Abyssal fauna of the UK-1 polymetallic nodule exploration area, Clarion-Clipperton Zone, central Pacific Ocean: Mollusca

Abstract We present the first DNA taxonomy publication on abyssal Mollusca from the Clarion-Clipperton Zone (CCZ), central Pacific ocean, using material collected as part of the Abyssal Baseline (ABYSSLINE) environmental survey cruise ‘AB01’ to the UK Seabed Resources Ltd (UKSRL) polymetallic-nodule exploration area ‘UK-1’ in the eastern CCZ. This is the third paper in a series to provide regional taxonomic data for a region that is undergoing intense deep-sea mineral exploration for high-grade polymetallic nodules. Taxonomic data are presented for 21 species from 42 records identified by a combination of morphological and genetic data, including molecular phylogenetic analyses. These included 3 heterodont bivalves, 5 protobranch bivalves, 4 pteriomorph bivalves, 1 caudofoveate, 1 monoplacophoran, 1 polyplacophoran, 4 scaphopods and 2 solenogastres. Gastropoda were recovered but will be the subject of a future study. Seven taxa matched published morphological descriptions for species with deep Pacific type localities, and our sequences provide the first genetic data for these taxa. One taxon morphologically matched a known cosmopolitan species but with a type locality in a different ocean basin and was assigned the open nomenclature ‘cf’ as a precautionary approach in taxon assignments to avoid over-estimating species ranges. One taxon is here described as a new species, Ledella knudseni sp. n. For the remaining 12 taxa, we have determined them to be potentially new species, for which we make the raw data, imagery and vouchers available for future taxonomic study. The Clarion-Clipperton Zone is a region undergoing intense exploration for potential deep-sea mineral extraction. We present these data to facilitate future taxonomic and environmental impact study by making both data and voucher materials available through curated and accessible biological collections.


Introduction
The abyssal zone of the world's oceans has been defined as that between 3000 m and 6000 m depth, a bathymetric zone that encompasses 54% of the geographic surface of the planet (Smith et al. 2008). Molluscs form a characteristic and abundant group in this region, and many of them, most prominently among the bivalves, are deposit feeders that can sustain themselves on the steady rain of organic matter from surface regions. Current online databases list 1204 mollusc species recorded at abyssal depths from between 3000 m and 6000 m (OBIS 2017) out of a total of 3229 accepted 'deepsea' mollusc species recorded from depths greater than 500 m (Glover et al. 2017).
The Clarion-Clipperton Zone (hereafter, CCZ) is so called as it lies between the Clarion and Clipperton Fracture Zones, topographical highs that extend longitudinally across almost the entire Pacific Ocean. There is no strict definition of the region, but it has come to be regarded as the area between these fracture zones that lies within international waters and encompasses the main areas of commercial interest for polymetallic nodule mining. Exploration licenses issued by the International Seabed Authority (ISA 2017) extend from 115°W (the easternmost extent of the UK-1 exploration area) to approximately 158°W (the westernmost extent of the COMRA exploration area), as such we use from hereafter a working definition of the CCZ as the box: 13°N158°W; 18°N118°W; 10°N112°W; 2°N155°W. This is an area of almost exactly 5 million sq km, approximately 1.4% of the ocean's surface.
The Challenger expedition between 1872 and 1876 is said to be the start of modern oceanography, and in total about 4700 new species were described from it. However, in the Pacific Ocean they went from Japan to the Hawaiian Islands and after that fairly straight south down to about 40°S where they turned towards Valparaiso in Chile, and thus they did only touch the western-most part of the CCZ (Tizard et al. 1885). From 1891 to 1905 Agassiz did three expeditions onboard Albatross, after which Dall described 218 new species of molluscs and brachiopods from off the coast of Central and South America (Dall 1908). The Danish Galathea II deep-sea expedition went around the world in 1950-1952, but in the Pacific they went from New Zealand to Hawaii and then up north towards San Fransisco (Bruun et al. 1956), and did not collect anything in the actual CCZ.
