400), M12085 (PQ450380); AD4508: M12088 (PQ450379); AD4988: M16960 (PQ449417).

Localities. Mound 11 (1012 m; this study), Jacó Slope (1024 m), Parrita Seep (1186 m and ~ 1400 m, this study; 1408 m). The locality “Mound Quepos” at 1408 m and the upslope region of Jacó Scar at 1024 m in Audzijonyte et al. (2012) are reported as “Parrita Seep” and “Jacó Slope,” respectively, in this work.

Remarks. Morphologically resembles Phreagena soyoae and may warrant description as a new species (Audzijonyte et al. 2012).

Pliocardia krylovata A. M. Martin & Goffredi, 2012

Fig. 30D

Reference. Martin and Goffredi 2012**.

Additional material examined. S0213: M17026.

Localities. Jacó Summit (~ 741–744 m; type locality), Mound 12 (~ 967–995 m).

Distribution. Known only from the CRM seeps.

Remarks. Found in sediments near microbial mats and typically positioned with approximately half the shell length above the sediment, forming “a spatial bridge between the oxic overlying water and the sulphide-rich sediment” (Martin and Goffredi 2012). Assignment of this species to the genus Pliocardia was tentative based on uncertainty within Pliocardiinae (Martin and Goffredi 2012), and the clade containing this taxon was later suggested to warrant a new genus (Johnson et al. 2017).

Mollusca | Bivalvia | Heterodonta | Myida | Pholadoidea | Xylophagaidae

Xylophaga stet.

Fig. 30E

Material examined. AD4906: M15767, M16099, M16111.

Localities. Mound 12 (1002 m).

Remarks. Associated with experimentally deployed wood. We thank Chiara Romano (University of Gastronomic Sciences) for this identification.

Xyloredo gen. inc.

Fig. 30F

Material examined. AD4588: M17870.

Localities. Mound 12 (~ 1000 m).

Remarks. Associated with a naturally occurring palm wood fall.

Mollusca | Bivalvia | Heterodonta | Myida | Pholadoidea | Teredinidae

We thank Reuben Shipway (University of Plymouth) for these identifications.

Teredinidae sp. SIO_BIC_M17100

Fig. 30G

Material examined. AD4913: M16147; S0230: M17100 (PQ449424).

Localities. Jacó Scar (1817 m), Mound Jaguar (1896 m).

Remarks. An undescribed species associated with naturally occurring wood falls.

Teredinidae stet.

Fig. 30H

Material examined. AD4588: M12290.

Localities. Mound 12 (995 m).

Remarks. Associated with a naturally occurring wood fall. DNA sequences could not be obtained.

Mollusca | Bivalvia | Heterodonta | Anomalodesmata | Cuspidariidae

Bathyneaera tillamookensis (Dall, 1916)

Fig. 31A

Figure 31. 

Mollusca: Bivalvia and Gastropoda: Patellogastropoda, representative live images A Bathyneaera tillamookensis (M16982) B Luzonia chilensis (M16808) C Iothia stet. (M16172, separate specimens in dorsal and lateral view) D Iothia stet. (M16173, separate specimens in dorsal and lateral view) E Eulepetopsis gen. inc. (M17882, dorsal view) F Eulepetopsis gen. inc. (M17882, ventral view) G Neolepetopsidae stet. (M11963, dorsal view) H Neolepetopsidae stet. (M11963, ventral view). Scale bars: 1 mm.

Material examined. AD4989: M16982.

Localities. Jacó Scar (1762 m).

Distribution. Originally described from the Oregon margin, 1438 m, and known from British Columbia, Canada, to Peru as well as the Atlantic and New Zealand, 439–2850 m (Coan and Valentich-Scott 2012).

Luzonia chilensis (Dall, 1890)

Fig. 31B

Material examined. AD4508: M12026; AD4974: M16769; AD4977: M16808; AD4989: M16980, M16981, M16983.

Localities. Mound 12 (990 m), Parrita Seep (1402 m), Jacó Scar (1762–1783 m).

Distribution. Originally described from Isla Mocha, central Chile, 1238 m, and known from the U.S. Pacific coast off Washington to southern Chile, 100–1875 m (Coan and Valentich-Scott 2012).

Mollusca | Gastropoda

We list the six widely accepted major gastropod clades (Bouchet et al. 2017) in a sequence reflecting their current phylogenomic relationships (Uribe et al. 2022; Zhong et al. 2022), acknowledging the possibility of further revision of higher-level clade names. Within these clades we organize the listings following WoRMS. We recognize the need for considerable further taxonomic and genetic work, especially on limpet-shaped forms such as Neolepetopsidae and Cocculiniformia (Desbruyères et al. 2006; Chen et al. 2019b, 2023). Several gastropod morphospecies occurring at Jacó Scar were provisionally identified in Electronic supplemental table S6 of Levin et al. (2012) and are here linked to voucher specimens where possible.

Mollusca | Gastropoda | Patellogastropoda | Lottioidea | Lepetidae

Iothia stet.

Fig. 31C, D

Reference. Electronic supplemental table S6 of Levin et al. (2012) (occurrences only, Jacó Scar).

Material examined. AD4508: M12025 (PQ450378); AD4916: M16172, M16173.

Localities. Parrita Seep (~ 1401–1419 m), Jacó Scar (1611 m).

Remarks. For M12025, the closest COI BLASTN results on GenBank were specimens of Iothia fulva (O. F. Müller, 1776) from the North Sea (KR084663.1, KR084581.1; 94.53% identity).

Mollusca | Gastropoda | Patellogastropoda | Lottioidea | Neolepetopsidae

Eulepetopsis gen. inc.

Fig. 31E, F

Reference. Electronic supplemental table S6 of Levin et al. (2012) as Eulepetopsis sp. (occurrences only, Jacó Scar).

Material examined. AD4506: M12004; AD4590: M17882, M18921, M19153.

Localities. Parrita Seep (1186 m), Jacó Scar (~ 1800 m).

Remarks. Morphologically similar to Eulepetopsis, although the two described species of Eulepetopsis are known only from high-temperature vents and Neolepetopsidae may require revision (Chen et al. 2023).

Neolepetopsidae stet.

Fig. 31G, H

Reference. Several morphospecies were reported in Electronic supplemental table S6 of Levin et al. (2012) (occurrences only, Jacó Scar).

Material examined. AD4501: M11963; AD4502: M12093; AD4586: M18777, M18780, M18800, M18802, M18804, M18807; AD4587: M19015, M19116, M19155, M19156; AD4588: M19019, M19020, M19025, M19031, M19034, M19035, M19040, M19041, M19060, M19065, M19071, M19097, M19108, M19138, M19046, M19050, M19053, M19064, M19070, M19084, M19154; AD4589: M18813, M18827, M18839, M18842, M18848, M18858, M18864, M18910, M18918, M18926, M18929, M18958, M18964, M18966, M19139, M19140, M19141, M19157; AD4590: M18990; AD4591: M18874, M18882, M18885, M18892, M18902, M18903, M19163.

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Remarks. Under genetic and morphological investigation (Betters et al. (2024), in press at the time of this work’s acceptance). Neolepetopsidae and Paralepetopsis appear to be paraphyletic (Chen et al. 2023).

Paralepetopsis cf. clementensis J. H. McLean, 2008

Fig. 32A

Figure 32. 

Mollusca: Gastropoda: Patellogastropoda and Caenogastropoda, representative images. Live specimens are depicted unless otherwise specified A Paralepetopsis cf. clementensis (M18937, preserved specimen in dorsal, ventral, and lateral view) B Bathyacmaea stet. (M11987, same specimen in dorsal and lateral view) C Fuscapex stet. (M12006) D Alvania stet. (M18834, same preserved specimen in lateral and apertural view) E Vitrinellidae stet. (M19091, same preserved specimen in apical and umbilical view) F Neptunea stet. (M12023) G Cancellaria nr. rosewateri (M12051, apertural view) H Cancellaria nr. rosewateri (M12051, lateral view). Scale bars: 1 mm (A–F); 1 cm (G, H).

Reference. Reported in Electronic supplemental table S6 of Levin et al. (2012) as “Neolepetopsis [sic] clementensis” (occurrences only).

Material examined. AD4590: M18930, M18935, M18937, M18961, M18969, M18976, M18980, M18989, M19142; AD4591: M18884, M18901.

Localities. Jacó Scar (~ 1800 m).

Distribution. Paralepetopsis clementensis is known only from a whale fall off southern California at 1800 m depth (McLean 2008). Genetic confirmation of the CRM seep occurrences would represent new southern records and the first seep records for this species. Additional specimens of Paralepetopsis are under morphological and genetic investigation (Betters et al. (2024), in press at the time of this work’s acceptance).

Mollusca | Gastropoda | Patellogastropoda | Lottioidea | Pectinodontidae

Bathyacmaea stet.

Fig. 32B

Reference. Electronic supplemental table S6 of Levin et al. (2012) (occurrences only, Jacó Scar).

Material examined. AD4503: M11987; AD4587: M18812; AD4590: M18925, M18928, M18945, M18953, M18960, M18968, M18978, M18987; AD4591: M18873, M18881, M18888, M18893, M19151.

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Remarks. Under genetic and morphological investigation (Betters et al. (2024), in press at the time of this work’s acceptance).

Mollusca | Gastropoda | Caenogastropoda | Littorinimorpha | Eulimidae

Fuscapex stet.

Fig. 32C

Material examined. AD4506: M12006.

Localities. Parrita Seep (~ 1030–1033 m).

Remarks. The host of this specimen was not determined, but Fuscapex is only known as a parasite on ophiuroids (Bouchet and Warén 1986). The specimen was recovered among various animals associated with a coralliid (voucher specimen Co2271), including potential hosts Ophiacantha moniliformis (voucher specimen E4390) and Ophiuroglypha cf. meridionalis (voucher specimen E7978).

