Didemnum abradatum, Kott, 2007

Kott, Patricia, 2007, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 4), Journal of Natural History 41 (17 - 20), pp. 1163-1211 : 1175-1176

Didemnum abradatum sp. nov.

( Figures 2A, B , 7F )

Distribution

Type locality: Queensland (Great Barrier Reef: 18.325 ° S, 146.595 ° E, 41 m, Biodiversity Survey SBD 504398 sample 2419, 11 October 2003, holotype QM G308870 ) .

Description

Encrusting colonies have spicules crowded throughout and a thoracic common cloacal cavity. Spicules, to 0.0375 mm diameter, have 13–15 not particularly crowded short conical rays in optical transverse section. Zooids are small with a moderately long branchial siphon which is wine glass-shaped when contracted. A tapered retractor muscle projects from halfway down the long oesophageal neck. The atrial aperture is a sessile opening without an anterior lip. The testis is entire but the vas deferens was not detected. Larvae have the usual three rows of stigmata in a rounded trunk 0.4 mm long. The tail almost completely encircles the trunk (five-sixths of the way around it). Four long, club-shaped ectodermal ampullae are on each side of the three anteromedian adhesive organs.

Remarks

Didemnum paa C. and F. Monniot, 1987 has similar spicules, although they are larger than the present species, have long, crowded rays and the larvae have a trunk about 0.3 mm long and four pairs of ectodermal ampullae. Didemnum fibriae Kott, 2004a has spicules of a similar size and form, but a larger larval trunk with blastozooids and more ectodermal ampullae than the present species. Didemnum mutabile is distinguished from the present species by its five pairs of larval ampullae and an atrial tongue.

Figures

Figure 2. (A, B) Didemnum abradatum (QM G308870, holotype): (A) zooid; (B) larva. (C, D) Didemnum fragum (QM G308826): (C) colony; (D) larva. (E) Didemnum jedanense (QM G308862): larva. Scale bars: 0.1 mm (A, B, D, E); 1 cm (C).

Figure 7. Scanning electron micrographs. (A) Polysyncraton magnetae (QM G308818); (B) Polysyncraton meandratum (QM G308849); (C) Polysyncraton otuetue (QM G308851); (D) Polysyncraton reticulum (QM G323330); (E) Polysyncraton scorteum (QM G323343); (F) Didemnum abradatum (QM G308870); (G) Didemnum astrum (QM G308857); (H) Didemnum candidum (QM G308765).