Within the entire 5 million sq km CCZ, as defined above, online databased sources prior to this publication list only one benthic mollusc record when specifying depth between 3000-6000 m, and a further four records just south of CCZ (OBIS 2017). This result is due to lack of sampling and/or taxonomic knowledge given that an abundant and diverse mollusc fauna is suspected in the region based on anecdotal reports from past environmental surveys (e.g. ISA 1999; Ebbe et al. 2010). The goal of the DNA taxonomy part of the Abyssal Baseline (ABYSSLINE) program is to start to rectify these gaps in our knowledge and make data publically available that will eventually allow for a complete taxonomic synthesis of the CCZ supported by openly-available molecular and morphological data. We present results from a DNA taxonomy survey of abyssal benthic Mollusca collected as part of the first ABYSSLINE environmental survey cruise 'AB01' to the UK Seabed Resources Ltd (UKSRL) polymetallic nodule exploration contract area 'UK-1' (Fig. 1) in the eastern Clarion-Clipperton Zone (CCZ), central Pacific Ocean (Smith et al. 2013). Here we provide the first version of the Mollusca taxonomic synthesis, consisting of taxon records, images, genetic data and short descriptions from the first research cruise (AB01) aboard the RV Melville in October 2013. Gastropoda is not included in this version (subject to a future study), and we report on Bivalvia, Caudofoveata, Monoplacophora, Polyplacophora, Scaphopoda and Solenogastres.
This paper aims to provide regional taxonomic information for an area that is undergoing intense deep-sea mineral exploration for high-grade polymetallic nodules regulated by Sponsoring States (here the United Kingdom Government) and the International Seabed Authority (ISA 2017). The study is not a comprehensive faunal guide to the region, but a taxonomic data paper that will be updated with new additions following future collections and analyses. This publication is supported by similar data publications on other taxa from the CCZ. Two have been published (Echinodermata, Glover et al. 2016b andCnidaria, Dahlgren et al. 2016), while other taxa are in preparation, forming a suite of taxonomic syntheses of biodiversity in the region, supported by a contract between the company UK Seabed Resources Ltd and the Natural History Museum, London and Uni Research, Bergen.

Materials and methods
Knowledge of baseline biodiversity and biogeography in the CCZ is severely hampered by a lack of modern DNA-supported taxonomic studies (Glover et al. 2016a). With this in mind, three fundamental principles underpin our methodological pipeline: (1) the careful sorting and collection of live samples at sea using a 'cold-chain' pipeline by trained taxonomists, (2) the use of combined multiple-marker DNA sequences and morphological data in phylogenetics-based species descriptions or re-descriptions/ records and (3) integrated data and sample management to push openly-available taxonomic data through online repositories linked to curated molecular and morphological collections in national museums.

Fieldwork
The ABYSSLINE environmental baseline survey consists of a series of 30 × 30 km survey boxes (strata), three within the UK-1 exploration area, and an additional reference site outside the exploration area (Smith et al. 2013). Within each survey box, sample sites for a variety of benthic sampling gears are selected randomly -a randomized, stratified sampling design that assumes no a priori knowledge of the benthic environment. The UK-1 strata are being sampled in a series of oceanographic cruises during the course of the project, which commenced in July 2013, with the first cruise (AB01) taking place in October 2013 aboard the RV Melville (hereafter, cruise 'AB01'). During this cruise, the first stratum was comprehensively mapped and sampled for a range of environmental and geophysical parameters (Fig. 1, Smith et al. 2013).
