Parathyonidium incertum Heding, 1954

O’Loughlin, P. Mark, Mackenzie, Melanie, Paulay, Gustav & VandenSpiegel, Didier, 2014, Four new species and a new genus of Antarctic sea cucumbers with taxonomic reviews of Cladodactyla, Pseudocnus, Paracucumidae and Parathyonidium (Echinodermata: Holothuroidea: Dendrochirotida), Memoirs of Museum Victoria 72, pp. 31-61 : 55-57

Parathyonidium incertum Heding, 1954

Figure 15

Parathyonidium incertum Heding, 1954 in Heding and Panning 1954: 37–39, text fig. 3.— O’Loughlin et al., 2009b: 5–6, table 1, fig. 1d–f.—O’Loughlin et al., 2010: table 1.

Parathyonidium Heding species. — O’Loughlin et al., 2009a: 217, fig. 2c.

Parathyonidium species. —O’Loughlin et al., 2010: 4, table 1.

Material examined. Holotype. West of Shag Rock , South Georgia, Discovery Expedition, RRS Discovery II stn 474, 199 m, 12 Nov 1930, no registration found (data from Heding and Panning 1954; specimen not located).

Paratypes. South Shetland Islands, Clarence Island, Discovery Expedition , Discovery stn D170, 61º26'S 53º46'W, 342 m, 23 Feb 1927, NHMUK 2011.171 – 173 (3); ZMUC –HOL–300 (3) (confirmed by Tom Schioette ZMUC; specimens not seen here); Elephant I., 600 m, MNHN – IE –2013–2479 (2) (previously EcHh250, confirmed by Sébastien Soubzmaigne MNHN; specimens not seen here) .

Other material. South Atlantic Ocean , South Georgia, US AMLR 2004 , Icefish stn 47–BT25, 55.06ºS 35.24ºW, 116 m, 12 Jun 2004, NMV F104998 (1) ; Antarctic Peninsula , Low I., BENTART–2006, R / V Hesperides , stn LOW47, 63.47ºS, 62.22ºW, 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 NMV F161526 , tentacle ossicles slide NMV F161527 ; Eastern Antarctica, off Enderby Land, Nella Dan, ANARE stn HRD010, 65º56'S 50º52'E, 386–400 m, M. Norman, 15 Nov 1985, NMV F84983 (15) , NMV F165585 (1) , NMV F189876 (4) ; stn HRD011, 65º50'S 50º35'E, 540 m, M. Norman, 20 Nov 1985, NMV F189880 (2).

Description (emended from O’Loughlin et al. 2009b). Specimens up to 35 mm long preserved (tentacles partly extended, NMV F104998), sub-cylindrical, elongate, widest diameter 5 mm; soft thick body wall; lacking distinct ventral sole; oral end sometimes upturned, slightly tapered and rounded distally when tentacles withdrawn; anal end slightly tapered and rounded distally; 13 to 16 dendritic tentacles (holotype with 13; NMV F104998 with 16; one paratype NHMUK 2011.171–173 with 15), typically in a single circle of 5 single, smaller, radial and 5 pairs of larger, inter-radial tentacles; long digitiform genital papilla posterior to dorsal tentacle pair immediately distal to tentacle crown in male specimen (suggesting internal fertilization and brood protection); female genital pore posterior to dorsal tentacle pair; tube feet large, confined to radii, spaced in single series from base of tentacles to anus; calcareous ring with radial plates only, sub-rectangular, elongate, wide anteriorly and posteriorly, narrowed mid-plate, deep posterior notch; 1–2 long, tubular polian vesicles; no respiratory trees; gonad tubules in two tufts, not in series along gonoduct, one tuft on each side of dorsal mesentery, tubules not branched; brood-protection of free juveniles in the coelom.

Body wall ossicles two types of plates: abundant, thin, lattice-like, smooth to knobbed, single-layered, irregular plates, with bluntly denticulate margins, and with few to many perforations, similar dorsally and ventrally; and additional thin, elongate, plates, with 2 large central perforations, 2 small distal perforations, with one end extended with few small perforations, and with short blunt denticulations on surface and around margin, typically 100 μ m long, but up to 160 μ m long; these small plates intergrade with the larger smooth to knobbed, marginally denticulate plates, that are up to 200 μ m long. Tube foot with large (up to 360 μ m diameter) endplates, few perforated support plates. Tentacle ossicles perforated round to oval, slightly concave plates, with blunt marginal denticulations, some with central knob, some fine surface spines, plates up to 280 μ m long; rods absent. Peri-anal body wall with incipiently multi-layered, thick, round, perforated plates / scales, 440 μ m diameter.

Colour (preserved). Yellow-white, some specimens with a violet hue; purple internally ( Heding 1954), pale grey (this work).

Distribution. South Atlantic, South Georgia, Shag Rock; Western Antarctica, Elephant I. , South Shetland Is, Antarctic Peninsula; Eastern Antarctica, Enderby Land ; 115– 600 m.

Remarks. Heding and Panning (1954) makes clear reference to a “Type” from Shag Rock, and also refers in the description to additional specimens. This holotype has not been located in any of the European or United States museums. There are paratypes so labelled in the MNHN and ZMUC. Amongst the Discovery Expedition specimens there are three from Clarence Island in the South Shetland Islands ( NHMUK 2011.171–173) that are from the same original lot as the labelled paratypes in Copenhagen ( ZMUC –HOL–300 (3)). We have labelled and listed these NHMUK specimens as paratypes. We have found numerous specimens from off Enderby Land in Eastern Antarctica in the collections of Museum Victoria ( NMV). These coelomic brood-protecting specimens were first thought to represent a new species (see O’Loughlin et al. 2009a, 2010), but we now judge that they are conspecific with Parathyonidium incertum . This is the only Antarctic coelomic brood-protecting species reported to date (see O’Loughlin et al. 2009a).

Figures

Figure 15. Parathyonidium incertum Heding, 1954. a–c, paratypes NHMUK 2011.171–173. a, specimen showing large radial tube feet, and smaller tentacle aligned with radius / ambulacrum (oeophagus everted); b, dorsal inter-radial male genital papilla immediately distal to tentacle crown; c, view of tentacle crown with smallest tentacles aligned with radii / ambulacra (denoted by red spot; top right small tentacle obscured by larger tentacle). d–f, specimen NMV F104998. d, SEM images of ossicles from tentacles; e, SEM images of ossicles from dorsal mid-body wall; f, SEM images of ossicles from ventral mid-body wall.