Mollusca | Gastropoda | Caenogastropoda | Littorinimorpha | Rissoidae

Alvania stet.

Fig. 32D

Material examined. AD4589: M18834.

Localities. Mound 12 (997 m).

Remarks. Associated with a naturally occurring wood fall.

Mollusca | Gastropoda | Caenogastropoda | Littorinimorpha | Vitrinellidae

Vitrinellidae stet.

Fig. 32E

Material examined. AD4587: M19091.

Localities. Mound 12 (996 m).

Remarks. Associated with a naturally occurring wood fall.

Mollusca | Gastropoda | Caenogastropoda | Neogastropoda | Buccinidae

Neptunea amianta (Dall, 1890) sp. inc.

Fig. 32F

Material examined. AD4508: M12023; AD4913: M16143; S0230: M17099.

Localities. Parrita Seep (~ 1401–1419 m), Jacó Scar (1847 m), Mound Jaguar (1908 m).

Remarks. Possibly a southern range extension of Neptunea amianta, which was originally described from southern California at 757 m and has been reported from the Bering Sea off Alaska to northern Baja California, 100–3500 m (McLean 1996). Scavenging aggregations of N. amianta have been associated with organic falls and seeps (McClain and Nekola 2007).

Mollusca | Gastropoda | Caenogastropoda | Neogastropoda | Cancellariidae

Cancellaria nr. rosewateri Petit, 1983

Fig. 32G, H

Material examined. AD4510: M12051.

Localities. Jacó Summit (744 m).

Remarks. This specimen warrants further comparison to Cancellaria rosewateri, described from the Gulf of Mexico, 366 m (Petit 1983).

Mollusca | Gastropoda | Caenogastropoda | Neogastropoda | Raphitomidae

Gymnobela stet.

Fig. 33A

Figure 33. 

Mollusca: Gastropoda: Caenogastropoda, representative images. Live specimens are depicted unless otherwise specified A Gymnobela stet. (M17041, three specimens) B Phymorhynchus gen. inc. (M17038, apertural view) C Phymorhynchus gen. inc. (M17038, lateral view) D Abyssochrysos stet. (M18994, same preserved specimen in lateral and apertural view) E Provanna ios (M16807, apertural views) F Provanna ios (M16807, apico-lateral views) G Provanna laevis (M16104) H Provanna laevis (M17030, with bacteria). Scale bars: 1 cm (A–C); 1 mm (D–H).

Material examined. AD4504: M11990 (PQ449396); AD4988: M16958; S0217: M17041.

Localities. Mound 11 (~ 999–1025 m), The Thumb (1069 m).

Remarks. For M11990, the closest COI BLASTN result on GenBank was a specimen of Typhlosyrinx (Raphitomidae) from Papua New Guinea, 680–689 m (MH308407.1, 93.26% identity) (Uribe et al. 2018).

Phymorhynchus gen. inc.

Fig. 33B, C

Material examined. S0214: M17038.

Localities. Jacó Scar (1801 m).

Mollusca | Gastropoda | Caenogastropoda | Abyssochrysoidea | Abyssochrysidae

Abyssochrysos stet.

Fig. 33D

Material examined. AD4587: M18994.

Localities. Mound 12 (~ 9900–996 m).

Mollusca | Gastropoda | Caenogastropoda | Abyssochrysoidea | Provannidae

Provanna ios Warén & Bouchet, 1986

Fig. 33E, F

Reference. Betters and Cordes 2024.

Localities. Jacó Scar (~ 1800–2000 m) and an unnamed locality (8.5958, -84.4370) at 1917 m depth, ca 12 km northwest of Parrita Seep.

Distribution. Eastern Pacific vents, 21°N to 17°S (type locality: 13°N on the East Pacific Rise) (Warén and Bouchet 1986), and the CRM seeps, 1757–2620 m depth (Sasaki et al. 2010; Betters and Cordes 2024).

Provanna laevis Warén & Ponder, 1991

Fig. 33G, H

References. Betters and Cordes 2024.

Localities. Jacó Summit (~ 740–760 m), Mound 12 (~ 900–1050 m), The Thumb (~ 1071–1075 m).

Distribution. Originally described from the Guaymas Basin, Gulf of California, 2004 m (Warén and Ponder 1991), and reported at eastern Pacific vents and seeps from the Juan de Fuca Ridge to the CRM, 500–2004 m depth (Warén and Bouchet 2001; Betters and Cordes 2024). A recent synonymization of Provanna glabra Okutani, Tsuchida & Fujikura, 1992, extends the range of P. laevis to western Pacific seeps from Iheya Ridge to Sagami Bay (Betters and Cordes 2024).

Remarks. Some CRM specimens were associated with naturally occurring or experimentally deployed wood (Betters et al. 2023; Betters and Cordes 2024). Consistent with previous reports from the Oregon Margin (Warén and Bouchet 2001), Pyropelta cf. corymba was often attached to the shells. Some P. laevis shells were coated with elongated pustules (Fig. 33H) resembling the Thiomargarita-like sulfur-oxidizing bacteria reported on other gastropods from the CRM seeps (Bailey et al. 2011). Similar pustules have been observed on the shells of vent gastropods such as Depressigyra spp. (Warén and Bouchet 1989; Desbruyères et al. 2006) and Lepetodrilus gordensis S. B. Johnson, C. R. Young, W. J. Jones, Warén & Vrijenhoek, 2006 (Johnson et al. 2006).

Provanna pacifica (Dall, 1908)

Fig. 34A, B

Figure 34. 

Mollusca: Gastropoda: Caenogastropoda and Heterobranchia, representative live images A Provanna pacifica (M16955, apertural views) B Provanna pacifica (M16955, lateral views) C Aeolidioidea stet. (M16811) D Fionoidea stet. (M11992) E Goniodorididae sp. SIO_BIC_M16185 (M16185, dorsal view) F Goniodorididae sp. SIO_BIC_M16185 (M16185, lateral view) G Eulimella lomana (in situ), Dive S0214 at Jacó Scar, 1781 m. Credit: ROV SuBastian/Schmidt Ocean Institute H Pyramidellidae stet. (M16901). Scale bars: 1 mm.

Reference. Betters and Cordes 2024.

Localities. Mound 11 (~ 1000–1100 m), Parrita Seep (~ 1300–1500 m).

Distribution. Associated with naturally occurring sunken wood and seeps, Oregon Margin to the Gulf of Panama (type locality), 1000–2750 m (Warén and Bouchet 1986; Betters and Cordes 2024).

Mollusca | Gastropoda | Heterobranchia | Euthyneura | Ringipleura | Nudibranchia | Cladobranchia

Aeolidioidea stet.

Fig. 34C

Material examined. AD4975: M16811; AD4985: M16907.

Localities. Mound 12 (997–1002 m).

Fionoidea stet.

Fig. 34D

Material examined. AD4504: M11992; AD4906: M16094.

Localities. Mound 11 (~ 1004–1011 m), Mound 12 (~ 997–1002 m).

Remarks. M11992 was associated with naturally occurring sunken plant material.

Mollusca | Gastropoda | Heterobranchia | Euthyneura | Ringipleura | Nudibranchia | Doridina

Goniodorididae sp. SIO_BIC_M16185

Fig. 34E, F

Material examined. AD4918: M16185 (PQ449415).

Localities. Quepos Slide (394 m).

Remarks. The closest COI BLASTN results on GenBank were within Goniodorididae, e.g., Ceratodoris pilosa (Bouchet & Ortea, 1983) from Japan (MW357567.1, 88.94% identity), Okenia mediterranea (Ihering, 1886) from Italy (MK645760.1, 88.78% identity), and O. amoenula (Bergh, 1907) from South Africa (KF192606.1, 88.63% identity).

Mollusca | Gastropoda | Heterobranchia | Euthyneura | Tectipleura | Pyramidellidae

Eulimella lomana (Dall, 1908)

Fig. 34G

Reference. Electronic supplemental table S6 of Levin et al. (2012) (occurrences only, Jacó Scar).

Material examined. AD4590: M18971.

Localities. Jacó Scar (~ 1800 m).

Distribution. Known from seeps, vents (likely sedimented vents), and whale falls, 1168–2008 m, from southern California (type locality) and the Guaymas Basin, Gulf of California (Warén and Bouchet 1993; Sasaki et al. 2010; Portail et al. 2015).

New records. The CRM specimen represents a new southern record for this species.

Remarks. Pyramidellids are thought to be exclusively parasitic, typically on mollusks or polychaetes, but a definitive host has not been identified for E. lomana (Warén and Bouchet 1993). Specimen M18971 could not be linked to a potential host. Another specimen at Jacó Scar (not collected) was observed on vesicomyid clams (Fig. 34G).

Pyramidellidae stet.

Fig. 34H

Material examined. AD4508: M12029; AD4912: M16125; AD4987: M16901; AD4989: M16942.

Localities. Mound 12 (1010 m), Parrita Seep (~ 1401–1419 m), Jacó Scar (1842 m).

Remarks. At least one additional morphospecies is present and distinct from E. lomana.

Mollusca | Gastropoda | Heterobranchia | Mesoneura | Tjaernoeioidea | Aplustridae

Parvaplustrum stet.

Fig. 35A, B

Figure 35. 

