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 Psolus atlantis O’Loughlin sp. nov. Zoobank LSID. http://zoobank.org/ urn:lsid:zoobank.org:act: DE8353F7-D506-4264-8638-9FF3EA29254A Figures 1 , 8 , 9 , 10 Material examined . Holotype . Southwest Indian Ocean Ridge, Atlantis Bank , 32.72ºS 57.25ºE , 1117 m , JC066, event 8–5, parent no. 2547, specimen no. JC066–3686, ROV, 10 Dec 2011 , NHMUK 2013.6. Description . Body oval with slight posterior rounded taper, body 28 mm long, up to 17 mm wide, up to 7 mm high at oral cone; dorsal and lateral body covered by imbricating large multilayered scale ossicles of variable sizes, up to 7 mm wide, not perforated for tube feet, lateral marginal scales very small; dorsal and lateral scales sparsely but distinctly granular, granular appearance caused by pyramidal projections on the multilayered scale ossicles, not caused by small surface ossicles; oral cone dorsal with slight pyramidal elevation, 5 triangular interradial oral valves separated by 5 narrow radial oral scales, oral cone not discrete with dorsal scales encroaching basally on oral scales; anus dorsal posterior, surrounded by an irregular cluster of small scales. Distinct thin-walled sole, overhung marginally by small lateral scales; inner marginal, irregular, single to zigzag to double series of tube feet with diameters about 0.6 mm; outer marginal, single series of smaller inconspicuous tube feet with diameters about 0.3 mm; a few tube feet on midventral ambulacrum anteriorly and posteriorly, but lacking midventral series of tube feet. Ossicles in central sole small, thick, smooth crosses and plates with up to 7 perforations, ossicles up to 200 µm long; inner tube feet endplates with irregular small perforations centrally and irregular larger perforations marginally, margin smooth and not denticulate, endplate diameters up to about 400 µm; tube foot support ossicles irregular curved plates with more perforations than the ossicles in the sole, up to about 20, lengths up to about 200 µm long. Colour. Live: red dorsally. Preserved: white. Distribution . Southwest Indian Ocean, Atlantis Bank, 1117 m. Etymology . Named, in apposition, for the Atlantis Bank on the Southwest Indian Ocean Ridge from which this specimen was collected. Remarks . The morphological characters that distinguish, in combination, P. atlantis O’Loughlin sp. nov. from all other Psolus Oken, 1815 species are: five discrete triangular oral valves separated by single, thin rectangular oral plates; conspicuously granuliform oral, dorsal and lateral scales; absence of a midventral ambulacral series of tube feet; absence of any dorsal ossicles in addition to the large scales; small thick smooth perforated plate ossicles with fewer than eight perforations in the midsole; absence of cups or concave plate ossicles in the sole. We note the significant depth of occurrence ( 1117 m ) of P. atlantis , relative to the occurrence of most Psolus species. We have compared P. atlantis with other southern Psolus species directly or in the works of Carriol and Féral (1985) , Cherbonnier (1974) , Deichmann (1930) , Ekman (1925) , Ludwig and Heding (1935) , Mackenzie and Whitfield (2011) , O’Loughlin and Whitfield (2010) , Thandar (2009) , Théel (1886a , 1886b ) and Vaney (1906 , 1914 ).