Didemnum, Savigny, 1816

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 : 1192-1193

Didemnum IJesica sp. nov.

( Figures 4D , 10F )

Distribution

Type locality: Queensland (Great Barrier Reef: 14.715 ° S, 145.405 ° E, 26 m, SBD 504379 sample 1751, 5 October 2003, holotype QM G308874 ; 17.445 ° S, 146.205 ° E, 26 m, paratype QM G308875 ) .

Description

The holotype colony is a large encrusting sheet with a dark mesh on the surface over the primary common cloacal canals which are lined by zooids and surround the zooidfree areas where spicules are crowded. Spicules are not in the test over the common cloacal canals. Spicules are small, to 0.03 mm diameter, burr-like with rod-shaped rays. A spicule-free layer of bladder cells is over the surface and bladder cells are present throughout the test. Black pigment particles are in patches in the surface, as well as in the middle layer of the colony (around the zooids). Deep circular primary common cloacal canals are lined on each side by zooids. Zooids are robust with a moderately long branchial aperture and a long, very fine retractor muscle. Seven coils of the vas deferens surround the undivided testis.

Remarks

The specimens resemble Didemnum parau C. and F. Monniot, 1987. Although six coils of the vas deferens are reported, there are seven and eight coils, respectively, in the figures of the type material of D. parau ( Monniot and Monniot 1987, Figure 12B, C). The small burr-shaped spicules (to 0.03 mm diameter) with rod-like rays and the larvae (with four pairs of ectodermal ampullae) are in D. parau as well as in the present species. The type specimens of D. parau had various organic particles embedded in the basal test of the soft colonies, although the clumps of plant cells found in the present specimens were not reported. The present species is distinguished from D. parau by the surface layer of bladder cells and their presence throughout the test and the large black pigment cells in the test.

Kott (2001) compared D. parau and D. fragile Sluiter, 1909 , which both have burrshaped spicules and similar zooids. Didemnum fragile has larger spicules than either D. parau or the present species; like D. parau , it lacks the bladder cells and pigment of the present species; it has only six coils of the vas deferens; and it has five pairs of larval ampullae rather than the four of the present species.

Didemnum chartaceum Sluiter, 1900 resembles the present species in its superficial bladder cells and their presence throughout the colony and in its large pigment cells. However, it has different spicules, nine coils of the vas deferens, and a large larva.

Figures

Figure 4. (A–C) Didemnum tantulum (QM G308890, holotype): (A) thorax; (B) abdomen; (C) larva. (D) Didemnum υesica (QM G308874, holotype): zooid. Scale bars: 0.1 mm.

Figure 10. Scanning electron micrographs. (A–C) Didemnum psammatode [(A, B) QM G308820; (C) QM G308831]; (D) Didemnum tantalum (QM G308860); (E) Didemnum tumulatum (QM G308873); (F) Didemnum υesica (QM G308875); (G) Didemnum υiride (QM G308864); (H) Trididemnum farrago (QM G308819).