Mollusca: Gastropoda: Heterobranchia, representative images. Live specimens are depicted unless otherwise specified A Parvaplustrum stet. (M17071, apertural view; scale not recorded for specimens destroyed in DNA extraction; estimated shell length 1-2 mm) B Parvaplustrum stet. (M17071, lateral view) C Architectonicidae fam. inc. (M19335, same preserved specimen in apical and umbilical view) D Lurifax gen. inc. (M19337, same preserved specimen in apical and umbilical view) E Orbitestella gen. inc. (M19136, same preserved specimen in apical and umbilical view) F Hyalogyra stet. (M18944, same preserved specimen in apical and umbilical view) G Hyalogyrina sp. SIO_BIC_M16774 (M16774, lateral view) H Hyalogyrina sp. SIO_BIC_M16774 (M16774, ventral view). Scale bars: 1 mm.

Material examined. S0219: M17071.

Localities. Rio Bongo Scar (609 m).

Remarks. Collected from a microbial mat. DNA sequences could not be obtained.

Mollusca | Gastropoda | Heterobranchia | “Lower Heterobranchia” | Architectonicoidea | Architectonicidae

Architectonicidae fam. inc.

Fig. 35C

Material examined. AD4505: M19335.

Localities. Mound 11 (1025 m).

Remarks. Identification is uncertain due to the corroded condition of the shell.

Mollusca | Gastropoda | Heterobranchia | “Lower Heterobranchia” | Orbitestelloidea | Orbitestellidae

Lurifax gen. inc.

Fig. 35D

Material examined. AD4504: M19337; AD4505: M19336.

Localities. Mound 11 (1009–1025 m).

Remarks. Identification is uncertain.

Orbitestella gen. inc.

Fig. 35E

Material examined. AD4589: M19136.

Localities. Mound 12 (997 m).

Remarks. Identification is uncertain due to the corroded condition of the shell.

Mollusca | Gastropoda | Heterobranchia | “Lower Heterobranchia” | Valvatoidea | Hyalogyrinidae

Hyalogyra stet.

Fig. 35F

Material examined. AD4586: M18799; AD4587: M19010, M19087; AD4588: M19026, M19043, M19074, M19088, M19135; AD4589: M18837, M19137; AD4590: M18907, M18919, M18920, M18942, M18944, M19145, M19338.

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Remarks. Two morphospecies were distinguished as “tall” and “planispiral”.

Hyalogyrina stet.

Fig. 35G, H

Reference. Electronic supplemental table S6 of Levin et al. (2012) (occurrences only, Jacó Scar).

Material examined. AD4510: M12043; AD4587: M13003, M13004, M18991, M18992, M19000, M19001, M19007, M19144, M19147; AD4590: M18323, M18981, M19330; AD4914: M16151 (PQ449414); AD4974: M16774; S0213: M17029 (PQ449419).

Localities. Jacó Summit (741–742 m), Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Remarks. Most specimens were collected from microbial mat habitats. At least two morphospecies were distinguished (Levin et al. 2012). One morphospecies, represented by M17029, has a pale shell with a broad yellow blaze on the outer whorl. The CRM specimens warrant comparison to Hyalogyrina grasslei Warén & Bouchet, 1993, which is known from hydrothermal vents and seeps at ~ 2000 m in the Guaymas Basin, Gulf of California (Warén and Bouchet 1993; Sasaki et al. 2010).

Mollusca | Gastropoda | Vetigastropoda | Lepetellida | Lepetelloidea | Caymanabyssiidae

Colotrachelus stet.

Fig. 36A

Figure 36. 

Mollusca: Gastropoda: Vetigastropoda, representative images. Live specimens are depicted unless otherwise specified A Colotrachelus stet. (M19101, separate preserved specimens in dorsal and ventral view) B Pyropelta cf. corymba (M16105) C Pyropelta cf. musaica (M19044, same preserved specimen in dorsal and ventral view) D Pyropelta cf. wakefieldi (M11966, separate specimens in dorsal and ventral view) E Pyropelta cf. wakefieldi (M11966, lateral view) F Lepetodrilus aff. shannonae (M11973, separate specimens in dorsal and ventral view) G Lepetodrilus guaymasensis (M16142, separate specimens in lateral and dorsal view) H Lepetodrilus guaymasensis (M16142, ventral view). Scale bars: 1 mm.

Material examined. AD4587: M19093, M19101, M19120, M19129.

Localities. Mound 12 (~ 1000 m).

Mollusca | Gastropoda | Vetigastropoda | Lepetellida | Lepetelloidea | Pyropeltidae

Pyropelta cf. corymba McLean & Haszprunar, 1987

Fig. 36B

Reference. Reported in Electronic supplemental table S6 of Levin et al. (2012) as Pyropelta corymba (occurrences only, Jacó Scar).

Material examined. AD4501: M11968; AD4586: M18801; AD4587: M19096, M19343; AD4588: M19033, M19049, M19059, M19073, M19160, M19347; AD4589: M18322, M18830, M18841, M18851, M18863, M19078; AD4590: M18908; AD4910: M16105, M16107; AD4917: M16157; AD4978: M16874.

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Remarks. Pyropelta corymba was originally described from hydrothermal vents in the Guaymas Basin, Gulf of California, 2022 m (McLean and Haszprunar 1987), and subsequently reported from seeps on the Oregon Margin, 524 m (Warén and Bouchet 2001), as well as from whale falls off southern California, 940–1240 m (McLean 1992). If confirmed as P. corymba by genetic comparison to material from the type locality, the CRM seep specimens would represent new southern records for this species. Consistent with previous reports (Warén and Bouchet 2001; Desbruyères et al. 2006), many CRM specimens were associated with Provanna laevis.

Pyropelta cf. musaica McLean & Haszprunar, 1987

Fig. 36C

Material examined. AD4586: M17850, M18781, M18811, M19348; AD4587: M19008, M19090, M19109, M19113, M19122; AD4588: M19022, M19023, M19032, M19044, M19054, M19066, M19085, M19162, M19346; AD4589: M18831, M18843, M18850, M19077; AD4590: M18940, M18988; AD4591: M18324, M18883, M18900.

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Remarks. Pyropelta musaica was originally described from hydrothermal vents at the Axial Seamount, Juan de Fuca Ridge, 1575 m (McLean and Haszprunar 1987). It has been reported from the Jalisco Block seeps, Mexico, at 3000–3775 m (Warén and Bouchet 2001; Desbruyères et al. 2006), and from whale falls across California at 940–1400 m (McLean 1992). If confirmed as P. musaica by genetic comparison to material from the type locality, the CRM seep occurrences would represent new southern records for this species.

Pyropelta cf. wakefieldi McLean, 1992

Fig. 36D, E

Material examined. AD4501: M11966 (PQ450396); AD4586: M17849, M18797, M18803, M18808, M18810; AD4587: M19011, M19016, M19112; AD4588: M19021, M19030, M19048, M19072, M19075, M19134, M19148, M19150, M19340, M19341, M19342, M19344; AD4589: M18829, M18835, M18849, M18857, M18862, M19076; AD4590: M18956, M18959.

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Remarks. Pyropelta wakefieldi was originally described from a whale fall off Point Sur, California, 940 m (McLean 1992). Genetic confirmation of the CRM seep occurrences would represent new southern records and new seep records for this species. The closest COI BLASTN result on GenBank was Pyropelta sp. SWA-2009 from the Gulf of Mexico (FJ977753.1, 90.99% identity).

Mollusca | Gastropoda | Vetigastropoda | Lepetellida | Lepetodriloidea | Lepetodrilidae

Lepetodrilus aff. shannonae Warén & Bouchet, 2009

Fig. 36F

Reference. Electronic supplemental table S6 of Levin et al. (2012) (occurrences only, Jacó Scar).

Material examined. AD4501: M11973; AD4511: M12057; AD4590: M18904, M18943, M18985, M19152; AD4591: M18875, M18879, M18891, M18898.

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Remarks. The CRM specimens appear morphologically similar to L. shannonae, known only from hydrocarbon seeps off the Congo River, West Africa, 2300–3150 m (Warén and Bouchet 2009).

Lepetodrilus guaymasensis McLean, 1988

Fig. 36G, H

References: Johnson et al. 2008; Matabos and Jollivet 2019; Electronic supplemental table S6 of Levin et al. (2012) (occurrences only, Jacó Scar).

Additional material examined. AD4508: M12020 (PQ450397); AD4586: M18778, M18809; AD4587: M19107, M19111, M19118; AD4588: M19018, M19028, M19058, M19069; AD4589: M18817, M18828, M18836, M18845, M18856, M18860; AD4590: M18911, M18914, M18922, M18927, M18938, M18947, M18950, M18967, M18970, M18979, M18983, M19349 to M19382; AD4591: M18872, M18878, M18890, M18897; AD4912: M16142; AD4917: M16159.

Localities. Mound 12 (~ 1000 m; this study), Parrita Seep (~ 1400 m; this study), Jacó Scar (~ 1800 m), “Mudpie” seep ~ 10 km west of Parrita Scar (8.983, -84.717; 1917 m) (Johnson et al. 2008).

Distribution. Originally described from sedimented hydrothermal vents and seeps in the Guaymas Basin, Gulf of California, 2000–2019 m, often in association with Riftia pachyptila Jones, 1981 (McLean 1988, 1993; Sasaki et al. 2010). Specimens from the CRM “Mudpie” seep were confirmed as L. guaymasensis based on COI comparison to specimens from the type locality (Matabos and Jollivet 2019).

Remarks. The COI sequence of M12020 was 100.00% identical to that of L. guaymasensis from the CRM Mudpie site (EU306419.1, voucher SMNH 82443, Swedish Museum of Natural History).

Lepetodrilus stet.

Fig. 37A

Figure 37. 