A comprehensive description of our DNA taxonomy pipeline is provided in Glover et al. (2016a). In summary, deep-sea benthic specimens from the AB01 strata were collected using a range of oceanographic sampling gears including box core (BC), epibenthic sledge (EBS), remotely operated vehicle (ROV) and multiple core (MC). Geographic data from sampling activities was recorded on a central GIS database (Fig. 1). Live-sorting of specimen samples was carried out aboard the RV Melville in a 'coldchain' pipeline, in which material was immediately transferred and maintained in chilled, filtered seawater held at 2-4°C. Specimens were preliminary identified at sea and imaged live using stereomicroscopes with attached digital cameras. The specimens were then transferred to individual microtube vials containing an aqueous solution of 80% non-denatured ethanol, numbered and barcoded into a database and kept chilled until return to the Natural History Museum, London.

Laboratory work
In the laboratory, specimens were re-examined using stereo and compound microscopes, identified and described to best possible taxonomic level with key morphological features photographed with digital cameras and a small tissue-sample taken for DNA extraction.
Extraction of DNA was done with DNeasy Blood and Tissue Kit (Qiagen) using a Hamilton Microlab STAR Robotic Workstation. About 1800 bp of 18S, 450 bp of 16S, and 650 bp of cytochrome c oxidase subunit I (COI) were amplified using primers listed in Table 1. PCR mixtures contained 1 µl of each primer (10 µM), 2 µl template DNA and 21 µl of Red Taq DNA Polymerase 1.1X MasterMix (VWR) in a mixture of total 25 µl. The PCR amplification profile consisted of initial denaturation at 95°C for 5 min, 35 cycles of denaturation at 94°C for 45 s, annealing at 55°C for 45 s, extension at 72°C for 2 min, and a final extension at 72°C for 10 min. PCR prod- ucts were purified using Millipore Multiscreen 96-well PCR Purification System, and sequencing was performed on an ABI 3730XL DNA Analyser (Applied Biosystems) at The Natural History Museum Sequencing Facility, using the same primers as in the PCR reactions plus two internal primers for 18S (Table 1). Overlapping sequence fragments were merged into consensus sequences using Geneious (Kearse et al. 2012) and aligned using MAFFT (Katoh et al. 2002) for 18S and16S, andMUSCLE (Edgar 2004) for COI, both programs used as plugins in Geneious, with default settings. Bayesian phylogenetic analyses (BA) were conducted with MrBayes 3.2 (Ronquist et al. 2012). Analyses were run for 10-30 million generations, of which the first 25% generations were discarded as burn-in.

Data handling
The field and laboratory work created a series of databases and sample sets that are integrated into a data-management pipeline. This includes the transfer and management of data and samples between a central collections database, a molecular collections database and external repositories (GenBank, WoRMS, OBIS, GBIF, ZooBank) through DarwinCore archive. This provides a robust data framework to support DNA taxonomy, in which openly-available data and voucher material is key to quality data standards. A further elaboration of the data pipeline is published in Glover et al. (2016a).

Taxonomic assignments
All future studies of biogeographic and bathymetric ranges, gene-flow, extinction risks, natural history, reproductive ecology, functional ecology and geochemical interactions of CCZ species are dependent on accurate identifications faciliated by taxonomy. This taxonomy is dependent on a sound theoretical underpinning -a species concept -coupled with the availability of both raw data and voucher samples. Here we use a phylogenetic species concept sensu Donoghue (1985) with species determined by DNA-based phylogenetic analysis and the recognition of distinct monophyletic groups as species.
For those taxa where the typical morphological data that allows determination of species are missing, we provide the lowest-level taxonomic name possible, but include determination with genetic data. All materials (vouchers including archived frozen tissue) and genetic data are accessible together with the morphological data presented in this paper. A full list of all taxa including Natural History Museum Accession Numbers, NHM Molecular Collection Facility (NHM-MCF) FreezerPro numbers and NCBI GenBank Accession numbers is provided in Table 2.   (Allen & Morgan, 1981). However, the type locality for this species is from the deep north Atlantic and no genetic data are available for comparison. No similar species is recorded from deep water of the eastern Pacific. Forms a unique monophyletic clade with two other cuspidariid species distinct from all other AB01 specimens (Fig. 5). No genetic matches on GenBank.

