Myriotrochus hesperides O'Loughin & Manjon-Cabeza, sp. nov.

Myriotrochus hesperides O’Loughin & Manjón-Cabeza sp. nov.

Figure 2 e, f: table 1.

Material studied. Holotype. Antarctic Peninsula, BENTART–2006, R/V Hesperides, stn PA41, 65.47149ºS, 69.0285ºW, 350 m, 10 Feb 2006, MNCN 29.04/130; posterior dorsal body ossicles slide NMV F161516.

Diagnosis. Specimen 13 mm long; thin translucent body wall; sub-cylindrical, dorsal oral ring projecting anteriorly over ventral, body rounded distally; 12 peltato-digitate tentacles, each tentacle with about 7 small rounded digits; plates of calcareous ring asymmetrical, with short pointed anterior projections, wide rounded tongue-like posterior projections of variable length, 2 radial plates each with 2 anterior projections.

Tentacles lacking ossicles; body wall ossicles a few wheels only in the posterior dorsal body wall; wheels of one type, with teeth all pointing towards centre of hub; spokes irregular, about half branching proximally, some branches not reaching rim, some spokes with cross-connections; teeth variably sub-equal or different in size; hubs small, irregular, not disc-like, lacking perforations, formed by junction of spokes; largest wheel with diameter 248 µ m, hub diameter 40 µ m, 13 spokes at hub, 23 spokes at rim, 30 equal teeth; smallest wheel with diameter 200 µ m, hub diameter 24 µ m, 12 spokes at hub, 16 spokes at rim, 28 unequal teeth.

Colour (preserved). Off-white, translucent; tentacle digit ends reddish-brown.

Distribution. Antarctic Peninsula, 350 m.

Etymology. Named, as a noun in apposition, for the Spanish R/V Hesperides used for BENTART–2003 and BENTART–2006.

Remarks. Based on the key to the genera of family Myriotrochidae in Gage & Billett (1986), this new myriotrochid species is referred to Myriotrochus Steenstrup because it has: 12 tentacles; asymmetrical calcareous ring, with 2 radial plates each with 2 anterior projections; absence of rod ossicles; wheel hubs lacking perforations; wheel ossicles of one type only, with all teeth pointed towards centre of hub.

Three specimens of myriotrochid holothuroid have been taken in Antarctica. Smirnov and Bardsley (1997) described Myriotrochus antarcticus from a 2 mm long specimen from the MacRobertson Shelf in eastern Antarctica at 113 m. The wheels are 140–150 µ m in diameter, have 22–24 teeth, and 15–16 unbranched spokes, different to Myriotrochus hesperides O’Loughin & Manjón-Cabeza sp. nov. A New Zealand National Institute of Water and Atmospheric Research (NIWA) single specimen of a Myriotrochus species (registration NIWA 37812, two pieces, combined length 33 mm) was taken in the Ross Sea at 2283 m in 2008. The wheel diameters are 320–395 µ m, have about 30 teeth, have 11–15 unbranched spokes and a perforated spoked hub, also different to Myriotrochus hesperides O’Loughin & Manjón-Cabeza sp. nov. that is characterised by wheels with a small unperforated hub and frequently proximally branched spokes. The single type specimen is damaged, but appears to be intact, and has a complete oral end.

Myriotrochus hesperides O’Loughin & Manjón-Cabeza sp. nov. has some characters that are similar to Myriotrochus clarki Gage & Billett, 1986 from the Rockall Trough in the NE Atlantic at 1605–2515 m. Both species have large tongue-like posterior projections on the calcareous ring, but these are larger in M. hesperides and the anterior projections smaller. An “abnormal” wheel with a few distally branched spokes is illustrated for M. clarki, but all the M. hesperides wheels have numerous proximally branched spokes.