Mollusca: Gastropoda: Vetigastropoda, representative live images A Lepetodrilus stet (M11965, same specimen in dorsal and ventral view) B Anatoma stet. (M16187, same specimen in apical, lateral, and umbilical view) C Bathyxylophila stet. (M12038, separate specimens in apical and umbilical view) D Bathyxylophila stet. (M16199) E Kanoia myronfeinbergi (M16771) F Kanoia cf. myronfeinbergi (M12053) G Haplotype network of Kanoia COI sequences. Scale bars: 1 mm (A–D); 1 cm (E, F).

Material examined. AD4501: M11965.

Localities. Mound 12 (~ 984–997 m).

Remarks. Additional Lepetodrilus morphospecies may occur at the CRM. For example, an undescribed Lepetodrilus “sp. CR” has been reported from a CRM seep site at 1900 m, but it is represented by a single specimen without available DNA sequences (Johnson et al. 2008). Specimen M11965 and others resemble L. elevatus J. H. McLean, 1988, which was originally described as two subspecies from the East Pacific Rise and the Galápagos Rift (McLean 1988). The L. elevatus species complex comprises four genetically distinct lineages (Johnson et al. 2008; Matabos and Jollivet 2019). Additional specimens of Lepetodrilidae from the CRM are under genetic and morphological investigation (Betters et al. (2024), in press at the time of this work’s acceptance).

Mollusca | Gastropoda | Vetigastropoda | Lepetellida | Scissurelloidea | Anatomidae

Anatoma stet.

Fig. 37B

Reference. Electronic supplemental table S6 of Levin et al. (2012) (occurrences only, Jacó Scar).

Material examined. AD4591: M18899; AD4918: M16187.

Localities. Quepos Slide (~ 333–408 m), Jacó Scar (1753 m).

Mollusca | Gastropoda | Vetigastropoda | Lepetellida | Scissurelloidea | Larocheidae

Bathyxylophila stet.

Fig. 37C, D

Material examined. AD4508: M12028; AD4509: M12038, M12039, M18869; AD4587: M18317, M19092, M19099, M19128; AD4923: M16198, M16199; AD4976: M16797, M16798, M16801; AD4988: M16954, M16965.

Localities. Mound 12 (~ 1000 m), Mound 11 (1010 m), Parrita Seep (~ 1000–1400 m), Jacó Scar (~ 1800 m).

Remarks. Associated with naturally occurring or experimentally deployed wood falls. Likely at least two morphospecies are represented. Some of the specimens of M16199 (Fig. 37D) require further verification.

Mollusca | Gastropoda | Vetigastropoda | Seguenziida | Seguenzioidea | Cataegidae

Kanoia myronfeinbergi Warén & Rouse, 2016

Fig. 37E

References. Warén and Rouse 2016**. Prior to description, this morphospecies was reported at Jacó Scar as “Cataegis sp.” in Electronic supplemental table S6 of Levin et al. (2012).

New sequences. We provide COI sequences for the following specimens cited in Warén and Rouse (2016), in some cases under catalog numbers from the Swedish Museum of Natural History, SMNH: AD4501: M11976 (PQ449395); AD4587: M14422 (PQ449410; ex SMNH 108692), M14424 (PQ449411; ex SMNH 109248); AD4588: M18331 (PQ449427; ex SMNH 108742); AD4589: M14418 (PQ449405; tissue from voucher SMNH 108441); AD4590: M14421 (PQ449409; tissue from voucher SMNH 108604); AD4591: M14419 (PQ449406; ex SMNH 108504), M14420A (PQ449407; ex SMNH 108525), M14420B (PQ449408; ex SMNH 108525); Guaymas Basin seeps: M13149 (PQ432664), M13150 (PQ432665), M13151 (PQ432666); Del Mar seeps: M14395 (PQ432667).

Localities. Mound 12 (~ 1000 m; type locality), Jacó Scar (~ 1800 m); additional seep sites off Costa Rica and Nicaragua (1002–1917 m) (Warén and Rouse 2016).

Distribution. Also known from seeps in the Guaymas Basin at ~ 1570 m and seeps off Del Mar, California, ~ 1020 m (Warén and Rouse 2016).

Kanoia cf. myronfeinbergi Warén & Rouse, 2016

Fig. 37F

Reference. Warén and Rouse 2016.

New sequences. AD4510: M12053 (PQ449403); AD4587: M18315 (PQ449426; tissue from voucher SMNH 108680). In Warén and Rouse (2016), specimen M12053 was morphologically identified as K. myronfeinbergi whereas M18315 was not identified to species due to corrosion of the shell.

Localities. Jacó Summit (~ 741–744 m), Mound 12 (~ 990–996 m).

Remarks. The description of K. myronfeinbergi notes the possibility of a second, cryptic species “with less distinct sculpture, more similar to Kanoia meroglypta from the Caribbean,” although detailed assessment of shell sculpture is difficult due to the corrosion on many specimens (Warén and Rouse 2016).

To investigate the genetic basis for this variation, we constructed a COI haplotype network using a subset of the specimens examined in the original description (Fig. 37G). Two COI sequences showed a minimum uncorrected distance of 4.3% (over 539 bp) from the others. Although there is no universally applicable threshold for species delimitation, numerous deep-sea gastropod species are separated by a minimum of 4–7% COI divergence (Johnson et al. 2008; Chen et al. 2019a). We conservatively designate the two high-divergence specimens as K. cf. myronfeinbergi, and we note the co-occurrence of this haplotype with others at Mound 12. The other K. myronfeinbergi sequences showed minimal variation across localities from Costa Rica to California (maximum uncorrected distance 1.11%). Further clarification on Kanoia species delimitation will require genetic and morphological analysis of more individuals from various localities and depths, especially those < 1000 m to explore potential depth segregation.

Mollusca | Gastropoda | Vetigastropoda | Seguenziida

Xyloskenea stet.

Fig. 38A

Figure 38. 

Mollusca: Gastropoda: Vetigastropoda and Neomphaliones, representative images. Live specimens are depicted unless otherwise specified A Xyloskenea stet. (M19013, two preserved specimens) B Escondidacantrainea panamensis (M17848, apical view) C Escondidacantrainea panamensis (M17848, umbilical view) D Dillwynella stet (M17884) E Fucaria stet. (M12068, two specimens) F Bathysciadium stet. (M19002, same preserved specimen in dorsal and lateral view) G Cocculina stet. (M19166, same preserved specimen in dorsal and ventral view) H Cocculinidae fam. inc. (M16727, same specimen in dorsal and ventral view). Scale bars: 1 mm (A, D–H); 1 cm (B, C).

Material examined. AD4509: M18870, M19159; AD4587: M19013, M19334; AD4923: M16197.

Localities. Mound 12 (~ 1000 m), Parrita Seep (~ 1100 m), Jacó Scar (~ 1800 m).

Remarks. M16197 and M18870 were associated with naturally occurring wood falls.

Mollusca | Gastropoda | Vetigastropoda | Trochida | Trochoidea | Colloniidae

Escondidacantrainea panamensis (Dall, 1908)

Fig. 38B, C

Material examined. AD4587: M17848, M19103.

Localities. Mound 12 (995–996 m).

Distribution. Originally described from the Gulf of Panama, 1015 m (Dall 1908), and recorded south to the Concepción seeps off central Chile, 740–870 m (Sasaki et al. 2010).

Remarks. M17848 and M19103 were associated with naturally occurring wood falls.

Mollusca | Gastropoda | Vetigastropoda | Trochida | Trochoidea | Skeneidae

Dillwynella stet.

Fig. 38D

Reference. Reported in Electronic supplemental table S6 of Levin et al. (2012) as “Dillwynella panamensis” (occurrences only, Jacó Scar).

Material examined. AD4586: M18805; AD4587: M18320, M19095, M19098, M19117, M19124, M19158; AD4588: M17884, M19052; AD4589: M18832; AD4590: M18957.

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Remarks. Many specimens were associated with wood falls, either experimentally deployed (M17884, M18805, M19052) or naturally occurring (M18320, M19095, M19098, M19117, M19124, M19158). These specimens warrant comparison to Ganesa panamensis Dall, 1902, which is known only from the Gulf of Panama, 1865 m, and has been regarded as possibly belonging to the genus Dillwynella (Dall 1902; Kunze 2011).

Fucaria stet.

Fig. 38E

Reference. Electronic supplemental table S6 of Levin et al. (2012) (occurrences only, Jacó Scar).

Material examined. AD4513: M12068; AD4591: M18880, M18887; AD4590: M18906, M18923, M18941, M18946, M18951, M18986, M19165; AD4591: M18896.

Localities. Jacó Scar (~ 1800 m).

Mollusca | Gastropoda | Neomphaliones

We follow the subdivisions of Neomphaliones based on the mitogenome phylogeny in Zhong et al. (2022).

Mollusca | Gastropoda | Neomphaliones | Cocculinida | Bathysciadiidae

Bathysciadium stet.

Fig. 38F

Material examined. AD4587: M19002.

Localities. Mound 12 (~ 990–996 m).

Mollusca | Gastropoda | Neomphaliones | Cocculinida | Cocculinidae

Cocculina stet.

Fig. 38G

Material examined. AD4503: M19166; AD4588: M18321, M19089.

Localities. Mound 12 (~ 1000 m).

Cocculinidae fam. inc.

Figs 38H, 39A, B

Figure 39. 

Mollusca: Gastropoda: Neomphaliones, representative images. Live specimens are depicted unless otherwise specified A Cocculinidae fam. inc. (M16816, dorsal view) B Cocculinidae fam. inc. (M16816, ventral view) C Leptogyropsis gen. inc. (M19102, same preserved specimen in apical, umbilical, and apertural view) D Helicrenion stet. (M18909, two preserved specimens) E Neomphalidae sp. SIO_BIC_M14645 (M14645, two specimens) F Neomphalidae sp. SIO_BIC_M14645 (M14645, ventral view) G Peltospiridae stet. (M16802, dorsal view) H Peltospiridae stet. (M16802, ventral view). Scale bars: 1 mm.