LINE record# NHMUK Acc# NHMUK MCF# Gen Bank#
Ecology. Found in polymetallic nodule province. Description. Minute, thin-shelled, translucent, anteriorly extended, longer than high, umbones posterior of mid-line, posteriorly angulate, antero-dorsal margin long, evenly curved, shell surface smooth. Gill with single demibranch of about 10 widely spaced filaments, ventral edge of the gill does not cover the body pouches. Foot relatively large with distal bulb (Fig. 3). NHM_180 length 1.1 mm.  Remarks. Forms a monophyletic clade with four other thyasirid species (Fig. 5) and distinct from all other AB01 specimens. No genetic matches on GenBank. Morphologically the species is similar in shape to abyssal thyasirid species (Thyasira inflata, T. transversa) from the south Atlantic described and placed in Thyasira (Mendicula) by Payne & Allen (1991) but not similar to the type species of Mendicula (Lucina) induta Hedley, 1907= M. memorata Iredale, 1924 or the widespread Mendicula ferruginosa (Forbes, 1844). No similarly shaped species has been recorded from the abyssal eastern Pacific.
Remarks. Vesicomya galatheae was described from off Costa Rica and Panama at 2950-3570 m. Morphologically similar to Vesicomya pacifica (Smith, 1885) holotype NHMUK 1887.2.9.2710-11 but Krylova et al. (2015) regard this as a northern Pacific species distinguished from V. galatheae by the shape, hinge teeth and number of siphonal tentacles. When comparing sequences from our CCZ specimens with the Vesicomya pacifica from Krylova et al. (2015), the K2P difference is 0.11. In the molecular tree (Fig. 5) it groups with a Kelliella species from the northwestern Atlantic and these two species form a sister clade to Calyptogena species. Kelliella species are very similar to Vesicomya and the relationships of species assigned to the two genera need clarification. Forms a unique monophyletic clade distinct from all other AB01 specimens. No genetic matches on GenBank.
Ecology. Found in polymetallic nodule province.
Remarks. Widely distributed in the eastern Pacific at depths of 400-5000 m (see Coan and Valentich-Scott 2012). The holotype (USNM 110573) was collected 725 km west of Trujillo, Peru at 2370 fathoms (4334 m). Forms a unique monophyletic clade distinct from all other AB01 specimens. Genetic match in 18S to Bathyspinula calcar (GenBank KC993875) from the north eastern Pacific (Sharma et al. 2013), but as the GenBank 18S sequence from B. calcar was only 289 bp long and as that specimen lacked COI, it was not included in the analyses. Some very small juvenile specimens (Fig. 6B-D) were recovered that superficially resemble Ledella knudseni sp. n. (Fig. 7) and may be easily confused. Genetic data confirmed these to be Bathyspinula calcar (Fig. 12). These may be distinguised from Ledella by the shiny and iridescent nature of the shell surface of B. calcar, which is preserved in the juveniles.
Remarks. Similar in form to Ledella ultima (Smith, 1885) widespread in the abyssal Atlantic (Allen 2008), but has a less massive hinge with more teeth, 8-9 compared with 6-8 in L. ultima. Also similar is the species identified by Knudsen (1970) as L. ultima from the Sunda Trench in Indian Ocean at 3810 m. The only species recorded from the deep eastern Pacific is Ledella dicella (Dall, 1908) from 734-1200 m off Ecuador but this lacks the short rostrum and has 12-13 hinge teeth on each side of the ligament (Coan and Valentich-Scott 2012 pl. 26). No genetic matches on GenBank. Ledella knudseni groups in a small subclade with but is distinct from the Atlantic species L. ultima and Ledella jamesi Allen & Hannah, 1989, as well as another Ledella species from this study in the Pacific, Ledella sp. (NHM_381) ( Figure  12). The new species can be confused with juveniles of B. calcar (see above), but shell is less shiny and iridescent, and ribs are more pronounced. DNA may be required to confirm identification.
