Parathyonidium incertum Heding

Parathyonidium incertum Heding

Figure 1 d–f; table 1.

Parathyonidium incertum Heding (in Heding & Panning, 1954): 37–39, fig. 3.

Material examined. Antarctic Peninsula, Low I., BENTART–2006, R/V Hesperides, stn LOW47, 63.4668ºS, 62.2151ºW, 115 m, 12 Feb 2006, MNCN 29.04/126 (1 specimen), body wall ossicles slide NMV F161525; MNCN 29.04/127 (2 specimens), posterior body ossicles slide F161526, tentacle ossicles slide F161527; South Atlantic Ocean, South Georgia, Icefish 2004, stn 47 BT 25, 114–118 m, 12 Jun 2004, NMV F104998 (1).

Diagnosis. Specimens up to 35 mm long (tentacles partly extended, preserved, NMV F104998), subcylindrical, elongate, widest diameter 5 mm; soft thick non-calcareous body wall; lacking distinct sole ventrally; oral end sometimes upright, slightly tapered and rounded distally when tentacles withdrawn; anal end slightly tapered and rounded distally; 15 dendritic tentacles (variable; “ type ” has 13; F104998 has 16), unequal, some undeveloped (buds only); long digitiform genital papilla posterior to dorsal tentacle pair in male specimen (indicative of internal fertilization and brood protection); tube feet confined to radii, spaced single series of large tube feet, uniform in size from base of tentacles to anus; calcareous ring faintly evident, only radial plates evident, wide anteriorly and posteriorly, narrowed in mid-plate, 2 small notches anteriorly, deep rounded notch posteriorly.

Ossicles in body wall abundant, thin, bluntly spinous to smooth, single-layered irregular plates, few to many perforations; similar dorsally and ventrally; common form elongate, with 2 large central perforations, 2 small distal perforations, one extended end with few small perforations, short blunt spines on surface and around margin, typically 100 µ m long; small plates intergrade with larger smooth to knobbed, marginally denticulate plates, up to 200 µ m long. Tube foot endplates large, up to 360 µ m diameter, few perforated support plates, not rods. Tentacles ossicles perforated plates, not rods, round to oval, slightly concave, blunt marginal denticulations, some with central knob, some fine surface knobs, plates up to 200 µ m long.

Colour. Live: semi-translucent pale brown. Preserved: pale grey.

Distribution. South Georgia, Antarctic Peninsula (Low I.), 114– 199 m.

Remarks. In Heding & Panning (1954, p. 37) Panning notes that Heding died before their MS was completed, and before Heding was able to work on a Discovery Report. Panning wrote that he erected the new genus Parathyonidium Heding, 1954 and new species Parathyonidium incertum Heding, 1954 based on the notes by Heding, and with the approval of Dr. Deichmann (Harvard University). The specimens (obviously more than one) for this new genus and species were from Discovery -Expedition Stat. 474, one sea mile west of Shag Rock, South Georgia, 199 m. No registration numbers are recorded, or precise number of specimens, but a “ Type ” is referred to. The descriptions are diagnostic and accord closely with the description above, except that no measurements were given for specimens or ossicles. Panning wrote that the work on the Discovery material was taken over by Dr. Deichmann. This was not completed, and no Discovery Report has been published. All of the Discovery holothuroids that remained on loan to the Smithsonian US National Museum of Natural History are currently (December 2008) in Museum Victoria for determination, on their way back to the British Museum of Natural History. The types for Parathyonidium incertum Heding, 1954 are not with the Discovery lots currently in Museum Victoria. It is reported (David Pawson, pers. comm.) that a paratype from Elephant Island is in the Paris Museum. The holotype has not been located.