Material examined. AD4972: M16726, M16727, M16728; AD4974: M16789, M16790; AD4976: M16816, M16817.

Localities. Mound 12 (~ 1000 m), Jacó Scar (~ 1800 m).

Remarks. Associated with experimentally deployed wood. Under morphological and genetic investigation (Betters et al. (2024), in press at the time of this work’s acceptance).

Mollusca | Gastropoda | Neomphaliones | Neomphalida | Melanodrymiidae

Leptogyropsis gen. inc.

Fig. 39C

Material examined. AD4587: M19102, M19146.

Localities. Mound 12 (996 m).

Remarks. Associated with a naturally occurring wood fall.

Mollusca | Gastropoda | Neomphaliones | Neomphalida | Neomphalidae

Helicrenion stet.

Fig. 39D

Material examined. AD4508: M12027; AD4586: M18782; AD4587: M18993, M18999, M19004; AD4589: M18818; AD4590: M18909; AD4988: M16962.

Localities. Mound 11 (1009 m), Mound 12 (~ 1000 m), Parrita Seep (~ 1400 m), Jacó Scar (~ 1800 m).

Remarks. Possibly an undescribed species. Several specimens (M16962, M18993, M18999, and M19004) were collected from microbial mat habitats.

Neomphalidae sp. SIO_BIC_M14645

Fig. 39E, F

Material examined. AD4910: M14645; AD4917: M14646 (PQ449412).

Localities. Mound 12 (~ 1000 m).

Remarks. An undescribed genus and species.

Mollusca | Gastropoda | Neomphaliones | Neomphalida | Peltospiridae

Peltospiridae stet.

Fig. 39G, H

Material examined. AD4976: M16802.

Localities. Jacó Scar (1887 m).

Remarks. Associated with experimentally deployed wood.

Mollusca | Scaphopoda

Gadilida stet.

Fig. 40A

Figure 40. 

Mollusca: Scaphopoda, Cephalopoda, and Aplacophora: Caudofoveata, representative live and SEM images A Siphonodentalium gen. inc. (M12048) B Gadilida stet. (M12049) C Octopodoidea stet. (M17037, dorsal view) D Octopodoidea stet. (M17037, detail) E Planctoteuthis danae (M17039) F Chaetoderma stet. (M16155, incomplete specimen, cuticle missing from part of the body) G Chaetodermatidae sp. SIO_BIC_M12018 (M12018) H Chaetodermatidae sp. SIO_BIC_M12018 (M12019, SEM). Scale bars: 1 mm (A, B, G); 1 cm (C, E, F); 0.3 mm (H).

Material examined. AD4510: M12049.

Localities. Jacó Summit (744 m).

Siphonodentalium gen. inc.

Fig. 40B

Material examined. AD4510: M12048; AD4511: M12056.

Localities. Jacó Summit (742 m), Mound 12 (~ 988–997 m).

Mollusca | Cephalopoda

We thank Michael Vecchione (National Marine Fisheries Service National Systematics Laboratory, U.S. National Museum of Natural History) for assistance with these identifications.

Mollusca | Cephalopoda | Octopoda

Octopodoidea sp. SIO_BIC_ M17037

Fig. 40C, D

Material examined. S0216: M17037.

Localities. Quepos Slide (317 m) .

Remarks. Likely an undescribed species, possibly an undescribed genus. The animal was observed releasing ink (potentially a diagnostic character).

Mollusca | Cephalopoda | Oegopsida

Planctoteuthis danae (Joubin, 1931)

Fig. 40E

Material examined. S0215: M17039.

Localities. Mound 12 (1016 m depth, 2–3 m above the seafloor).

Distribution. Originally described from the Gulf of Panama and considered cosmopolitan in tropical and temperate waters worldwide (Jereb and Roper 2010).

Mollusca | Caudofoveata

We use the clade-based high-level taxonomic names in Kocot et al. (2019).

Chaetoderma stet.

Fig. 40F

Material examined. AD4917: M16155; AD4977: M16809.

Localities. Jacó Scar (1783–1791 m).

Chaetodermatidae sp. SIO_BIC_M12018

Fig. 40G, H

Material examined. AD4508: M12018 (PQ449402), M12019; AD4972: BI1338 (PQ449340).

Localities. Parrita Seep (~ 1401–1419 m), Jacó Scar (1746 m).

Remarks. The closest COI BLASTN result on GenBank was the holotype of Chaetoderma felderi Ivanov & Scheltema, 2007 (AM922259.1; 93.33% identity to M12018, 93.18% identity to BI1338). Based on COI, these specimens belong within Chaetodermatidae and may belong to Chaetoderma or Falcidens, but these genera are not reciprocally monophyletic (Mikkelsen et al. 2019).

Chaetodermatidae sp. SIO_BIC_M16812

Material examined. AD4975: M16812 (PQ449416; no image available).

Localities. Mound 12 (1000 m).

Remarks. The closest COI BLASTN result on GenBank was the holotype of Chaetoderma felderi (AM922259.1; 90.21% identity). As above, this specimen may belong to Chaetoderma or Falcidens.

Chaetodermatidae sp. SIO_BIC_M16891

Fig. 41A

Figure 41. 

Mollusca: Aplacophora: Caudofoveata and Solenogastres, representative live and SEM images A Chaetodermatidae sp. SIO_BIC_M16891 (M16891, SEM) B Neomenia gen. inc. (M18409) C Gymnomeniidae stet. (M16924) D Gymnomeniidae stet. (M16924, SEM) E Wirenia sp. SIO_BIC_M17072 (M17072) F Wirenia sp. SIO_BIC_M17072 (M17072, SEM) G Pholidoskepia stet. (M16923) H Pholidoskepia stet. (M16923, SEM). Scale bars: 0.3 mm (A); 1 mm (B, C, E, G); 0.02 mm (D, F, H).

Material examined. AD4979: M16891 (PQ435556).

Localities. Quepos Slide (397 m).

Remarks. The closest COI BLASTN result on GenBank was an undescribed species of Falcidens (MG855756.1; 93.93% identity). As above, this specimen may belong to Chaetoderma or Falcidens.

Mollusca | Solenogastres

We use the clade-based high-level taxonomic names in Kocot et al. (2019). Groups that have been historically assigned to the non-monophyletic “Cavibelonia” are listed last.

Mollusca | Solenogastres | Neomeniamorpha | Neomeniidae

Neomenia gen. inc.

Fig. 41B

Material examined. S0219: M18409.

Localities. Rio Bongo Scar (606 m).

Mollusca | Solenogastres | Pholidoskepia | Gymnomeniidae

Gymnomeniidae stet.

Fig. 41C, D

Material examined. AD4990: M16924 (PQ435558; 16S: PQ304664).

Localities. Parrita Seep (1401 m).

Wirenia sp. SIO_BIC_M17072

Fig. 41E, F

Material examined. S0219: M17072 (PQ435553; 16S: PQ304665).

Localities. Rio Bongo Scar (606 m).

Remarks. This undescribed species has keeled, leaf-like sclerites typical of Wirenia, but it is easily distinguished from all described species by the extremely small size (< 200 µm) of the sclerites.

Mollusca | Solenogastres | Pholidoskepia

Pholidoskepia stet.

Fig. 41G, H

Material examined. AD4990: M16923 (PQ435557; 16S: PQ304663).

Localities. Parrita Seep (1401 m).

Remarks. Genetic data place this specimen within Pholidoskepia sensu Kocot et al. 2019. It is possibly a member of Sandalomeniidae, pending further molecular characterization of this group.

Mollusca | Solenogastres | Amphimeniidae

Amphimeniidae stet.

Fig. 42A

Figure 42. 

Mollusca: Aplacophora: Solenogastres and Polyplacophora, representative live and SEM images A Amphimeniidae stet. (M12292) B Dorymenia stet. (M11997) C Dorymenia stet. (M16156, SEM) D Pruvotinidae stet. (M16880) E Pruvotinidae stet. (M16885, SEM) F Stenosemus sp. SIO_BIC_M12017 (M12017) G Stenosemus sp. SIO_BIC_M17044 (M17044) H Tripoplax balaenophila (M16186). Scale bars: 1 mm (A, B, D, F–H); 0.1 mm (C); 0.02 mm (E).

Material examined. AD4587: M12292 (PQ449404).

Localities. Mound 12 (996 m).

Mollusca | Solenogastres | Proneomeniidae

Dorymenia stet.

Fig. 42B, C

Material examined. AD4505: M11997; AD4917: M16156 (PQ435554; 16S: PQ304662).

Localities. Mound 12 (1002 m), Mound 11 (~ 1019–1025 m).

Remarks. M11997 and M16156 are the same morphospecies. M16156 was associated with the octocoral Swiftia sahlingi (Co2935).

Mollusca | Solenogastres | Pruvotinidae

Pruvotinidae stet.

Fig. 42D, E

Material examined. AD4978: M16880, M16885 (PQ435555).

Localities. Mound 12 (997 m).

Remarks. M16880 was associated with a hydroid (Co3639).

Mollusca | Polyplacophora | Chitonida | Ischnochitonidae

Stenosemus sp. SIO_BIC_M12017

Fig. 42F

Material examined. AD4508: M12017 (16S: PQ304661).

Localities. Parrita Seep (1402 m).

Remarks. An undescribed species.

Stenosemus sp. SIO_BIC_M17044

Fig. 42G

Material examined. S0218: M17044 (PQ449420).

Localities. Parrita Scar (1364 m).

Remarks. An undescribed species.