Ecology. Found in polymetallic nodule province.
Remarks. This species is morphologically very similar to the new Ledella knudseni, its sister taxon in the molecular phylogenetic analyses (Fig. 12), and DNA might be required to properly identify the species. No genetic matches on GenBank.
Remarks. Extremely small, semi-transparent bivalves typically about 1 mm in size. Yoldiella species are particularly difficult to identify (see Killeen and Turner 2009). Forms a unique monophyletic clade distinct from all other AB01 specimens. No genetic matches on GenBank. In the molecular tree (Fig. 12) the genus Yoldiella is not monophyletic, and the present species does not group with another Eastern Pacific bathyal species, Yoldiella orcia (Dall, 1916), which instead forms a well-supported subclade with two Atlantic species.
Ecology. Found in polymetallic nodule province.
Ecology. Quite abundant. Found in polymetallic nodule province.
Genetic data. GenBank NHM_117 18S-MF157471. Knudsen (1970) and Coan & Valentich-Scott (2012). The holotype of D. panamensis was collected on the Galathea expedition (stn 726) at 3670-3270 m depth in Gulf of Panama. In the molecular analysis (Fig. 17) it aligns as a sister species to many shallow water Mytilidae. No genetic matches on GenBank.

Remarks. Identified from figures in
Ecology. Found in polymetallic nodule province. Description. Subcircular to slightly oblique with slightly sinuous posterior margin. Periostracum with short, fine, bristles aligned in radial rows. Ligament small, triangular, set in shallow resilifer. Hinge teeth robust, 4 anterior and 5 posterior. Inner shell margin smooth. Voucher NHM_453 shell length 4.6 mm, height 4.3mm (Fig. 15).
Genetic data. GenBank NHM_453 18S-MF157498, COI-MF157524. Remarks. Dissimilar in shape and periostracal bristle configuration to any recorded Eastern Pacific deep-water species (Coan & Valentich-Scott 2012). However, shape and number of hinge teeth are known to change with age/size in Limopsis species. In molecular analysis (Fig. 17) forms part of a well supported monophyletic clade with other Limopsis species and aligns closest to Limopsis marionensis Smith, 1885 from depths of 40-1000 m in the Southern Ocean. No genetic matches on GenBank.
Genetic data. GenBank NHM_105 18S-MF157469. Remarks. Holotype (ZMUC) from Gulf of Panama, 3270-3670 m Galathea stn 726, figured by Coan and Valentich-Scott (2012 pl. 100). In the molecular tree it groups with two other species of Propeamussidae on a long branch and distinct from other Pectinoida, but a GenBank species (VLG_2013) identified as Propeamussium sp. is distinct from these (Fig. 17). Henk H. Dijkstra (Naturalis Biodiversity Center in Leiden, Netherlands) advised on identification of this species. Forms a unique monophyletic clade distinct from all other AB01 specimens. No genetic matches on GenBank.
Ecology. Found in polymetallic nodule province. Description. Voucher NHM_344 (Fig. 18) partially broken aplacophoran mollusc, maximum width 0.8 mm, length of fragment ~2.5 mm. Posterior body end lacking. Anterior body intact, with indistinct neck region. Trunk partly damaged. Trunk sclerites are scales with a slender tip confluent with the broad blade without a distinct shoulder region. Tip with keel, triangular in cross section. Blade without sculpture. Data and material, including a permanent preparation of sclerites (1 slide), made available for future study.

Caudofoveata
Genetic data. GenBank NHM_344 16S-MF157462. Remarks. The specimen has the typical body shape and sclerite type of Prochaetodermatidae.
Ecology. Found in polymetallic nodule province. Burrows in soft sediment.
Remarks. Morphologically agrees with description of Veleropilina oligotropha (Rokop, 1972) described from ~6000 m water depth in the central North Pacific.
