Biodiversity data and new species descriptions of polychaetes from offshore waters of the Falkland Islands, an area undergoing hydrocarbon exploration

Abstract Benthic environmental impact assessments and monitoring programs accompanying offshore hydrocarbon industry activities result in large collections of benthic organisms. Such collections offer great potential for systematics, biodiversity and biogeography research, but these opportunities are only rarely realised. In recent decades, the hydrocarbon industry has started exploration activities in offshore waters off the Falkland Islands. A large collection of ca. 25,000 polychaete (Annelida) specimens, representing some 233 morphological species was processed at the Natural History Museum, London. Taxonomic assessment led to recognition of many polychaete species that are new to science. The existing taxonomic literature for the region is outdated and many species in existing literature are likely misidentifications. Initially, an online taxonomic guide (http://falklands.myspecies.info) was created, to provide a single taxonomic source for 191 polychaete species to standardise identification across different environmental contractors working in Falkland Islands. Here, this effort is continued to make data available for 18,015 specimens through publication of raw biodiversity data, checklist with links to online taxonomic information and formal descriptions of five new species. New species were chosen across different families to highlight the taxonomic novelty of this area: Apistobranchus jasoni Neal & Paterson, sp. nov. (Apistobranchidae), Leitoscoloplos olei Neal & Paterson, sp. nov. (Orbiniidae), Prosphaerosyllis modinouae Neal & Paterson, sp. nov. (Syllidae) and Aphelochaeta falklandica Paterson & Neal, sp. nov., and Dodecaceria saeria Paterson & Neal, sp. nov. (both Cirratulidae). The potential of the Falkland Islands material to provide up to date informationfor known species described in the literature is also highlighted by publishing images and redescription of Harmothoe anderssoni Bergström, 1916 and Aphelochaeta longisetosa (Hartmann-Schröder, 1965). Biodiversity and abundance data are made available through a DarwinCore database, including material collected from 83 stations at Sea Lion developmental oil field in North Falklands Basin and voucher specimens’ data collected from exploratory oil wells in East Falklands Basin.


Introduction
Benthic Environmental Impact Assessments (BEIAs) generate large amount of data, which can provide a comprehensive characterisation of benthic habitats and associated fauna. However, several conditions need to be met for this potential to be realised. Most importantly the samples have to be collected in standardised way; the identification of organisms needs to be carried out in a consistent manner and the data should be made available in the public domain. Lack of this consistency can make data incomparable in a broader context and prevent iterative improvement of species identifications and concepts. While in well-known areas, such as North Sea this may be less of a problem, the case is magnified once the surveys move to previously unsampled regions and/or depths (see e.g., Brett 2001;Glover et al. 2015;Dahlgren et al. 2016). The current process used for samples collected as part of BEIAs from deep sea (areas below 200 m depth) is disjointed, with samples scattered across many different contractors and sub-contractors, and mostly lacking a standardised taxonomy. In recent decades, the potential for the development of a substantial offshore hydrocarbons industry within the Falkland Islands was realised (Blockley and Tierney 2017), with several benthic surveys carried out in 2008, 2009, 2011, and 2012. These surveys involved the identification and vouchering of large collections of benthic invertebrates from a poorly studied region of our planet. In this paper, we attempt to improve the data availability situation for offshore contracted work by making our species descriptions, raw data and vouchers available for future study as funded by the South Atlantic Environmental Research Institute (SAERI).
Marine benthic fauna from the Falklands area has been considered part of the Magellanic province, but links have also been drawn to the Southern Ocean and sub-Antarctic fauna (e.g., Arntz 1999). Available (and therefore used) taxonomic monographs of polychaetes for these regions (Hartmann-Schröder 1962Hartman 1966Hartman , 1967Hartman , 1978Hartmann-Schröder and Rosenfeldt 1988, 1989, 1990, 1992, however, need updating. Recent taxonomic efforts, which concentrated on the polychaete family Ampharetidae (Schüller and Jirkov 2013) summed up the problem as follows: "The Southern Ocean and also Patagonian waters represent an interesting geographical region, as many [polychaete] species recorded from these areas were originally described from the Northern hemisphere. These records from Southern waters may possibly be the result of misidentification and give some substance for the discovery of new species from already well-defined genera". For example, during ANDEEP (ANtarctic benthic DEEP-sea biodiversity: colonisation history and recent community patterns) expeditions to the deep Weddell Sea (Brandt et al. 2004) over 450 ampharetid specimens belonging to over 20 species (many undescribed) were found (Schüller et al. 2009;Schüller and Jirkov 2013). Similarly, recent BIOPEARL (Biodiversity, Phylogeny, Evolution and Adaptive Radiation of Life in Antarctica) expeditions to Scotia and, particularly, Amundsen Sea, revealed many species new to science for isopods, polychaetes, molluscs and tanaids (Kaiser et al. 2009;Neal et al. 2012Neal et al. , 2017Moreau et al. 2013;Pabis et al. 2015).
