Myriotrochus nikiae, O’Loughlin & VandenSpiegel, 2010

O’Loughlin, P. Mark & VandenSpiegel, Didier, 2010, A revision of Antarctic and some Indo-Pacific apodid sea cucumbers (Echinodermata: Holothuroidea: Apodida), Memoirs of Museum Victoria 67, pp. 61-95 : 69-71

Myriotrochus nikiae sp. nov.

Figure 5b ; table 2

Material examined. Holotype. Antarctica, Ross Sea , 71.23º S 174.44º E, 2281–2283 m, NZ IPY–CAML stn TAN0802/171, N. Davey, 26 Feb 2008, NIWA 37812 (in two parts).

Diagnosis. Myriotrochid species up to 33 mm long (2 parts combined); body wall thick, soft; 12 tentacles, withdrawn; lacking tentacle ossicles; calcareous ring comprising 10 plates; two dorsolateral radial plates each with 2 prominent tapering anterior projections, remaining plates with single prominent tapering anterior projection; posterior margin of calcareous ring slightly undulating, not concave; sac-like calcareous madreporite, dorsal, close to ring; single ventral polian vesicle; gonad comprises thick digitiform unbranched tubules arising in a series along gonoduct, 9 on one side of mesentery; ossicles in body wall myriotrochid wheels only, found throughout body wall; wheels of one type, all teeth pointing to centre of hub; hub large and disc-like, perforated, with regular circle of perforations separated by sometimes irregular hub spokes aligned with longer outer wheel spokes, some hub spokes branched distally; teeth blunt and rounded, of irregular length, generally longer over spokes than between spokes.

Measurements for 9 wheels: wheel ossicle diameters 320– 400 µ m, hub disc diameters 168–216 µ m, inner hub diameter 24–32 µ m, teeth length 48 µ m, spokes 11–15, teeth 22–36, spokes/teeth % 36–50, hub disc diameter/wheel diameter % 51–52, teeth length/wheel diameter % 12–15.

Colour (preserved). Body grey, not translucent; few small dark brown spots on tentacles.

Distribution. Eastern Antarctica, Ross Sea, 2283 m.

Etymology. Named for Niki Davey (NIWA), with appreciation of her generous and skilled collaborative assistance in determining Antarctic and New Zealand holothuroids.

Remarks. The specimen size, grey colour, form and size of the wheels, and form of the calcareous ring of Myriotrochus nikiae sp. nov. are similar to those of Myriotrochus bathybius H. L. Clark, 1920 from the eastern tropical Pacific Ocean (4º33'S 87º43'W, 3669 m), and according to Gage and Billett (1986) from the northeast Atlantic Ocean (Rockall Trough, 1800– 2925 m, and Porcupine Seabight, 3680–4310 m). Gage and Billett (1986) further judged Myriotrochus bathybius to be cosmopolitan at abyssal depths. Differences are such that we judge that the Antarctic specimen represents a related but different species.

For Myriotrochus bathybius, Clark (1920) gave three wheel diameters of 240, 300 and 340 µ m (size range smaller than for M. nikiae ), and two teeth counts of 37 and 38 (more numerous than for M. nikiae ). More significant for us is a wheel of M. bathybius that was illustrated in Clark 1920, and the teeth are uniform in length and distinctly pointed. Smirnov (1999, fig. 4) illustrated similar teeth for Myriotrochus (Oligotrochus) bathybius . The form of these teeth is in contrast with the irregular lengths of the quite rounded teeth of M. nikiae . Clark (1920) noted seven dark spots between tentacle bases. These are not present in the Antarctic specimen, but some dark spots are present on the tentacles.

For Myriotrochus bathybius, Gage and Billett (1986) reported a possible rough texture of the body wall in larger specimens (soft, thick body wall for M. nikiae ), and the calcareous ring clearly visible through the body wall (not visible through the thick body wall of M. nikiae ). Gage and Billett (1986) illustrated tapered teeth of uniform length with narrowly rounded points (in contrast with the bluntly rounded teeth of variable length for M. nikiae ).

As noted in the diagnosis the tentacles of the single specimen of Myriotrochus nikiae are withdrawn, and it was not possible to confidently describe them as “conical with lateral digits” or “peltato-digitate” as required for assignment to subgenus Oligotrochus M. Sars or subgenus Myriotrochus Steenstrup respectively (see Smirnov 1999).

Figures

Figure 5. a, montage photo of wheels from body wall of holotype of Myriotrochus hesperides O’Loughlin and Manjón-Cabeza, 2009 (Antarctic Peninsula; slide NMV F161516); b, montage photos of wheels from body wall of holotype of Myriotrochus nikiae sp. nov., with insert drawing of dorso-lateral radial (2 anterior projections) and adjacent inter-radial (single anterior projection) plates from calcareous ring (Ross Sea; NIWA 37812).