Forms a unique monophyletic clade distinct from all other AB01 specimens. No genetic matches on GenBank. In the molecular analyses based on the 16S gene, the Monoplacophora clade is strongly supported, but internal branches are unresolved or, when clades are present, they have low support (Fig. 20).
Ecology. Specimen collected from an epibenthic sledge tow across region of sediment and polymetallic nodules. Rokop (1972) did not observe the species directly on nodules, they were just recovered from the epibenthic sledge sample, as was the case in this study. The importance of the nodules as a habitat for the species remains uncertain until they are directly observed live on the seafloor. Material examined. NHM_446 NHMUK 20170073.1-2, collected 2013-10-20, 13.86367 -116.54432, 4050 m. http://data.nhm.ac.uk/object/d69b581d-8a79-4c4d-8f70-88b2ec07d86e Description. The form and pattern of tegmental granules together with the three aesthete pores are most similar to the images of Leptochiton macleani (Sirenko, 2015: figs 34-36). Voucher NHM_446 length approx 10 mm, width 3.2 mm (Fig. 21).
Remarks. Sirenko (2015) has recently reviewed Leptochiton of the southeastern Pacific Ocean and described several new species that had been previously confounded with Leptochiton belknapi Dall, 1878. The specimen morphologically matches Leptochiton macleani, type locality Peru-Chile Trench, East Pacific, 4600 m depth. Forms a unique monophyletic clade distinct from other AB01 specimens. No genetic matches on GenBank. In the molecular analyses based on the 18S and COI genes, it falls with strong support as sister taxon to two other Leptochiton species, but in the phylogenetic tree the genus Leptochiton is not monophyletic (Fig. 22).
Remarks. Forms a unique monophyletic clade distinct from other AB01 specimens. In the molecular analysis it groups with other Fissidentalium species, but with very low support. No genetic matches on GenBank. Phylogenetic tree supports placement in order Dentaliida, family Dentaliidae (Fig. 24). Genetic data and imagery provided to facilitate future study.
Ecology. Specimen collected from an epibenthic sledge tow across region of sediment and polymetallic nodules.
Genetic data. GenBank NHM_192 16S-MF157459, 18S-MF157483. Remarks. Forms a unique monophyletic clade distinct from other AB01 specimens. No genetic matches on GenBank. Phylogenetic tree (Fig. 24) supports placement in order Gadilida with NHM_345. Genetic and image data made available for future study when better specimens available.
Ecology. Specimen collected from an epibenthic sledge tow across region of sediment and polymetallic nodules.
Remarks. Forms a unique monophyletic clade distinct from other AB01 specimens. No genetic matches on GenBank. Phylogenetic tree supports placement in order Gadilida (Figure 24). Genetic and image data made available for future study when better specimens available.
Ecology. Specimen collected from an epibenthic sledge tow across region of sediment and polymetallic nodules.
Genetic data. GenBank NHM_132 16S-MF157456, 18S-MF157472. Remarks. Forms a unique monophyletic clade distinct from other AB01 specimens. No genetic matches on GenBank. Phylogenetic tree (Fig. 24) supports place- Figure 24. Phylogenetic analysis of Scaphopoda. 50% majority rule consensus tree from the Bayesian analyses using 18S. Asterisks denotes support values of 95 or above. ment in order Gadilida. Genetic and image data made available for future study when better specimens available.
Ecology. Specimen collected from an epibenthic sledge tow across region of sediment and polymetallic nodules.
Genetic data. GenBank NHM_367 COI-MF157519. Remarks. The combination of scales and hollow spicules as main epidermal sclerites is diagnostic for the family Acanthomeniidae. Forms a unique monophyletic clade distinct from other AB01 specimens (Fig. 27). No genetic matches on GenBank.
Ecology. Specimen collected from an epibenthic sledge tow across region of sediment and polymetallic nodules. Description. Voucher specimen NHM_027, small, probably juvenile, solenogaster specimen (Fig. 26). Main epidermal sclerites are very long hollow acicular spicules with simple pointed tips. Spicules slender, s-shaped and thin-walled; tips long and thin. Leaf-shaped pedal scales present. Data and material, including a permanent preparation of sclerites (1 slide), made available for future study.