Tripoplax balaenophila (Schwabe & Sellanes, 2004)

Fig. 42H

Material examined. AD4512: M12064 (PQ450384; 16S: PQ304667); AD4918: M16186.

Localities. Quepos Slide (338 m and ~ 344–411 m).

Distribution. Originally described from whale bones at 240 m, within the oxygen minimum zone, off Concepción, central Chile (36°29.9'S, 73°40.8'W) (Schwabe and Sellanes 2004). Specimens identified as Tripoplax cf. balaenophila have been collected off central Baja California, 530–625 m, in hypoxic conditions near the lower boundary of the oxygen minimum zone (Suárez-Mozo and Hendrickx 2016). Those specimens show morphological variations from the T. balaenophila type material and require further taxonomic investigation, including genetic work, to determine whether they represent a range extension of T. balaenophila or a very similar undescribed species (Suárez-Mozo and Hendrickx 2016).

New records. Pending confirmation of the specimens from Mexico, our CRM specimens represent new northern records, new seep records, and a new maximum depth record for this species (specimen M12064, using 344 m as the most conservative value).

Remarks. Consistent with the previous reports of this species in hypoxic conditions, the CRM seep specimens were also collected within the oxygen minimum zone, although not in association with organic falls.

Mollusca | Polyplacophora | Lepidopleurida | Leptochitonidae

Leptochiton is paraphyletic and molecular taxonomic revision is needed (Irisarri et al. 2020).

Belknapchiton halistreptus (Dall, 1902)

Fig. 43A

Figure 43. 

Mollusca: Polyplacophora, Bryozoa, and Entoprocta, representative live images A Belknapchiton halistreptus (M17045) B Hanleyella sp. SIO_BIC_M11969 (M11969) C Leptochiton cf. americanus (M12016) D Leptochiton cf. incongruus (M17067) E Leptochiton sp. SIO_BIC_M17068 (M17068; specimen length estimated < 3 mm, maximum 6 mm) F Bryozoa stet. (Ep220) G Entoprocta stet. (BI1162) H Entoprocta stet. (BI1166, detail). Scale bars: 1 mm.

Material examined. S0219: M17045 (PQ449421).

Localities. Rio Bongo Scar (609 m).

Distribution. Known only from the type locality off Acapulco, Mexico, 902–3436 m (Dall 1902, 1908; Sirenko et al. 2022). Two subspecies are distinguished by morphology and depth: B. halistreptus halistreptus from ~ 3400 m and B. halistreptus abbreviatus from ~ 900–1200 m (Dall 1908; Sirenko et al. 2022).

New records. The CRM specimen represents a new southern record and a new minimum depth record for this species.

Remarks. B. halistreptus is a member of the recently described genus Belknapchiton Sirenko, Saito & Schwabe, 2022. This genus of 22 species includes many of the worldwide chiton specimens obtained from deep water that were formally assigned to Leptochiton, and these generally require SEM observations to identify to species. The type species, B. belknapi (Dall, 1878), was described from 1840 m off the western Aleutian Islands and is widespread at depths of 100–3724 m in the Pacific, from the Izu-Ogasawara Trench through the Bering Sea and eastern Pacific as far south as central Chile (Sirenko and Sellanes 2016; Sirenko et al. 2022). The CRM specimen has been tentatively identified as one of two similar subspecies of B. halistreptus. Both subspecies can be distinguished from B. belknapi and other congeners because they have ~ 2× as many gills as B. belknapi and a gill row that extends further anterior to approximately the position of the fifth valve (Sirenko et al. 2022).

Hanleyella sp. SIO_BIC_M11969

Fig. 43B

Material examined. AD4501: M11969 (16S: PQ304660); AD4508: M12015; AD4588: M12131; AD4974: M16766, M16767; AD4978: M16841, M16842, M16883, M16884; AD4987: M16905.

Localities. Mound 12 (~ 1000 m), Parrita Seep (1402 m).

Remarks. These specimens represent an undescribed species with morphological and genetic similarities to H. oldroydi (Dall, 1919), which is found from Alaska to Baja California at depths of 18–455 m (Stebbins and Eernisse 2009).

Leptochiton cf. americanus Kaas & Van Belle, 1985

Fig. 43C

Material examined. AD4508: M12016; AD4973: M16725; AD4976: M16814; S0230: M17101, M17104, M17107 (PQ449425).

Localities. Parrita Seep (1419 m), Jacó Scar (1887 m), Mound Jaguar (1896–2000 m).

Remarks. All specimens except M16725 were associated with naturally occurring or experimentally deployed wood. These specimens may represent an undescribed species or new depth records of L. americanus, which was originally described from the Gulf of Panama, 1188 m, and is known from Oregon to Chile, 311–1400 m (Schwabe and Sellanes 2010).

Leptochiton cf. incongruus (Dall, 1908)

Fig. 43D

Material examined. S0219: M17067 (PQ449422).

Localities. Rio Bongo Scar (661 m).

Remarks. Associated with a naturally occurring wood fall. Possibly an undescribed species or a juvenile of L. incongruus, which was described from the Gulf of Panama, 589 m (Dall 1908).

Leptochiton sp. SIO_BIC_M17068

Fig. 43E

Material examined. S0219: M17068 (PQ449423; no voucher remaining after DNA extraction).

Localities. Rio Bongo Scar (661 m).

Remarks. An undescribed species associated with a naturally occurring wood fall.

Bryozoa

Bryozoa stet.

Fig. 43F

Material examined. AD4591: Ep245; AD4924: Ep220.

Localities. Parrita Seep (~ 1400–1410 m), Jacó Scar (~ 1752–1795 m).

Remarks. Encrusting on vesicomyid clams.

Entoprocta

Entoprocta stet.

Fig. 43G, H

Material examined. AD4919: BI1162; AD4921: BI1166.

Localities. Quepos Slide (~ 345–397 m).

Remarks. BI1162 was associated with the tube of a sabellid worm, Pseudopotamilla stet. (A8390). BI1166 was associated with a naturally occurring wood fall.

Platyhelminthes

Fecampiida stet.

Fig. 44A, B

Figure 44. 

Platyhelminthes, Chaetognatha, Nematoda, and Arthropoda: Pycnogonida, representative live images A Fecampiida stet. (Pt64, egg cocoon) B Fecampiida stet. (Pt64, detail of eggs) C Rhabditophora stet. (Pt72) D Chaetognatha stet. (BI1347) E Nematoda stet. (Nto35) F Colossendeis macerrima (C12792, wide view) G Colossendeis macerrima (C11151, detail) H Colossendeis stet. (C13919, wide view). Scale bars: 1 cm (A, H); 0.1 mm (B); 1 mm (C–E, G); 10 cm (F).

Material examined. AD4916: Pt64.

Localities. Jacó Scar (1854 m).

Remarks. This coiled cocoon of egg capsules was found on soft sediment. Fecampiid cocoons have been previously reported in association with gorgonians in the western Pacific, 92–295 m (Handl and Bouchet 2007).

Rhabditophora stet.

Fig. 44C

Material examined. AD4978: Pt66; AD4985: Pt68; AD4989: Pt72, Pt73.

Localities. Mound 12 (~ 995–1002 m), Jacó Scar (1768 m).

Remarks. Pt72 and Pt73 were associated with a tubeworm bush.

Chaetognatha

Chaetognatha stet.

Fig. 44D

Material examined. AD4985: BI1347.

Localities. Mound 12 (991 m).

Nematoda

Nematoda stet.

Fig. 44E

Material examined. AD4918: Nto35; AD4979: Nto64, Nto65, Nto66, Nto67; S0216: Nto68.

Localities. Quepos Slide (~ 275–400 m).

Arthropoda

We list the major arthropod clades according to the phylogenetic relationships in Regier et al. (2010). See Azofeifa-Solano and Cortés (2020) for a detailed review of deep-sea crustaceans recorded from Costa Rican waters.

Many of the copepod, barnacle, and peracarid morphospecies in this study were represented by small single specimens and may represent undescribed species. To minimize the destruction of diagnostic features, we did not attempt extensive genetic investigation. Specimens are available for loan for future examination.

Arthropoda | Chelicerata | Pycnogonida

We list entries following the phylogeny in Ballesteros et al. (2021). We thank Claudia Arango (Queensland Museum) for assistance with morphological identification of these specimens.

Arthropoda | Chelicerata | Pycnogonida | Colossendeidae

Colossendeis macerrima Wilson, 1881

Fig. 44F, G

Material examined. AD4509: C11151; AD4914: C12792 (PQ449344).

Localities. Jacó Scar (~ 974–1856 m).

Distribution. Considered cosmopolitan (Munilla and Soler Membrives 2009), originally described from the United States mid-Atlantic coast, 1686 m (Wilson 1881), and previously reported from the Pacific coast of Central America (Hendrickx 2020b).

Remarks. The COI sequence of C12792 was 93.19–95.94% identical to sequences of Colossendeis macerrima (KF603929.1, KF603928.1, JN018213.1, FJ862873.1), with the closest BLASTN matches corresponding to specimens from southern Chile, 510 m (Weis and Melzer 2012). We interpret this 4–7% divergence as intraspecific variation, based on a previous analysis of C. macerrima and nine other Chilean pycnogonid species, in which the maximum intraspecific COI divergence was 10.4% and the minimum interspecific COI divergence was 13.36% (Weis and Melzer 2012).

Colossendeis stet.

Figs 44H, 45A

Figure 45. 

Arthropoda: Pycnogonida and Copepoda, representative live images A Colossendeis stet. (C13919, detail) B Sericosura sp. SIO_BIC_C13774 (C13774) C Sericosura sp. SIO_BIC_C13775 (C13775) D Anoplodactylus gen. inc. (C13825, wide view) E Anoplodactylus gen. inc. (C13825, detail) F Bradophilidae stet. (A1451) G Cyclopoida sp. SIO_BIC_C12780 (C12780, dorsal view) H Cyclopoida sp. SIO_BIC_C12780 (C12780, ventral view). Scale bars: 1 cm (A); 1 mm (B–H).

