Didemnum studeri Hartmeyer, 1911

Turon, Xavier, Cañete, Juan I., Sellanes, Javier, Rocha, Rosana M. & López-Legentil, Susanna, 2016, Ascidian fauna (Tunicata, Ascidiacea) of subantarctic and temperate regions of Chile, Zootaxa 4093 (2), pp. 151-180 : 154-156

Didemnum studeri Hartmeyer, 1911

Fig. 3 A,B,E; Fig. 12 D

References and synonymy: Didemnum studeri Millar (1960) p. 56; Kott (1969) p. 75; Monniot (1970) p. 335. Localities: 1S, 2S, 3S, 6S, 9S.

Whitish colonies forming extensive crusts, up to tens of cm in diameter and 3–4 mm in thickness. The tunic is filled with spicules 10–30 µm in size, stellate with about 8–9 short rays in optical section. Often, rays are blunt and irregular, giving an almost spherical appearance to the spicule. The general cavity is extensive at the thoracic level, often with accumulated faecal pellets.

The zooids are small and highly contracted. The branchial sac has a large aperture and 4 rows of stigmata. The thoracic organs lie at the posterior part of the branchial sac. There is a developed retractor muscle. The abdomina are embedded in the basal test and do not have gonads in the observed specimens.

Some colonies incubate larvae, 0.6 mm in trunk length, with three adhesive papillae and four pairs of ectodermal ampullae.

Remarks. this species is common in Antarctic and subantarctic waters (Monniot & Monniot 1983). Although we couldn’t observe gonads in our material, the spicules, larvae and general shape of colonies and zooids allows the assignment of our specimens to this species.

Figures

FIGURE 3. Didemnid species. Didemnum studeri: A, colonies, B, anterior region of a larva; Polysyncraton trivolutum: C, image of a colony, D, thorax in dorsal (left) and lateral (right) view; E, spicules of Didemnum studeri; F, spicule of Lissoclinum perforatum; G, spicule of Polysyncraton trivolutum. Scale bars: A, 5 cm; B, 0.1 mm; C, 1 cm; D, 0.25 mm; E, 10 µm; F, 5 µm; G, 1 0 µ m.

FIGURE 12. Polyzoa opuntia. A, colonies; B, zooid dissected without branchial sac (stained), inset shows magnification of gonads and endocarps on the left side. Scale bars: A, 2 cm, B, 1 cm.