The problem of the lack of standardised taxonomy between contractors, highlighted in the "Gap Analysis" carried out by SAERI (Blockley and Tierney 2017), was one of the priority issues in developing an understanding of ecosystem functioning. A potential solution was found initially by developing an on-line taxonomic guide (http://falklands. myspecies.info) to provide a standardised taxonomic resource, particularly for those species that are currently not formally described. An abundant and species-rich benthic group, the polychaete worms, was selected as a model taxon to demonstrate the value of a taxonomic resource based on a large collection (ca.25,000 specimens), collected as part of the BEIAs by the contractors and subsequently identified at NHM, London. This paper is thus the first attempt at a partial, taxonomic synthesis for offshore waters of the Falkland Islands, based on currently available collections, and deals with description (formal or informal) of 191 polychaete taxa. Five new species from four families are formally described here to highlight the potential for discovery of species new to science in this material: Apistobranchus jasoni sp. nov. (Apistobranchidae), Leitoscoloplos olei sp. nov. (Orbiniidae), Prosphaerosyllis modinouae sp. nov. (Syllidae), Aphelochaeta falklandica sp. nov. and Dodecaceria saeria sp. nov. (both Cirratulidae). In addition, the material provides an opportunity to update and revise existing descriptions of known but poorly described or figured species. We illustrate this with two species -Harmothoe anderssoni Bergström, 1916 which is here redescribed and Aphelochaeta longisetosa (Hartmann-Schröder, 1965) where the holotype (ZMH-P15068) is imaged for the first time.
The availability of such data and collections to the research community is also an important part of the curatorial function of NHM London, therefore large number specimens (N = 18,015) were formally accessed into museum's collection (http://data.nhm.ac.uk/) following Darwin Core format and the data are made available here. The vouchering and curation of the specimens is of the utmost importance as specimens are the ultimate evidence as to what species have been found. This also creates an opportunity for more taxa to be formerly described as funding and interest develops in the region.

Falkland Islands
Falkland Islands are located in the south-western Atlantic, ca. 450 km north-east of Tierra del Fuego. The islands lie close to the edge of the Patagonian continental shelf and are considered to be part of the Magellan region (e.g., Hedgpeth 1969). From a geological point of view the Falklands Plateau and surrounding basins are result of the break-up of the Gondwana supercontinent in the Jurassic period. In terms of hydrography, there is a strong influence of Falklands Current which derives from the west wind drift around the Southern Ocean and an anticyclonic ring current that is formed around the Falkland Islands.

Field sampling protocol
Samples were collected during contractor-led environmental impact assessment surveys carried out in 2009, 2011, and 2012 ( Fig. 1). Two contractors were involved in the field sampling and sampling design (Fugro GB Marine Limited was responsible for 2009 survey and Gardline Limited for 2011 and 2012 survey), below is a summary of methodology used based on available field logs: 1. 2009 survey concentrated on four exploration wells: Toroa (ca. 600 m depth), Nimrod (ca. 1300 m depth), Loligo (ca. 1400 m depth) and Endeavour (ca. 1300 m depth). These wells are located in the East Falkland Basin, southeast to east off the Falkland Islands (see map in Fig. 1). In total 22 stations were successfully sampled, with up to two replicates collected at each station (see, DarwinCore file in Suppl. material 1 for details).
2. 2011 survey concentrated on four exploration wells: Hero (ca. 1800 m depth), Loligo (ca. 1300 m depth), Vinson (ca. 1500 m) and Inflexible (ca. 1800 m depth). These wells are located in East Falkland Basin, southeast to east off Falkland Islands (see map in Fig. 1). In total 18 stations were successfully sampled, with two replicates collected at each station (see Darwin Core file in Suppl. material 1 for details).
3. 2012 survey concentrated on the single exploration oil field -Sea Lion, at depths of ca. 450 m. Sea Lion field is located in North Falkland Basin, north of Falkland Islands (see map in Fig. 1). In total 83 stations were successfully sampled, with three replicates collected at each station (see DarwinCore in Suppl. materials 2, 3 for details). Most samples were collected using a USNEL box core (area 0.25 m 2 ), but in some cases Van Veen Grab sampler was deployed, where the use of boxcorer was prevented (see DarwinCore in Suppl. materials for details). The volume of sampled sediment was not always specified in the field logs and where specified, it varied considerably from 10 to 35 cm of top horizon removed and sieved. Additionally, subcores were taken in some instances for chemical and sedimentary analysis. All samples were sieved on a 0.5 mm mesh sieve. Specimens were fixed in 4% formalin and transferred into 70% ethanol for long-term storage.
