Psolus atlantis O’Loughlin, 2013

O’Loughlin, P. Mark, Mackenzie, Melanie & VandenSpiegel, Didier, 2013, New sea cucumber species from the seamounts on the Southwest Indian Ocean Ridge (Echinodermata: Holothuroidea: Aspidochirotida, Elasipodida, Dendrochirotida), Memoirs of Museum Victoria 70, pp. 37-50 : 46

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).

Figures

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 theAtlantis Bank, northeast on the Ridge,and the Coral Seamount,southwest on the Ridge.

Figure 8. Photo of dorsal view of live holotype specimen of Psolus atlantis O’Loughlin sp. nov., attached to a rock fragment from Atlantis Bank collected during cruise JC066 (oral end left; specimen NHMUK 2013.6; photo taken by David Shale and used with permission).

Figure 9. Photos of holotype of Psolus atlantis O’Loughlin sp. nov. (preserved, 28 mm long, NHMUK 2013.6). a, dorsal view of holotype with oral valves left; b, dorsolateral view of holotype showing elevated oral valves; c, view of five triangular interradial oral valves and five narrow radial oral valves; d, ventral view of sole; e, ventral view of margin of sole showing inner series of large tube feet and outer series of small inconspicuous tube feet; f, view of sole showing scattered, small perforated plate and cross ossicles.

Figure 10. SEM images of ossicles from holotype of Psolus atlantis O’Loughlin sp. nov. (NHMUK 2013.6). a, tube foot endplate (top left; scale bar 100 µm) and tube foot support ossicles (scale bars 20 µm); b, small plates and crosses from central sole (scale bars 20 µm).