Benthic megafauna of the western Clarion-Clipperton Zone, Pacific Ocean Author Bribiesca-Contreras, Guadalupe https://orcid.org/0000-0001-8163-8724 Life Sciences Department, Natural History Museum, London, UK l.bribiesca-contreras@nhm.ac.uk Author Dahlgren, Thomas G. https://orcid.org/0000-0001-6854-2031 Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden & Norwegian Research Centre, NORCE, Bergen, Norway Author Amon, Diva J. SpeSeas, D'Abadie, Trinidad and Tobago Author Cairns, Stephen https://orcid.org/0000-0001-7209-9271 Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D. C., USA Author Drennan, Regan https://orcid.org/0000-0003-0137-5464 National Oceanography Centre, Southampton, UK Author Durden, Jennifer M. https://orcid.org/0000-0002-6529-9109 UMR ISYEB, Department Origines et Evolution, Museum national d'Histoire Naturelle, Paris, France Author Eleaume, Marc P. Collections & Research, Western Australia Museum, Perth, Australia Author Hosie, Andrew M. https://orcid.org/0000-0002-5683-662X Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia Author Kremenetskaia, Antonina https://orcid.org/0000-0001-8851-3318 School of Biological and Marine Sciences, University of Plymouth, Plymouth, UK Author McQuaid, Kirsty https://orcid.org/0000-0002-0395-8332 Museums Victoria, Melbourne, Australia Author O'Hara, Timothy D. Department of Oceanography, University of Hawai'i at Manoa, Honolulu, USA Author Rabone, Muriel https://orcid.org/0000-0002-8351-2313 National Oceanography Centre, Southampton, UK Author Simon-Lledo, Erik UMR ISYEB, Department Origines et Evolution, Museum national d'Histoire Naturelle, Paris, France Author Smith, Craig R. https://orcid.org/0000-0002-3976-0889 School of Life Sciences, University of Hawai'i at Manoa, Honolulu, USA Author Watling, Les https://orcid.org/0000-0002-6901-1168 School of Life Sciences, University of Hawai'i at Manoa, Honolulu, USA Author Wiklund, Helena https://orcid.org/0000-0002-8252-3504 Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden Author Glover, Adrian G. https://orcid.org/0000-0002-9489-074X National Oceanography Centre, Southampton, UK text ZooKeys 2022 2022-07-18 1113 1 110 http://dx.doi.org/10.3897/zookeys.1113.82172 journal article http://dx.doi.org/10.3897/zookeys.1113.82172 1313-2970-1113-1 EB46BF265F2E51B3A83799886C5F084A Laetmogone cf. wyvillethomsoni Theel , 1979 Fig. 49 Material. Clarion-Clipperton Zone • 1 specimen ; APEI 7; 4.8877°N , 141.7569°W ; 3132 m deep; 27 May. 2018 ; Smith & Durden leg.; GenBank : ON400689 (COI), ON406641 (18S); NHMUK 2021.18; Voucher code: CCZ_062 . Other material. Pacific Ocean • 1 specimen , holotype of Laetmogone spongiosa Theel , 1879; south of Japan ; 34. 1167°N , 138°E ; 1033 m deep; Challenger Expedition, Stn. 235; NHMUK 1883.6.18.47 . Description. Single specimen (Fig. 49A ). Body cylindrical, ~ 3 x as long as wide (L = 15.6 cm, W = 5.2 cm), with convex dorsal surface and somewhat flattened ventral surface, tapering posteriorly; mouth anterior, subventral, terminal; anus posterior, terminal, slightly dorsal; violet colouration in live and preserved specimen, with darker ventral surface (Fig. 49A-C ). Tentacles 15, of almost equal size, and very dark at the tips. Odd ambulacrum is naked; 27 or 28 tube feet arranged in a single row on each of the paired ventral ambulacra, forming a continuous line on the anterior ⅔ of the body and scattered posteriorly, also decreasing in size (Fig. 49C ). Each paired dorsal ambulacrum with a single row of long processes, 12 on the left and 13 on the right; longest processes longer than ⅓ of the body length. Twenty pedicels along each side of the ventral surface, posterior pairs smaller than the others. Fourteen processes of the bivium along the left ambulacra and thirteen along the right. Tegument is