Material examined. S0218: C13919 (PQ449356).

Localities. Parrita Scar (1153 m).

Remarks. An amphipod, Mesopleustes abyssorum (C13920), was attached to the palp of this specimen. The closest COI BLASTN results on GenBank were several species of Colossendeis with ~ 88% identity, e.g., C. colossea Wilson, 1881 (FJ716626.1, formerly C. gigas Hoek, 1881), C. australis Hodgson, 1907 (GQ387003.1), C. tortipalpis Gordon, 1932 (KT202204.1), and C. macerrima (JN018213.1). This level of COI divergence falls between the intraspecific (<10.4%) and interspecific (>13.36%) divergences reported for other pycnogonids (Weis and Melzer 2012), so species-level identification of the CRM specimen will require further investigation.

Arthropoda | Chelicerata | Pycnogonida | Ammotheidae

Sericosura sp. SIO_BIC_C13774

Fig. 45B

Material examined. AD4972: C13774 (PQ449350).

Localities. Jacó Scar (1795 m).

Remarks. An undescribed species.

Sericosura sp. SIO_BIC_C13775

Fig. 45C

Material examined. AD4972: C13775 (PQ449351); AD4989: C13865.

Localities. Jacó Scar (1785–1795 m).

Remarks. An undescribed species.

Arthropoda | Chelicerata | Pycnogonida | Phoxichilidiidae

Anoplodactylus gen. inc.

Fig. 45D, E

Material examined. AD4978: C13793 (PQ449353); AD4985: C13825.

Localities. Mound 12 (~ 996–1002 m).

Remarks. Most likely Anoplodactylus, perhaps an undescribed species (Claudia Arango, pers. comm. 24 July 2022).

Arthropoda | Crustacea | Copepoda

We thank Linsey Sala (Scripps Institution of Oceanography Pelagic Invertebrate Collection) for assistance with these identifications.

Arthropoda | Crustacea | Copepoda | Cyclopoida

Bradophilidae stet.

Fig. 45F

Material examined. AD4511: C14958 (no material remaining); AD4987: C14494.

Localities. Mound 12 (~ 988–1012 m).

Remarks. Egg masses were attached to the flabelligerid Bradabyssa cf. pilosa: C14958 on host A1451 and C14494 on host A9840.

Cyclopoida sp. SIO_BIC_C12780

Fig. 45G, H

Material examined. AD4503: C11138; AD4587: C11184; AD4910: C12780 (PQ449343).

Localities. Mound 12 (~ 1000 m).

Remarks. Found in the mantle cavity of the solemyid clam Acharax cf. johnsoni: C11138 with clam M11980, C12780 with clam M15768.

Cyclopoida sp. SIO_BIC_C12807

Fig. 46A

Figure 46. 

Arthropoda: Copepoda and Cirripedia, representative live images A Cyclopoida sp. SIO_BIC_C12807 (C12807) B Harpacticoida stet. (C13870) C Rhizocephala sp. SIO_BIC_C13776 (C13776) D Rhizocephala sp. SIO_BIC_C13875 (C13875) E Litoscalpellum sp. SIO_BIC_C11143 (C11143) F Litoscalpellum sp. SIO_BIC_C12782 (C12782) G Scalpellidae sp. SIO_BIC_C13851 (C13851) H Metaverruca gen. inc. (C11148). Scale bars: 1 mm (A, B, D, E, G, H); 1 cm (C, F).

Material examined. AD4918: C12807.

Localities. Quepos Slide (~ 333–408 m).

Arthropoda | Crustacea | Copepoda | Harpacticoida

Harpacticoida stet.

Fig. 46B

Material examined. AD4988: C13870.

Localities. Mound 11 (~ 1005–1025 m).

Arthropoda | Crustacea | Copepoda | Siphonostomatoida

Caligus stet.

Material examined. AD4503: MZUCR-2770-01 (no images available); AD4505: MZUCR-2771-01 (no images available).

Localities. Mound 11 (~ 1020 m), Mound 12 (~ 1000 m).

Arthropoda | Crustacea | Thecostraca | Cirripedia

We list entries following the phylogeny in Chan et al. (2021). We thank Hiromi Watanabe (Japan Agency for Marine-Earth Science and Technology) for the morphology-based identifications.

Arthropoda | Crustacea | Thecostraca | Cirripedia | Rhizocephala

Rhizocephala sp. SIO_BIC_C13776

Fig. 46C

Material examined. AD4975: C13776 (PQ448998).

Localities. Mound 12 (1000 m).

Remarks. Parasite of a lithodid crab, Lithodes panamensis (C13787). The closest COI BLASTN results on GenBank were within Peltogastridae: Briarosaccus sp. (OR466125.1, 84.23% identity), Peltogaster boschmai Reinhard, 1944 from the San Juan Islands, Washington, USA (MN138416.1, 80.00% identity), and several sequences of P. lineata Shiino, 1943 from Korea and Japan (e.g., MK604142.1, 78.82% identity).

Rhizocephala sp. SIO_BIC_C13875

Fig. 46D

Material examined. AD4989: C13875 (PQ449355).

Localities. Jacó Scar (1762 m).

Remarks. Parasite of a squat lobster, Munidopsis alvisca (C13876). The closest COI BLASTN results on GenBank were several species of Lernaeodiscus (Peltogastridae), e.g., L. ingolfi Boschma, 1928 from Norway (MN605966.1, 80.62% identity) and L. rybakovi Korn, Golubinskaya, Rees, Glenner & Høeg, 2020 from Vostok Bay, Russia (MN605964.1, 78.81% identity).

Arthropoda | Crustacea | Thecostraca | Cirripedia | Thoracica | Scalpellomorpha

Litoscalpellum sp. SIO_BIC_C11143

Fig. 46E

Material examined. AD4504: C11143.

Localities. Mound 11 (~ 1004–1011 m).

Remarks. Attached to a vestimentiferan tubeworm. Litoscalpellum is polyphyletic and revision is required (Linse et al. 2013).

Litoscalpellum sp. SIO_BIC_C12782

Fig. 46F

Material examined. AD4913: C12782.

Localities. Jacó Scar (1885 m).

Scalpellidae sp. SIO_BIC_C13851

Fig. 46G

Material examined. AD4990: C13851.

Localities. Parrita Seep (1401 m).

Arthropoda | Crustacea | Thecostraca | Cirripedia | Thoracica | Verrucomorpha

Metaverruca gen. inc.

Fig. 46H

Material examined. AD4508: C11148.

Localities. Parrita Seep (~ 1401–1419 m).

Remarks. Likely Metaverruca. Attached to a tubeworm, Lamellibrachia barhami.

Newmaniverruca gen. inc.

Fig. 47A

Figure 47. 

Arthropoda: Cirripedia, Stomatopoda, and Amphipoda, representative images. Live specimens are depicted unless otherwise specified A Newmaniverruca gen. inc. (C12794) B Verrucidae sp. SIO_BIC_C11144 (C11144) C Pyrgomatidae stet. (C12815) D Squilla biformis (C13807, dorsal view) E Squilla biformis (C13807, ventral view) F Hyperiidea stet. (C15409, preserved specimen) G Lycaea pulex (C14397) H Mesopleustes abyssorum (C13920). Scale bars: 1 mm (A–C, F, G); 1 cm (D, E, H).

Material examined. AD4916: C12794.

Localities. Jacó Scar (1611 m).

Remarks. Likely Newmaniverruca.

Verrucidae sp. SIO_BIC_C11144

Fig. 47B

Material examined. AD4506: C11144.

Localities. Parrita Seep (~ 1030–1179 m).

Remarks. Likely Altiverruca or Newmaniverruca.

Arthropoda | Crustacea | Thecostraca | Cirripedia | Thoracica | Balanomorpha

Pyrgomatidae stet.

Fig. 47C

Material examined. AD4923: C12815.

Localities. Parrita Seep (~ 1041–1094 m).

Remarks. Associated with a coralliid (Co2947).

Arthropoda | Crustacea | Malacostraca | Hoplocarida | Stomatopoda | Squillidae

Squilla biformis Bigelow, 1891

Fig. 47D, E

Reference. Koga and Rouse (2021) for the mitochondrial genome and phylogenetic analysis of C13808.

Material examined. AD4979: C13807 (PQ449354), C13808 (MW867305); AD4986: MZUCR-3732-01.

Localities. Quepos Slide (~ 380–395 m).

Distribution. Originally described from La Paz, Gulf of California, at 205 m (Bigelow 1894) and distributed south to Peru at depths of 28–518 m (Hendrickx and Salgado-Barragán 1991; Hendrickx and López 2020). S. biformis has been studied from Pacific Costa Rica at depths of 131–350 m (Camp and Kuck 1990; Wehrtmann and Echeverría-Sáenz 2007; Hernáez et al. 2011; Azofeifa-Solano and Cortés 2020).

Remarks. Telson morphology indicates that both specimens are female. To our knowledge this study is the first report of this well-known local species in the vicinity of seeps, notably within the oxygen minimum zone as characterized by Levin et al. (2015).

Arthropoda | Crustacea | Malacostraca | Peracarida

Several available checklists of eastern Pacific deep-sea peracarids (Hendrickx 2020a) may be informative for future work on these specimens. Unless otherwise stated, we list entries following the phylogenies in Schwentner et al. (2018) and Höpel et al. (2022).