Genetic data. GenBank NHM_027 COI-MF157500. Remarks. Forms a unique monophyletic clade distinct from other AB01 specimens (Fig. 27). No genetic matches on GenBank. Body shape and sclerites are characteristic for the family Pruvotinidae and indicative of the subfamily Lophomeniinae. Placement as sister to Hypomenia, another pruvotinid species, in the phylogenetic analysis (Fig.  27) confirms the family-level affiliation.
Ecology. Specimen collected from an epibenthic sledge tow across region of sediment and polymetallic nodules.

Discussion
Only one record of benthic mollusc taxa in the CCZ is hitherto reported on OBIS (OBIS 1017; iobis.org), with a further four just south of CCZ. In this study we report 42 records for 21 taxa, of which one is described as a new species. All our data and material from this study are made publicly available through this publication, and through depositing DNA extractions and tissue for further molecular analyses in the Molecular Collections Facility as well as morphological vouchers at the Natural History Museum in London, UK.
Mollusca is a diverse group with its members having very differing life histories, and in this study there are representatives of both sediment-dwelling species and nodule fauna. Not much is known about the mollusc species distribution and connectivity within the CCZ, an information deficit that makes it impossible to assess impact from anthropogenic activities. Genetic data is crucial for distribution analyses as some taxa look very similar and can be difficult to separate to species level based on morphology only, e.g. the new species Ledella knudseni and its sister taxon Ledella sp. (NHM_381). In our study we have used a precautionary approach when reporting taxa that are preliminary identified as described species with type locality far from CCZ, e.g. our Bentharca cf. asperula which is very similar to Bentharca asperula with type locality in Gulf of Mexico. Without genetic information from specimens collected at the type locality, we can not rule out that ours is a different species despite the similarity in morphology.
The protobranch bivalve Nucula profundorum is the most abundant bivalve mollusc in our samples, and population connectivity analyses are underway (Dahlgren et al. in prep). Morphologically it is identical to type material of the original Nucula profundorum, which was described from collections of HMS Challenger in the mid-North Pacific (36°N, 178°E) at about 3750 m depth (Fig. 10), and although our specimens were collected further south and east, the depth is almost the same. However, as we compare our sequences with published N. profundorum sequences on GenBank it is obvious that those two are different species. The sequences already published on GenBank come from specimens collected at about 1000 m depth off San Diego. Based on morphological similarity only, and the general observation that depth is a stronger barrier to dispersal than geographic distance (e.g Etter & Rex, 1990), our hypothesis is that our specimens are likely to correspond to N. profundorum and that the sequences attributed to N. profundorum on GenBank are erroneously identified.
There are very few DNA sequences from a few faunal groups from the CCZ available on GenBank, e.g. echinoderms (Glover et al. 2016b), cnidarians (Dahlgren et al. 2016) and polychaetes and crustaceans (Janssen et al. 2015). With our study including both morphological and molecular data we add greatly to our knowledge of genetic information in the CCZ and aim to improve the taxonomic understanding of benthic fauna in the CCZ to get a better picture of the distribution of taxa. These are essential data for the establishment of conservation strategies in the light of future mineral extraction. advice on Catillopecten. We would also like to acknowledge the expert support from the Senckenberg Institute team in the deployment and recovery of successful Brenke Epibenthic Sledge samples on the first ABYSSLINE cruise (Nils Brenke, Pedro Martinez Arbizu and Inga Mohrbeck). This study was made possible only by the dedicated help from the entire scientific party and the Masters and Crew of the Research Vessel Melville during the first cruise of the ABYSSLINE project in October 2013. Thanks also to Jackie Mackenzie-Dodds at the NHM Molecular Collection Facility, and Ben Scott of the NHM Diversity and Informatics group for work on the NHM Data Portal.