Molpadia violacea Studer, 1876

O'Loughlin, P. Mark, Skarbnik-López, Jessica, Mackenzie, Melanie & VandenSpiegel, Didier, 2015, Sea cucumbers of the Kerguelen Plateau, with descriptions of new genus and species (Echinodermata: Holothuroidea), Memoirs of Museum Victoria 73, pp. 59-93 : 87-91

Molpadia violacea Studer, 1876

Tables 1–6; figures 1, 14, 15 e, f.

Molpadia violacea Studer, 1876: 464 .— Pawson, 1963: 15, pl. 3, figs 4–8.—1965: 12.

Trochostoma violaceum . — Théel, 1886: 42–43, pl. 2, fig. 4, pl. 11, fig. 1.— Lampert, 1889: 842.— Ludwig, 1894: 157–158.— 1898: 64.— Perrier, 1905: 65–66.

Haplodactyla violacea .— Heding, 1931: 280.

Eumolpadia violacea . — Heding, 1935: 42, text fig. 8, figs 7–10; pl. 5 fig. 10; pl. 7, fig. 3; pl. 8, fig.4.— Ludwig & Heding, 1935: 144–145, text fig. 11.— Cherbonnier & Guille, 1975: 609.

Molpadia musculus Risso, 1826 (Antarctic).— O’Loughlin et al., 2009: table 1.—O’Loughlin et al., 2010: 269(6), tables 1, 2, 4, fig. 2 (non Molpadia musculus Risso, 1826 ).

Molpadia musculus (HOL 12).—Hibberd & Moore, 2014: 42, 119, 145 (non Molpadia musculus Risso, 1826 ).

Material examined. Holotype. Southern Ocean , N Kerguelen Plateau, SMS Gazelle 1874, Kerguelen Islands, 183 m, ZMB 2070 .

Other material ( AAD species code: HOL 12 ). HIMI, Aurora Bank, SC 26(179), -52.48 71.75, 275 m, 1 May 2003, TMAG H3540 (1) ; SC26(193), -52.42 71.87, 264 m, AAD ; Southern Shell Bank , SC26(263), -51.80 75.50, 628 m, TMAG H3433 (4) ; SC26(267), -51.82 76.02, 472 m, 10 May 2003, TMAG H3541 (1) ; Shell Bank MR, SC46(128), -51.55 75.76, 337 m, AAD ; off Heard I., AD67(40), -52.95 73.34, 112 m, NMV F76842 (1) ; Pike Bank , SC50(10), -51.31 71.77, 273 m, NMV F165737 (1) ( UF tissue sequence code MOL AF667 ) .

Eastern Antarctica, Prydz Bay, AA91(84), -68.05 73.18, 680 m, NMV F71992 (1).

Western Antarctica, South Shetland Islands, AMLR 2003(71), -62.44 -61.14, 138 m, NMV F104825 (1) ( UF tissue sequence code MOL AF 574); South Shetland Islands, LI–AGT–3, -62.40 -61.76, 556 m, NMV F168644 (3) ( UF tissue sequence code MOL AF 809); South Orkney Islands, US AMLR 2009(104), -63.23 -59.46, 757–783 m, NMV F169293 (4); South Orkney Islands, US AMLR 2009(41–42), -61.82 -46.19, 450–461 m, NMV F169294 (1); South Orkney Islands, US AMLR 2009(21), -61.06 -42.84, 422–428 m, NMV F169295 (1); off Hugo I., -64.74 -65.48, 684–705 m, NMV F169353 (1); South Shetland Islands, US AMLR 2012(247), -62.38 -61.42, 344 m, NMV F193760 (5).

Description. Body up to 145 mm long, up to 25 mm diameter (preserved, NMV F169293, South Shetland Is), body form cylindrical mid-body with short anterior taper to blunt rounded end, posterior taper to short discrete thin tail, about 10% of body length, body wall firm, leathery. Tentacles 15, digitiform, each with single terminal digit. Calcareous ring solid, plates fused, radials wider than inter-radials, radials with two anterior lateral rounded projections, one with longitudinal muscle attachment and anterior notch with anterior ends of notch incurved and almost closed, tapered posterior prolongation with small bifid posterior notch; inter-radials with pointed anterior projection, broad rounded posterior indentation. Length of tentacle ampullae more than twice the height of the ring. Single polian vesicle tubular, long. Long stone canal with spiral form; madreporite attached to body wall. Longitudinal muscles broad, flat, each divided along mid-line by wide gap. Gonad tubules branched.