Arthropoda | Crustacea | Malacostraca | Peracarida | Lophogastrida

Eucopia sculpticauda Faxon, 1893

Material examined. AD4513: MZUCR-2818-01 (no image available).

Localities. Jacó Scar (~ 1800 m).

Distribution. Originally described from several stations in the Gulf of Panama and off the Galápagos Islands, 1618–2487 m (Faxon 1893, 1895). Reported with a wide latitudinal distribution in the Indo-Pacific and Atlantic Oceans, from ~ 1000–7526 m depth (Kou et al. 2019).

Arthropoda | Crustacea | Malacostraca | Peracarida | Amphipoda

We list entries following the World Amphipoda Database (Horton et al. 2022), acknowledging the need for further systematic work as discussed in the molecular phylogeny of Copilaş-Ciocianu et al. (2020).

Arthropoda | … | Amphipoda | Hyperiidea

We thank Linsey Sala for these identifications.

Hyperiidea stet.

Fig. 47F

Material examined. AT15-59 Plankton Tow 6: C15409.

Localities. Jacó Summit (~ 350 m depth, ~ 400 m above the seafloor).

Lycaea pulex Marion, 1874

Fig. 47G

Material examined. AT15-59 Plankton Tow 6: C14397.

Localities. Jacó Summit (~ 350 m depth, ~ 400 m above the seafloor).

Distribution. Considered common and widespread in tropical to warm-temperate oceans worldwide, typically 0–500 m depth (Zeidler 2021).

Arthropoda | … | Amphipoda | Amphilochidea | Amphilochida | Amphilochidira | Amphilochoidea | Pleustidae

Mesopleustes abyssorum (Stebbing, 1888)

Fig. 47H

Material examined. S0218: C13920.

Localities. Parrita Scar (1153 m).

Distribution. Originally described from the subantarctic Indian Ocean off South Africa, 2926 m (Stebbing 1888), M. abyssorum is considered “probably cosmopolitan” at depths below ~ 700 m (Barnard 1967). In the eastern Pacific, M. abyssorum has been reported from 3479 m off Baja California (Barnard 1967).

Remarks. Observed in situ attached to the palp of a pycnogonid, Colossendeis macerrima (C13919) and remained attached after collection.

Stenopleustes gen. inc.

Fig. 48A

Figure 48. 

Arthropoda: Amphipoda, representative images. Live specimens are depicted unless otherwise specified A Stenopleustes gen. inc. (C12811) B Seba stet. (C13970) C Stenothoe sp. SIO_BIC_C13857 (C13857) D Stenothoe sp. SIO_BIC_C13867 (C13867) E Stenula stet. (C13784, preserved specimen) F Rhachotropis stet. (C13798) G Idunella gen. inc. (C13856) H Monoculodes stet. (C12801, preserved specimen). Scale bars: 1 mm.

Material examined. AD4507: C11146 (PQ450405), C14496; AD4916: C12788; AD4922: C12811.

Localities. Mound 12 (~ 967 m), Jacó Scar (~ 1852–1855 m), Parrita Scar (~ 1659–1667 m).

Remarks. C12811 was associated with an antipatharian coral (specific host not recorded). This morphospecies was identified as most likely Stenopleustes (Pleustidae), but an alternative identification is Stenothoidae. More detailed morphological examination of vouchers is needed.

Arthropoda | … | Amphipoda | Amphilochidea | Amphilochida | Amphilochidira | Amphilochoidea | Sebidae

Seba stet.

Fig. 48B

Material examined. S0230: C13970.

Localities. Mound Jaguar (1896 m).

Remarks. Associated with a naturally occurring wood fall.

Arthropoda | … | Amphipoda | Amphilochidea | Amphilochida | Amphilochidira | Amphilochoidea | Stenothoidae

Stenothoe sp. SIO_BIC_C13857

Fig. 48C

Material examined. AD4985: C13857.

Localities. Mound 12 (991 m).

Remarks. This morphospecies lacks eyes.

Stenothoe sp. SIO_BIC_C13867

Fig. 48D

Material examined. AD4987: C13867.

Localities. Mound 12 (999 m).

Remarks. This morphospecies has eyes.

Stenula stet.

Fig. 48E

Material examined. AD4974: C13784.

Localities. Mound 12 (992 m).

Remarks. Associated with experimental deployments of bone and wood.

Arthropoda | … | Amphipoda | Amphilochidea | Amphilochida | Eusirida | Eusiroidea | Eusiridae

Rhachotropis stet.

Fig. 48F

Material examined. AD4507: C14497; AD4976: C13798.

Localities. Jacó Scar (1887 m), Parrita Scar (~ 1659–1667 m).

Remarks. Specimen C13798 may have been associated with experimentally deployed wood.

Arthropoda | … | Amphipoda | Amphilochidea | Amphilochida | Eusirida | Liljeborgioidea | Liljeborgiidae

Idunella gen. inc.

Fig. 48G

Material examined. AD4985: C13856.

Localities. Mound 12 (991 m).

Remarks. This morphospecies has eyes. It is most likely Idunella (Liljeborgiidae), but an alternative identification is Stenopleustes (Pleustidae). Further morphological examination is needed.

Arthropoda | … | Amphipoda | Amphilochidea | Amphilochida | Oedicerotidira | Oedicerotoidea | Oedicerotidae

Monoculodes stet.

Fig. 48H

Material examined. AD4507: C14495; AD4589: C11188 (PQ449341); AD4917: C12785; AD4922: C12801.

Localities. Mound 12 (965–997 m), Parrita Scar (~ 1659–1667 m).

Remarks. C12785 was associated with the antipatharian coral Lillipathes ritamariae. C12801 was associated with a basket star, Gorgonocephalus stet. (E7064).

Arthropoda | … | Amphipoda | Amphilochidea | Lysianassida | Haustoriidira | Haustorioidea | Phoxocephalidae

Phoxocephalinae subfam. inc.

Fig. 49A

Figure 49. 

Arthropoda: Amphipoda, representative images. Live specimens are depicted unless otherwise specified A Phoxocephalinae subfam. inc. (C13858) B Ambasiella stet. (C13917, preserved specimen) C Orchomene stet. (C13972) D Tryphosidae stet. (C13854) E Ambasiopsis stet. (C13790, preserved specimen) F Stegocephalidae stet. (C13976, preserved specimen) G Lepechinella stet. (C13929, preserved specimen) H Pardalisca stet. (C13928, preserved specimen). Scale bars: 1 mm.

Material examined. AD4984: C13858.

Localities. Mound 12 (998 m).

Arthropoda | … | Amphipoda | Amphilochidea | Lysianassida | Lysianassidira | Aristioidea | Ambasiidae

Ambasiella stet.

Fig. 49B

Material examined. S0218: C13917.

Localities. Parrita Scar (1988 m).

Remarks. Associated with a xenophyophore.

Arthropoda | … | Amphipoda | Amphilochidea | Lysianassida | Lysianassidira | Lysianassoidea | Tryphosidae

Orchomene stet.

Fig. 49C

Material examined. S0230: C13972, C13977.

Localities. Mound Jaguar (1895–1909 m).

Tryphosidae stet.

Fig. 49D

Material examined. AD4974: C13785; AD4985: C13854.

Localities. Mound 12 (992–1002 m).

Remarks. C13785 was associated with experimental deployments of bone and wood.

Arthropoda | … | Amphipoda | Amphilochidea | Lysianassida | Lysianassidira | Lysianassoidea incertae sedis

Ambasiopsis stet.

Fig. 49E

Material examined. AD4972: C13789, C13790.

Localities. Jacó Scar (1845 m).

Remarks. Associated with experimentally deployed pig bones.

Arthropoda | … | Amphipoda | Amphilochidea | Lysianassida | Lysianassidira | Stegocephaloidea | Stegocephalidae

Stegocephalidae stet.

Fig. 49F

Material examined. S0230: C13976, C13978.

Localities. Mound Jaguar (1895–1908 m).

Arthropoda | … | Amphipoda | Amphilochidea | Lysianassida | Synopiidira | Dexaminoidea | Lepechinellidae

Lepechinella stet.

Fig. 49G

Material examined. S0219: C13929.

Localities. Rio Bongo Scar (~ 480–650 m).

Arthropoda | … | Amphipoda | Amphilochidea | Lysianassida | Synopiidira | Dexaminoidea | Pardaliscidae

Pardalisca stet.

Fig. 49H

Material examined. S0219: C13928.

Localities. Rio Bongo Scar (661 m).

Remarks. Associated with a naturally occurring wood fall.

Arthropoda | … | Amphipoda | Amphilochidea | Lysianassida | Synopiidira | Synopioidea | Argissidae

Argissa sp. SIO_BIC_C13930

Fig. 50A

Figure 50. 

Arthropoda: Amphipoda, representative images. Live specimens are depicted unless otherwise specified A Argissa sp. SIO_BIC_C13930 (C13930, preserved specimen) B Bonnierella stet. (C13797) C Gammaropsis gen. inc. (C13963, preserved specimen) D Bemlos gen. inc. (C13931, preserved specimen) E Protomedeiinae stet. (C14396) F Oradarea stet. (C13796) G Abludomelita gen. inc. (C11141) H Abludomelita stet. (C13896). Scale bars: 1 mm (A–G); 1 cm (H).

Material examined. S0219: C13930.

Localities. Rio Bongo Scar (~ 480–650 m).

Remarks. Possibly an undescribed species, requiring further comparison. Argissa is currently accepted as monotypic, with Argissa hamatipes (Norman, 1869) reportedly occurring across the northern hemisphere at depths of 4–1096 m (Barnard 1967; Winfield et al. 2020). A specimen provisionally identified as A. hamatipes has been recorded from western Mexico, minimum depth 1720 m (Barnard 1967).