Laboratory identification (carried out at NHM) Leica MZ6 and DM5000 stereo and compound microscopes were used to examine polychaete specimens. Images of these specimens were captured using a Zeiss V.20 and AxioCam HRc, and a Leica DFC 480 dedicated camera system connected to the DM5000. Photoshop software was used to edit photographs and to compile plates. A camera lucida system was used to draw the specimens. Helicon focus software (Heli-conSoft 2018) was used to create composite images of specimens taken at different focal points. The software combines such images to create a clear and focused final image. Specimens of Harmothoe anderssoni and Proshpaerosyllis modinouae sp. nov. were also examined using a FEI QANTA FEG 650 (FEI, USA) SEM. These specimens were first dehydrated to 100% alcohol before being critically point dried, mounted on stubs, and coated with gold-vanadium using a sputter coater.

Species determinations
From the material examined, in total 233 species were determined following morphological examinations during the contract work, with 191 species included in on-line taxonomic guide (see the checklist). Of these, 123 species were determined from exploration wells in the East Falklands Basin and 110 species from the Sea Lion exploration field in the North Falklands Basin. Voucher specimens, the bestpreserved representatives of each taxon, were selected to represent each morphospecies found in the material. Vouchers were not necessarily in "pristine condition", and not all characters were always observed or determined with certainty. Thus, polychaete morphospecies determined fall into three groups: 1. "The Knowns" -these are species known to science and described from "the region" (Magellanic province, sub-Antarctic islands and parts the Southern Ocean, deep-parts of the Atlantic or Pacific Oceans were also sometimes considered). These species were assigned to known Linnean-named species (e.g., Onuphis pseudoiridescens Averincev, 1972). "The Knowns" represent a small group of the available Falkland Islands polychaete fauna, with 37 species, representing only 16% of our total (available) material.
2. "The Uncertain" -the status of such species is currently uncertain and these are designated "cf." The reasons of uncertainty were usually as follows: i) specimens were too damaged and/or incomplete, therefore not all characters could be observed; ii) species were considered cosmopolitan having a wide geographic and/or bathymetric distribution, with the type locality outside of "the region" as defined earlier (usually the type locality is in Northern Europe); and/or iii) the original description is of little value (too short, too general, based on incomplete or damaged specimens, unaccompanied by drawings etc.). The type specimens housed at NHM collection were always examined, but those housed by other institutions were not always requested due to time constraints of the initial phase of this project and should be examined in the future work. Only 30 species were assigned to this category, ca. 13% of the diversity.
3. "The Unknowns" (new species) -includes species which were recognised as new to science and ca. 70% of species fall into this category. These taxa are currently assigned to morphospecies name (e.g., Leitoscoloplos sp. 1) and some will be formally described. However, many of these species are represented by only one specimen and/or the specimens are damaged or too incomplete to provide a full diagnosis. It is hoped that future sampling work will provide better examples of such species, enabling their formal description.
An on-line taxonomic guide was created for 191 morphospecies using the Scratchpad platform (Smith et al. 2012) and links to preliminary informal descriptions and images can be found in the check list in this publication. The taxonomic guide itself is an identification tool and its aim is not solving taxonomic problems. These are merely highlighted (where possible), stressing the need for future work by taxonomic experts in particular polychaete groups. Finally, it is important to note, that only morphological examination has been carried out so far as the specimens were not suitable for molecular work. Ultimately, recent taxonomic research has shown that morphological examination has its limits and molecular work is often needed to resolve taxonomic problems (Nygren 2014).
The remainder of this publication concentrates on re-descriptions or formal descriptions of new species, where material was available in condition that is conductive to observation of important taxonomic characters. Whilst this work concentrates on a fraction of the 'unknowns', it represents a useful advance, coupled with the significant effort to make raw data and vouchers for the entire collection available for loan. Many known species described in the late 19 th and early 20 th centuries suffer from poor descriptions and lack of images. Thus, we provide an up to date description, accompanied by photographs and SEM images for Harmothoe anderssoni Bergström, 1916 a commonly reported species from the area, with confused taxonomic history to highlight the potential of material presented in this publication. Similarly, Hartmann-Schröder (1965) described Aphelochaeta longisetosa but did not provide any figures. We have taken the opportunity to provide images of the holotype as well as specimens of the species collected from the Falkland Islands.

Accession of the specimens into NHM London collection
Voucher specimens (N = 161) from East Falkland Basin surveys were formally accessioned into museum's collection and the data are here made available via Darwin Core Database (Suppl. material 1). We also undertook accession-ready re-sorting of the material from the North Falkland Basin (Sea Lion oil field). As a result, 15,394 specimens were accessioned at species level (Suppl. material 3) and 2,460 specimens were accessioned at family level (Suppl. material 2) due to time constraints on the re-sorting. All together 18,015 specimens were accessioned to date out of total of ca. 25,000 specimens available.
