Trachythyone muricata Studer 1876

Trachythyone muricata Studer, 1876

Trachythyone muricata Studer, 1876: 453.

Thyone recurvata Théel, 1886: 94, pl. 5 fig. 7, pl. 8 fig. 6. Cucumaria squamata Ludwig, 1898: 27 –28, pl. 1 figs 19–21. Trachythyone squamata.— Hernández, 1987: 163.

Remarks. Trachythyone muricata is the type species for Trachythyone Studer, 1876, and the Kerguelen Is are the type locality. The holotype of Trachythyone muricata (Museum fuer Naturkunde, Humboldt–Universitaet zu Berlin, ZMB 2252) is characterized by: fusiform elongate body, 70 mm long (90 mm long in Studer 1876), 12 mm mid-body diameter, long posterior taper; calcareous rugose body; tube feet cover body, hard, not retractile, no bare interradii; 10 dendritic tentacles, 2 ventral smaller; calcareous ring lacking posterior prolongations; body wall ossicles plates and cups; plates thick, single-layered, perforations small, some ridge thickenings but lacking knobs and spines, irregularly elongate, up to 596 µ m long; cups thick, deep, oval to rectangular, up to 88 µ m long, bluntly spinous rim, sometimes with bridges across rim. Trachythyone muricata is represented in the BANZARE collection by a single small specimen. It is represented in the SAM collections from Heard I. by an 82 mm long specimen (SAM K2302).

The description and figures for the single specimen of Thyone recurvata Théel, 1886 (type locality Kerguelen Is) are the same as the diagnostic characters of the type for Trachythyone muricata, and it is judged here to be a junior synonym. Cucumaria squamata Ludwig, 1898 was described for a single 30 mm long specimen from Betsy Cove (Kerguelen I.). The large smooth perforated plates and small rectangular bluntly spinous cups are diagnostically identical with the body wall ossicles of Trachythyone muricata, and it is judged here to be a junior synonym.

Ekman (1925) thought that Thyone muricata and Thyone recurvata (both with type locality Kerguelen Is) might be junior synonyms of Cucumaria parva Ludwig, 1874 (type locality Magellanic region; referred to Trachythyone by Panning 1949). Ekman (1927) subsequently listed Trachythyone muricata and Thyone recurvata as junior synonyms of Cucumaria parva. Ludwig & Heding (1935) distinguished Thyone muricata from their new species Cucumaria (Semperia) ekmani (type locality Kerguelen Is; synonymised above with Neopsolidium kerguelensis), but did not give an opinion on a relationship with Thyone recurvata. Panning (1964) also thought that Trachythyone muricata might be a junior synonym of Trachythyone parva. In a species list for Terre Adélie, Cherbonnier (1974a) listed Trachythyone muricata as a junior synonym of Trachythyone parva. I have found Trachythyone bouvetensis (Ludwig & Heding, 1935) in both the Ross Sea (New Zealand Institute of Water and Atmospheric Research, NIWA) and Prydz Bay (NMV) collections, and anticipate that the Terre Adélie specimens are Trachythyone bouvetensis. A possible synonymy of the geographically widely separated species T. muricata and T. parva is rejected here since T. parva has: smaller size, up to 31 mm long (Perrier 1905); tube feet confined predominantly to radii, especially ventrally; tube feet not noticeably hard and non-retractile; smaller perforated plate ossicles, 150 µ m long (Perrier 1905).

The Antarctic and Sub-Antarctic species Trachythyone bouvetensis (type locality Bouvet I.) is covered dorsally and laterally by tube feet. It is distinguished from Trachythyone muricata by: distinct “belly” midbody, not fusiform; tube feet not noticeably hard, non-retractile; bare ventral interradii; large perforated plates (up to 520 µ m long) frequently with four larger central perforations, sometimes sharply to bluntly spinous at one end; cups and cupped crosses up to 96 µ m long, with long pointed spines.

The type species for the genus Trachythyone is completely covered by tube feet. Panning (1964) diagnosed the genus Trachythyone to include both radial only or overall distributions of tube feet. Trachythyone cynthiae sp. nov. and Trachythyone mackenzieae sp. nov. (above) have radial only series of tube feet. It is noted above that Neopsolidium Pawson is diagnostically very close to Trachythyone. Resolution of these systematic issues should await evidence from molecular genetic data.