Ossicles tables and fusiform rods, tables and rods in main body wall, rods only caudally, in larger specimens main body tables and fusiform rods variably to completely phosphatised; tri-radiate table discs with predominantly three perforations, often a few more than three, discs frequently irregular, disc margin smooth or frequently with short to long rod-like projections from margin distal to perforations, discs variable in size, up to 190 µ m across (excluding rod-like extensions from margin), solid columnar spires with blunt distal spines, spires about 70 µ m high, tables phosphatize into reddishorange bodies; long fusiform rods in mid-body and tail, rods widened centrally with elongate perforation with irregular thin bridging rods creating 2–6 irregular perforations, predominantly 3, rods variable in length, mid-body rods up to up to 1300 µ m long, only rods in mid-body phosphatize, caudal fusiform rods smaller than in mid-body, up to 900 µ m long, mid-body and caudal fusiform rods never with solid spire similar to tables. Inconspicuous anal scales in peri-anal body wall, irregular columnar form, comprise a dense rod network, scales up to about 360 µ m long. Anchors or racquet-shaped plates not observed. Ossicles phosphatising to red, orange and yellow irregularly oval bodies or clusters of granules, sizes vary.

Colour of preserved body variable: oral end and discrete tail frequently off-white; body off-white to blue-grey to grey with fine black to red phosphatic spots or flecks; varying to coalescing spots creating a dark red to black colour with a red-brown hue. Live holotype violet ( Studer, 1876).

Distribution. Southern Ocean, Kerguelen Plateau, Kerguelen Islands, Aurora, Pike, Shell Banks, Heard I., 112– 628 m. Antarctica, Prydz Bay, Ross Sea and vicinity of the South Orkney and South Shetland Islands.

Remarks. Clark (1908) and Deichmann (1940) were of the opinion that Molpadia violacea Studer, 1876 is a junior synonym of Molpadia musculus Risso, 1826 . This opinion was discussed and upheld emphatically by Pawson (1977). After examining many specimens of Mopadia of different sizes, Pawson (1977) had observed the great variability of ossicle form within the same species. Pawson (1977) finally judged that M. musculus was cosmopolitan in distribution with a wide bathymetric range of 35–5205 m. O’Loughlin et al. (2010) list Molpadia musculus Risso, 1826 from Antarctica.

O’Loughlin et al. (2010) also showed that recent molecular phylogenetic data are revealing many cryptic species and they provided a phylogenetic tree for CO1 sequence data from 19 specimens judged to be Molpadia musculus . The specimens were collected from the Amundsen Sea, Ross Sea and South Shetland Islands in Antarctica, from Heard Island, and from Western Australia. The tree indicates the probability of five cryptic species. One of the species is Antarctic, with specimens from the Ross Sea and the South Shetland Islands, and this clade includes the specimen from Heard Island. None of the five cryptic species includes a specimen from the Mediterranean Sea, the type locality for Molpadia musculus . We judge from these data, and the geographical separation, that none of these specimens represents Molpadia musculus . We thus raise Molpadia violacea Studer, 1876 out of synonymy with Molpadia musculus Risso, 1826 , and note that Antarctic Molpadia specimens previously referred to M. musculus should in some cases now be referred to Molpadia violacea .

We have examined specimens of Molpadia from Western Antarctica that were previously thought to be Molpadia musculus and based on colour, ossicle form and occurrence, the phosphatising and disappearance of calcareous ossicles, the absence of spires on caudal fusiform rods, and in two cases with the support of the genetic data in O’Loughlin et al. (2010), we refer them to Molpadia violacea . These are listed above. We found only one specimen ( NMV F71992) that was collected from Prydz Bay that appears to be Molpadia violacea . It exhibits appropriate colouration, no spires on caudal fusiform rods, and abundant phosphatic bodies in the body wall.

We have identified a number of specimens that were previously thought to be Molpadia musculus , from Prydz Bay in Eastern Antarctica and the Amundsen Sea in Western Antarctica, as Molpadia magdae O’Loughlin (in O’Loughlin et al. 2013): from Prydz Bay lots NMV F68058 (1), NMV F197215 (2), NMV F68677 (1), NMV F71993; and from the Amundsen Sea lot NMV F168645 (1). These specimens are characterized by: lack of colour and minimal phosphatizing; a body cover of table spires; irregular triradiate table discs that frequently have long rod-like marginal elongations; and asymmetrical fusiform rods caudally, some of which have spires and inter-grade with tables (see Figure 15 a–d ). Molpadia magdae was described from the South Shetland Islands and this work extends its distribution to Prydz Bay in Eastern Antarctica. We have never detected spires on caudal fusiform rods in specimens of Molpadia violacea .

Figures

Figure 15. Microscope photos of ossicles and phosphatic bodies from specimens of Molpadia magdae O’Loughlin (in O’Loughlin et al. 2013) and Molpadia violacea Studer, 1876. a–d, Molpadia magdae. a, mid-body irregular table discs, ossicles beginning to phosphatize with small phosphatic bodies present (from NMV F197215); b, caudal fusiform rods, some only with spires (from NMV F197215); c, mid-body irregular table discs and fusiform rod, ossicles beginning to phosphatize (from NMV F68677); d, caudal fusiform rods, one with and one lacking spire (from NMV F68677); e–f, Molpadia violacea. e, mid-body phosphatizing table disc (disc 64 µm across; from NMV F165737); f, mid-body phosphatic bodies (from NMV F169293).