Remarks. During preliminary assessment of Falkland Islands specimens these were assigned to Harmothoe due to presence of bidentate neurochaetae, as well as other generic characters such short body, 15 segments with elytra, prostomium with cephalic peaks and neuropodia with supra-acicular lobes. However, this species did not match any described or recently reviewed species of Harmothoe from the Southern and South Atlantic Oceans (Barnich et al. 2006;Barnich and Fiege 2009;Barnich and Fiege 2010;Barnich et al. 2012;Miranda and Brasil 2014). The form of elytra was, however, consistent with that described for Eunoe anderssoni, a Southern Ocean species, which has a confused taxonomic history. It was originally placed in genus Harmothoe by Bergström (1916), referred to as Eunoe by Monro (1936), moved to Hermadion by Fauvel (1950) and again considered Eunoe by Hartman (1966). Our understanding is that the reports of Polynoe hirsuta from Chile by  are misidentified specimens of H. anderssoni, given they were recognised as such by Bergström (1916) and Fauvel (1950). Given that Ehlers' specimens are not available for examination we prefer not to include these in formal synonymy.
The genera Eunoe and Hermadion share some characters with Harmothoe such as a short body and the presence of 15 elytragerous segments (see e.g., Barnich and Fiege 2009Bock et al. 2010), but while prostomial cephalic peaks and neuropodial supracicular lobes are present in Harmothoe and Eunoe, these are lacking in Hermadion (see Barnich and Fiege 2006). However, Eunoe supposed to have only unidentate neurochaetae (see e.g., Fiege 2009, 2010), while supra-acicular neurochaetae in Falkland Island specimens are clearly bidentate. Unfortunately, Bergström (1916) did not comment on the form of neurochaetae in detail, but subsequently both unidentate and bidentate neurochaetae were reported in Eunoe anderssoni by Monro (1936), Hartman (1953) and Hartmann-Schröder and Rosenfeldt (1992). Monro (1936) commented that three out of six specimens had unidentate chaetae only, but in our experience, the slender secondary tooth becomes easily abraded, which may erroneously lead to the conclusion that all neurochaetae are unidentate. The original placement of this species in genus Harmothoe is therefore justified and is referred to here as Harmothoe anderssoni. It is important to stress that this decision is driven by practical ease of identification rather than phylogenetic position of this species. Recent molecular work on Polynoidae suggests paraphyly of Harmothoe (e.g., Norlinder et al. 2012) and the current designation of polynoid genera is likely problematic. Here, we do not attempt to solve systematic difficulties, but provide new information on Harmothoe anderssoni with photographs, high quality SEM images (see also Hartmann-Schröder and Rosenfeldt 1992) and detailed description of this species based on material from Falkland Islands.
Palps very short, almost entirely obscured by prostomium in dorsal view (Figs 5b, c; 7a-d; 8a) with only their lateral margins visible in dorsal view; fully fused along their length; provided with some small papillae (Fig. 8b). Two pairs  of large red eyes present (Figs 5b-d; 8a), in trapezoid arrangement, with anterior and posterior pair close together (almost appearing as a single eye), anterior pair cup-shaped, posterior pair circular; presence of additional eyespots not confirmed.
Remarks. Falkland Island specimens were assigned to genus Prosphaerosyllis San Martín, 1984 based on morphological characters only as no reproductive specimens were observed. San Martín (2005) emended the generic diagnosis and further distinguished Prosphaerosyllis from the similar genus Sphaerosyllis, however here we provide a comparison for species in both genera with the type locality in the southern waters because not all species have been revised. Sphaerosyllis antarctica, S. hirsuta, S. sublaevis, S. capensis, S. dubiosa, S. lateropapillata uteae and Prosphaerosyllis kerguelensis (holotype BMNH.85.12.1.155 examined as part of this study) can be easily distinguished from the Falkland Island species due to absence of dorsal cirrus on chaetiger 2. Of species with a dorsal cirrus on chaetiger 2 present (S. semiveruccosa, P. joinvillensis, P. capensis chilensis, S. brandhorsti and P. brachycephala) the new species can be easily distinguished by having small antennae and short palps (often with only their lateral margins observable in dorsal view, otherwise mostly obscured by prostomium).
