Thysanocardia catharinae Grube 1868

Thysanocardia catharinae (Grübe, 1868)

(Fig. 2 C)

Material. Nha Trang Bay: Mung Island, 12–25 m depth, muddy sand, 5 specimens.

Description. Spindle-shaped, sand-coloured trunk 3–9 mm long, 1–1.5 mm wide, with minute papillae and characteristic sinuous wrinkles of cuticular microrelief; introvert subequal to or 1.5 X trunk length. Tentacular apparatus with dorsal arc of tentacles, oral crown with longitudinal festoon of tentacles; tentacles of living specimens with yellow tips, colourless in fixed worms. Body wall with continuous muscle layers. Two wide retractor muscles originate in the posterior trunk, about 10–15% of trunk length from the posterior end. Gut with 6–10 loops. Spindle muscle not attached posteriorly. Contractile vessel with numerous villi. Nephridia are free, about 35% of trunk length; nephridiopores are at the level of the anus.

Discussion. There are only three species known for this genus worldwide. T. nigra can be well separated from T. catharinae by presence of dark pigments in colored tentacles of both dorsal and oral tentacular crowns. T. nigra is also characterized by having long branched contractile vessel villi. Both species are common in North-West Pacific, while the third species, T. procera, is known only from the Atlantic.

Thysanocardia catharinae has a temperate and tropical distribution, can be found mainly subtidally inhabiting sand, silty sand, and dead corals. It is known in the West Pacific from the Gulf of Siam to the Sea of Japan.