thick, completely covered by calcareous ossicles. Dorsal ossicles are wheel-like of various sizes (40-226 μm in diameter), with four or five studs, mostly five, on primary central crosses, and with 8-17 spokes, mostly eight on large wheels; ossicle is convex, rim smooth, interspoke areas small, and large central area on large wheels (Fig. 49D ). Figure 49. Laetmogone cf. wyvillethomsoni Theel , 1979. Specimen CCZ_062 A in situ image; B dorsal view of specimen before preservation C ventral view D dorsal calcareous ossicles. Scale bars: 2 cm ( A ); 1 cm ( B, C ); 50 μm ( D ). Image attribution: Durden and Smith ( A ); Wiklund, Durden, Drennan, and McQuaid ( B, C ); Bribiesca-Contreras ( D ). Remarks. Closest match on public databases for the COI gene sequence was other sequences of Laetmogone wyvillethomsoni Theel , 1879 (4.0-5.8% K2P genetic distance) from the Ross Sea and Marie Byrd Seamounts ( O'Loughlin et al. 2011 ). The specimen from the CCZ and specimens from L. wyvillethomsoni from Antarctica were recovered in our phylogeny (Fig. 34 ) in a well-supported clade (Fig. 34 ), which is subdivided in three clades including the two Antarctic clades stratified by depth reported in O'Loughlin et al. (2011) , and the specimen from the CCZ. Type material for L. wyvillethomsoni was collected during the H.M.S. Challenger expedition at stations 300 (off the coast of South America; 33.7° S, 78.3°W; 2514 m depth) and 147 (west of the Crozet Islands; 46.2667° S, 48.45° E; 2926 m), and high morphological variability was reported ( Theel 1879 ). The CCZ specimen morphologically resembles L. wyvillethomsoni , but no rod-shaped ossicles were found in the dorsal skin, differing from the original description. Ecology. The specimen was found on the sedimented seafloor of a seamount in APEI 7 at 3132 m depth. Comparison with image-based catalogue. No similar laetmogonid morphotypes have been encountered in seabed image surveys conducted in the eastern CCZ or in abyssal areas of the Kiribati EEZ. Consequently, the in situ image of specimen CCZ_062 was catalogued as a new morphotype (i.e., Laetmogone sp. indet., HOL_123). Class Ophiuroidea To date, there are 1201 records of ophiuroids occurring at> 3000 m depth in the CCZ, with 117 representing preserved specimens ( OBIS 2022 ). Four specimens belonging to three different species were collected and the barcoding gene COI was amplified for all but one, for which both 18S and 28S were amplified. These sequences, excluding 18S, were included in a concatenated alignment (28S, and COI) and used to estimate a phylogenetic tree (Fig. 50 ). Ophiuroidea is amongst the most challenging groups to identify and classify based on seabed image data only; key morphological features are too small to be appropriately visualised (e.g., plates and scales) and/or are found on the ventral disc (not visible in images). As a result, the taxonomic resolution of ophiuroid morphotypes catalogued from seabed imagery is usually much lower than that in other echinoderm groups. Consequently, connectivity and distribution patterns of ophiuroids derived from seabed image data should be interpreted cautiously. Figure 50. Phylogenetic tree of Ophiuroidea . Concatenated (28S, and COI) median consensus BEAST tree with posterior probability (PP) and bootstrap (BS) values indicated. Only values of PP> 0.70 and BS> 50 are shown, with values of PP> 0.95 and BS> 90 indicated with a circle. Nodes not recovered on the RAxML tree are indicated with a hyphen. Sequences generated in this study are highlighted in violet. Subclass Myophiuroidea Matsumoto, 1915 Infraclass Metophiurida Matsumoto, 1913 Superorder Ophintegrida O'Hara , Hugall, Thuy, Stoehr & Martynov, 2017 Order Ophioscolecida O'Hara , Hugall, Thuy, Stoehr & Martynov, 2017 Family Ophioscolecidae Luetken , 1869