Falkland Islands species is most similar to P. isabellae De Nogueira, San Martín & Amaral, 2001 described from intertidal depths in Brazil in having short antennae and a sparse distribution of body papillae. However, other than length of the palps, P. modinouae sp. nov. can be further differentiated by having all falcigerous blades serrated (these are smooth from mid-body chaetigers in P. isabellae), in lacking iridescent inclusions in the dorsal cirri and in the dorsal cirri becoming elongated throughout the body in P. modinouae sp. nov. There also appear to be greater differences in length of falcigerous blades in P. modinouae sp. nov. (Fig. 10d-g) compared to P. isabellae (see DeNogueira et al. 2001;Fukuda et al. 2009). We also suggest that Brazilian specimens from bathyal depths assigned to P. isabellae by Fukuda et al. (2009) may in fact represent a different species, even more closely aligned to P. modinouae sp. nov. This suggestion is based mainly on much deeper distribution (down to 650 m) reported by Fukuda et al. (2009) compared to 4-7 m depth at the type locality of P. isabellae, which was also reported to be associated with coral colonies (De Nogueira et al. 2001). However, specimens of P. isabellae were not available for examination as part of this study.
Another similar species is Sphaerosyllis palpopapillata Hartmann-Schröder & Rosenfeldt, 1992 described from the Antarctic Peninsula, 300 m depth. Unfortunately, the description and drawings provided by Hartmann-Schröder and Rosenfeldt (1992) are of limited value. Therefore, the holotype (ZMH P-20751) was loaned from Zoologisches Museum Hamburg and photographed here for the first time (Figs 11a; 12a-f ). The holotype, which is the only known specimen of this species, was found to be a small anterior fragment, with structures such as the antennae now missing and some chaetae broken off. As a result, S. palpopapillata remains a poorly known species, until new material from the type locality becomes available. The holotype (ZMH P-20751) (Fig. 11a) is similar to P. modinouae sp. nov. (Fig. 11b, c) in the form of the palps and also possesses the elongated lateral body papillae (Fig. 12d), which were not reported by Hartmann-Schröder and Rosenfeldt (1992), although the rows of dorsal papillae were not confirmed by us. The main differences observed were the form and length of ventral cirri, which are distinctly longer and slender in S. modinouae sp. nov. (Figs 9b,c;12b,c). While both species have unidentate falcigers, their blades in S. palpopapillata are shorter (6-7 µm) and similar in size where observed (Fig. 12e, f ), but in the new species their lengths are more variable (Fig. 10d-g) as already discussed in comparison with P. isabellae. Furthermore, the image provided in the original description (Hartmann-Schröder and Rosenfeldt 1992: fig. 34) suggests that antennae in S. palpopapillata are large, not small as in the new species or in P. isabellae. Unfortunately, as already mentioned, the antennae have since been lost in the holotype of S. palpopapillata and this character cannot be verified.
The lack of detailed descriptions and reliable drawings/images of the known species from the southern waters, complicate the efforts in describing new species. While we believe that observations provided in this study justify the establishment of a new species from the Falkland Islands material, the known species are clearly in need of revision. However, such an undertaking is beyond the scope of this study.
Etymology. This species is dedicated to Yvett Modinou, a passionate science communicator, who inspired the fourth author (BS) to join the NHM London.
Distribution. This species is only known from its type locality, North Falklands Basin, ca. 450 m depth.
Methyl Green stain pattern (Fig. 13c). Stain retained on prostomium and peristomium, chaetigers 1-4 do not retain stain (pale stain at the best), chaetigers 5-10 stain lightly interramally, from chaetiger 12 until end of the fragment with stain strongly concentrating on the posterior edge of the neuropodial lamellae, but no patterns of dorsum or ventral surfaces observed.
Remarks. New species belongs to an Apistobranchus group in which notopodia are missing on chaetigers 1 and 7-10, with neuropodium on chaetiger 4 multilobed (see Blake 1996). The Falkland Islands species is clearly different from Apistobranchus glacierae Hartman, 1978 the only valid species known from the area according to Petti et al. (2007), who clarified the status of A. glacierae and A. gudrunae Hartmann-Schröder & Rosenfeldt, 1988. In A. glacierae the notopodia are absent on chaetigers 1 and 8 only, unlike A. jasoni sp. nov. in which they are absent from chaetigers 1 and 7-10.
It is difficult to distinguish Falkland Islands specimens from A. ornatus Hartman, 1965 redescribed by Blake (1996) from the Pacific, which in turn is difficult to distinguish from A. typicus (NW Atlantic distribution) other than by methyl green stain (see discussion in Blake (1996)). Falkland Island specimens do not stain uniformly as Blake (1996) reported for A. ornatus and no paired ventral line extending from chaetiger 7-8 has been detected. Stain is, however, more pronounced in Falkland Islands specimens then in A. typicus, in which a pale reaction is limited to swollen dorsal glandular areas according to Blake (1996). Further, while the posterior protruding spine has been reported in A. ornatus (Blake & Petti, 2019), to our knowledge there has been no reports of its accompanying capillary as observed in Falklands specimens (Fig. 15b). Additionally, when comparing specimens with similar number of segments, further subtle differences can be detected and these are summarised in Table 1. Overall, the Falkland Island specimens are smaller and more slender than A. typicus and A. ornatus, with fewer rows of neurochaetae and fewer lobes on chaetigers 4. We suggest that there is evidence that Falkland Islands' specimens represent new species.
