New sea cucumber species from the seamounts on the Southwest Indian Ocean Ridge (Echinodermata: Holothuroidea: Aspidochirotida, Elasipodida, Dendrochirotida) Author O’Loughlin, P. Mark Author Mackenzie, Melanie Author VandenSpiegel, Didier text Memoirs of Museum Victoria 2013 2013-12-10 70 37 50 https://museumsvictoria.com.au/collections-research/journals/memoirs-of-museum-victoria/volume-70-2013/pages-37-50/ journal article 10.24199/j.mmv.2013.70.04 1447-2554 12208349 DECF956F-C474-4C8D-82AF-48FD0EC0BB4A Amphigymnas staplesi O’Loughlin sp. nov. Zoobank LSID. http://zoobank.org/ urn:lsid:zoobank.org:act: 5CA0C7C6-BF6F-45E5-BE74-C36222E14F92 Figures 1 , 2 , 3 , 4 Material examined . Holotype . Southwest Indian Ocean Ridge, Atlantis Bank , 32.71ºS 57.28ºE , 707 m , JC066, event 8–3, parent no. 2605, specimen no. JC066–3666, ROV, 9 Dec 2011 , NHMUK 2013.4. Description . Body flat ventrally, domed to subrectangular elevation dorsally, 140 mm long, 30 mm wide midbody; mouth ventral, anus subdorsal posterior; body wall firm, thick, outer wall thin, calcareous, brittle; two paired, spaced single series of dorsolateral, conical papillae (four series across dorsally), each papilla up to about 7 mm long; pair of long dorsal posterior papillae up to about 12 mm long; two single series of larger ventrolateral conical papillae each up to about 15 mm long, about 18 papillae in each series; oral disc with ventral marginal continuous series of conical papillae, tapering in size from largest anteriorly to smallest posteriorly, total of about 30 papillae around oral disc; posterior to the oral disc a ventral transverse series of small conical papillae, irregular lengths; body with median ventral groove with single zigzag series of small tube feet on each side of groove, tube foot diameters about 0.6 mm, about 70 tube feet per series; irregular paired lateroventral series of larger tube feet, diameters about 0.8 mm, about 45 tube feet per lateral paired series; solid synallactid calcareous ring, lacking free-hanging tentacle ampullae; longitudinal muscles undivided; tuft of long thin gonad tubules with some basal branching, male; single polian vesicle; respiratory tree branches about a half body length. Dorsal body wall ossicles tables, discs with slightly lobed rounded margin, 160–240 µm across, disc with central cross, 4 large central perforations, up to 17 outer perforations, spires with 4 pillars, 2 cross-bars, pillars tapered to a point, lacking distal spines or teeth, spires up to 80 µm long. Dorsal and lateral papillae with irregular thick tables, discs up to 400 µm across, many outer perforations, high multiperforate spires, predominantly 4-pillared spires. Ventral body wall with mostly smaller thick 4-pillared tables, spires truncate, pillars lacking cross-bars, discs irregular, typically 160 µm across. Midventral tube feet endplates with very irregular branches creating perforations, diameters up to 520 µm; tube foot support rods straight to curved, widened midrod, irregular blunt marginal projections, rare perforations midrod and distally, rods up to 480 µm long; tube feet with very irregular tables. Tentacles with slightly curved rods, spinous on outer margin, about 480 µm long. Figure 1. RRS James Cook cruise map showing the Southwest Indian Ocean Ridge and the locations of the five seamounts that were visited during NERC JC066. The hydrothermal vent system studied during JC067 is indicated by the filled circle near Middle of What seamount. The sea cucumbers described in this study were collected from the Atlantis Bank , northeast on the Ridge,and the Coral Seamount,southwest on the Ridge. Figure 2. Photos of live holotype specimen of Amphigymnas staplesi O’Loughlin sp. nov. ( in situ on Atlantis Bank ; extracted from ROV video footage during cruise JC066; copyright AD Rogers University of Oxford/NERC; specimen NHMUK 2013.4). a, left ventrolateral view of rolling specimen with oral end right and left series of long, conical ventrolateral papillae prominent (up to 15 mm long); b, ventral view of rolling specimen with mouth right, ambulacral series of small tube feet evident, and left ventrolateral series of conical papillae again prominent. Colour. Live: body reddish-brown. Preserved: body brown, papillae off-white. Distribution . Southwest Indian Ocean, Atlantis Bank , 740 m . Etymology . Named for David Staples of the Marine Biology Section of Museum Victoria , in appreciation of his contribution during the JC066 voyage and his facilitation of the loan of these specimens to Museum Victoria that has made this work possible. Remarks . We refer our new species to Amphigymnas Walsh, 1891 on the bases of: brittle, calcareous outer body wall texture resulting from the presence of many large tables; long, conical, dorsal calcareous papillae, including a ventrolateral series; flat ventrum with small tube feet in ambulacral series. The three species currently assigned to Amphigymnas are distinguished by: dorsal tables have rare 3-pillared truncate spires, and ventral tube feet are in median series only ( A. bahamensis Deichmann, 1930 ); dorsal tables have rare truncate 4-pillared spires, and ventral tube feet are inconspicuous and scattered ( A. multipes Walsh, 1891 ); dorsal tables have predominantly complete 4-pillared spires, and ventral tube feet are in three discrete ambulacral series ( A. staplesi O’Loughlin sp. nov. ).