Etymology. Species name is dedicated to Jason Huque, husband of the sixth author (CH). Co-incidentally, Jason Islands are also an archipelago in the Falkland Islands.
Distribution. This species is known only from its type locality, North Falklands Basin, at ca. 450 m depth.  Blake (1996) and A. typicus as reported by Webster and Benedict E (1887).

Variation in A. jasoni
sp. nov.
Remarks. Currently, twelve species of Leitoscoloplos are known from the Magellanic province and the Southern Ocean (see Table 2) thanks to revisionary work of Mackie (1987) and more recently Blake (2017). The genus Leitoscoloplos became species rich in the southern waters, as previous reports of L. kerguelensis (Fig. 19b) were re-examined.
Leitoscoloplos olei sp. nov. is very similar to L. platensis Blake, 2017 recorded off Uruguay and Argentina, in the intertidal to 144 m depths in coarse sediments. Both species are small and slender, sharing similar form of prostomium, thoracic Table 2. Comparison of Leitoscoloplos olei sp. nov. with species known from the region based on literature (Mackie 1987, Blake 2017). An asterisk indicates that only the diagnosis given by Mackie (1987) is considered valid here. and abdominal postchaetal lobes (both noto-and neuropodial) and having asymmetrical branchiae, which Blake (2017) describes as having lateral lobe. The main difference is the start of branchiae, which is in chaetigers 13-16 in L. platensis, but 17-18 (mostly 18) in L. olei sp. nov. from Falkland Islands. Additional differences are more subtle. Blake (2017) commented that furcate chaetae are only rarely found in L. platensis, but these are commonly encountered in abdominal notopodia of L. olei sp. nov., numbering two per fascicle. The two species also differ in bathymetric distribution, which is shallower in L. platensis (intertidal to 144 m), but deeper in L. olei sp. nov. (ca. 450 m).
For full comparison of Leitoscoloplos species known from the area see Table 2, as well as discussion in Mackie (1987) and Blake (2017).
Etymology. Specific name olei is genitive case of oleum, which is Latin for oil, to acknowledge the discovery of this species during the oil exploration activities.
Distribution. This species is only known from its type locality, North Falklands Basin, at ca. 450 m depth.
Chaetae positioned laterally in thoracic segments but becoming more ventral in subsequent segments. Thoracic chaetae relatively long thin capillaries; notochaetae of two sizes, long capillaries of approximately up to ten chaetigers in length, giving specimens a 'hairy' appearance, long chaetae appear from anterior thoracic chaetigers and occur down body, only becoming shorter in distal part of abdomen, shorter capillaries less than six chaetigers long also present; thoracic neurochaetae slightly shorter. Pygidial segments widening before narrowing and tapering towards anus, distinct ventral groove observed, terminal anus with low lobes, ventral lobe large extending with an acute tip (Fig. 20c).
Methyl Green stain pattern. Holotype without any discernible pattern. Remarks. Aphelochaeta longisetosa has been only recently redescribed by Blake (2018) based on re-examination of holotype and additional material from off Ecuador and Chile. However, as the holotype was never illustrated, we take the opportunity to further update the description of this species by providing images of the holotype (Fig. 20). Few minor differences have been detected between re-description provided here and that of Blake (2018) regarding the position of dorsal tentacles and first pair of branchiae. While Blake (2018) considered these structures to be associated with chaetiger 1, here we observed the dorsal tentacles on distal edge of peristomium and first chaetiger, dorsal and proximal to first branchia. Table 3 gives a comparison of Aphelochaeta species that might be found in the Falkland Islands region. Description. Specimen 16 MFC anterior fragment 16.3mm long with 79 chaetigers, specimen 60 MFA 11mm long with 67 chaetigers. Body widening gradually in thorax region, dorsally hump-backed, thoracic chaetigers crowded, narrow, wider than long, becoming longer and more flaccid in abdominal chaetigers; ventrally, groove present from mid thorax down the body (Fig. 21b).
Prostomium conical, bluntly pointed. Peristomium wider than long, domed dorsal crest over first two annulations of peristomium, three annulations seen laterally and horizontally (Fig. 21a, c). Dorsal tentacles separated, situated laterally on distal edge of peristomium and first chaetiger, dorsal and proximal to first branchi- ae (Fig. 21c). Following branchiae situated dorsal to notochaetae separated by at least one branchial diameter from dorsalmost notochaetae.
Chaetae positioned laterally in thoracic segments. Thoracic notochaetae of two sizes, long capillaries approximately up to 10 chaetigers long, giving specimens a 'silky' appearance, long chaetae similar in length perhaps slightly longer in distalmost thoracic chaetigers; thoracic neurochaetae slightly shorter; 7-10 notochaetae and 6-8 neurochaetae per fascicle. Abdominal notochaetae fewer in number than neurochaetae and less dense than in thoracic chaetigers; a few long chaetae appear from anterior thoracic chaetigers and occur down body into the abdominal chaetigers, shorter capillaries less than six chaetigers in length also present.
Pygidial region expanded, pygidium with lobes the ventralmost enlarged and pointed (Figs 21d; 24a) Methyl Green stain pattern. Falkland Islands specimens with band or spot on ventral prostomial region extending into mouth, diffuse staining on sides of peristomium, distinct partial bands ventrally on thoracic chaetigers along edges of the chaetigers, becoming denser in mid and proximal thoracic chaetigers, some banding dorsally on thoracic chaetigers (Fig. 22).
Remarks. Aphelochaeta cf. longisetosa (Hartmann-Schröder, 1965) was identified from a number of samples during the contract, but only a few specimens have so far been registered in the Museum's collection. The Falkland Islands specimens closely resemble Hartmann-Schröder's holotype, particularly in possessing the long silky chaetae (see Table 3). The Falkland Islands specimens differ in the shape of the body; they show a distinct staining pattern which is absent in A. longisetosa; however, this might be due to difference in the age of the specimens, and the abdominal notochaetae are fewer in number than neurochaetae and less dense than in thoracic chaetigers. Given these observations and that the Falkland Islands lie outside the previous range of A. longisetosa we are taking a cautious position and assigning the specimens to A. cf. longisetosa.
Aphelochaeta cf. longisetosa resembles A. falklandica sp. nov. having similar MGSP but differs in the shape of the body, A. cf. longisetosa has a near cylindrical body with only a slight widening in the proximal thoracic region and with no obvious junction between the thorax and abdomen, whereas in A. falklandica sp. nov. the thorax is flat with the body widening in the thoracic region and narrowing again at the junction between the thorax and abdomen; finally, the pygidium has an extended lobe with a pointed tip, whereas A. falklandica sp. nov. has a rounded ventral lobe. Such differences appear to be consistent and so it has been decided to consider them as separate species.
In terms of other known Aphelochaeta species in the region, A. cf. longisetosa resembles A. malefica Elias & Rivero, 2009, in the body shape as the species from the River Plate has a body more uniform in width. However, the two species differ in that the peristomium is much shorter in the Falkland Islands specimens, only as long as wide, whereas in A. malefica Elias & Rivero, 2009 the peristomium is longer than wide in the position of the dorsal tentacles and first branchiae and that the latter also has the peristomium extending back displacing the first chaetiger, while A. cf. longisetosa the junction is not displaced proximally. The MGSP for the two species is also different. The Falkland Islands species have only diffuse staining in the peristomium and prostomium while A. malefica has these areas darkly stained.

Aphelochaeta falklandica
Prostomium wide, conical with rounded or 'stumpy' point. Peristomium as wide as long, with domed dorsal crest; three annulations, first two obvious in lateral and ventral view, interrupted by dorsal crest, third complete dorsally and extending distally into first chaetiger. Dorsal tentacles arising between peristomium and first chaetiger, sometimes appearing to arise in the first chaetiger due to the peristomium extending back into the first chaetiger; dorsal to and on the same level or slightly anterior to first branchiae; second branchial pair close to first pair (Figs 23e; 24e).
Chaetae all simple capillaries, thoracic notochaetae of two basic lengths-relatively short capillaries ca. four chaetigers in length or equivalent to half the chaetiger width, and longer chaetae of at least ten chaetigers length; long chaetae arising from posterior thoracic region occurring in subsequent chaetigers into abdominal region; 6-10 chaetae per fascicle sometime appearing as if in two groups. Thoracic neurochaetae short capillaries, similar in length as short capillaries in the notopodia; 5-6 chaetae per fascicle. Abdominal notochaetae longer than those of neuropodia, smaller numbers of chaetae in abdominal fascicles than in thorax.
Methyl Green stain pattern. Band ventral under the prostomium extending into the mouth, narrow bands along lateral and ventral edges of thoracic chaetigers (Fig. 23).
Remarks. Aphelochaeta falklandica sp. nov. is a common species in the Sealion samples. It closely resembles A. cf. longisetosa (Hartmann-Schröder 1965), differing in being more dorso-ventrally flattened with an obvious widening of the body in the thoracic region, with an obvious junction between the thoracic and abdominal chaetigers and in the blunt shape of the ventral anal lobe (see Figs 23f; 24c). In mixed samples this species can often be distinguished by a full gut obvious in posterior thoracic and anterior abdominal chaetigers and, in fresh material, by the bases of branchiae in the posterior thorax showing as bright red dots. The domed dorsal crest is also characteristic.
Aphelochaeta falklandica sp. nov. closely resembles A. palmeri Blake, 2018 and A. spectabilis Blake, 2018 both recently described from Antarctic and South American waters; A. falklandica sp. nov. has a similar body shape to these species but appears to differ in the following ways: the definition of the annulation differs slightly in that with A. spectabilis the junctions of the annulations are only weakly defined whereas in A. falklandica sp. nov. the junctions of the annulations are distinct although can be less easy to see dorsally if the dorsal crest is well developed. The dorsal tentacles of A. spectabilis arise on the posterior part of the peristomium or in the junction between the peristomium and first chaetiger, with the first branchia arising on the first chaetiger. In A. falklandica sp. nov. the dorsal tentacle also arises in the junction between the first chaetiger and peristomium but the first branchia arises ventral to the dorsal tentacle and in the junction between the first chaetiger and the peristomium. Aphelochaeta falklandica sp. nov. has a ventral groove running from the mid to posterior thoracic region of the body. Aphelochaeta spectabilis does not have a ventral groove. In A. spectabilis the development and shape of the posterior chaetigers and pygidial region is fusiform and well developed with a simple pygidium with a rounded lobe, whereas in A. falklandica sp. nov. this region is not as fusiform and the pygidium has an extended blunt ventral lobe. The staining pattern for A. spectabilis differs from A. falklandica, being more developed occurring dorsally on the peristomium, there is a distinct patch posterior of the mouth and the first chaetiger. These patches are missing from A. falklandica sp. nov., but this species has patches on the lateral parts of the peristomium, there is a small band ventrally on the prostomium.
The shape of the prostomium in A. palmeri is pear-shaped, slightly indented at its junction with the peristomium; the prostomium in A. falklandica sp. nov. is conical and with a blunt rounded tip. The dorsal crest in A. falklandica is not always well developed and may extend only as far as the second annulation whereas the dorsal crest in A. palmeri is usually well developed extending to the end of the peristomium. Aphelochaeta palmeri has a well-developed posterior region with a fusiform shape and a blunt lobed pygidium. In A. falklandica sp. nov. this region is not so well developed and expanded. The staining pattern differs in that there are distinct bands ventrally in the prostomium and a large patch laterally on each side of the peristomium in A. falklandica sp. nov. which are absent in A. palmeri.
Aphelochaeta falklandica sp. nov. can be distinguished from the A. malefica Elias & Rivero, 2009 by the arrangement of the dorsal tentacles, third annulation of the peristomium and MGSP. The shape of the body suggests similarities with A. williamsae Blake, 1996 from California but A. falklandica sp. nov. differs in MGSP which have banding extending laterally while in A. williamsae they do not. Aphelochaeta falklandica sp. nov. differs from the other Californian species in that the dorsal thorax is flattened and ventrally more rounded, whereas most of Blake's (1996) species are dorsal-ventrally rounded or have a rounded (humpbacked) dorsal thoracic shape. Table 3 gives the comparison of Aphelochaeta species that might be found in the Falkland Islands region.
Etymology. This species is named after the Falkland Islands where it was discovered.
No achaetous segment, chaetigerous segments start after peristomium. Anterior chaetigers with simple capillaries, five in notopodia and four in neuropodia. Spines beginning on chaetiger 22-29; podia with mix of capillaries and spines, up to six spines and four to five capillaries, becoming 8-13 spines in fascicules of distal chaetigers. Spines with excavated tips, smooth edges. Chaetigers of pygidial area with only capillaries.
Remarks. Seven species of Dodecaceria have been recorded in the region (see Table 4 and Fig. 27). Three species also have two or three pairs of branchiae: D. gallardoi Carrasco, 1977bfrom Chile, D. laddi Hartman, 1954 from the Marshall Islands, and D. laddi oculata Hartmann-Schröder, 1962 from Peru. Dodecaceria saeria sp. nov. appears to differ from these species in the shape of the spoon-like spines (Fig. 22) and in the position where these spines first arise, chaetiger 22 to 29 as compared with much earlier in the three other species.
Etymology. This species is named after the South Atlantic Environmental Research institute (SAERI) which has done so much to support the taxonomic work included in this paper.
Distribution. This species has only been recorded from the Falkland Islands. Dodecaceria species are more commonly associated with rock or shell burrowers. The log of the cruise states "Mostly black gravel up to 1.5cm diameter in sieve residue" which may account for the occurrence of this taxon in predominately soft sediment.  geodata conversions and Ilaria Marengo also provided the map in Figure 1. Our thanks also to Dr. Martin Schwentner and Kathrin Philipps, Universität Hamburg -Zoologisches Museum for the loan of specimens.