Lissoclinum levitum Kott, 2001

Kott, Patricia, 2004, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part I), Journal of Natural History 38 (19), pp. 731-774 : 767-768

Lissoclinum levitum Kott, 2001

( figure 20A, B )

Lissoclinum levitum Kott, 2001: 307 .

Distribution. New records: South Australia (Golden I., Avoid Bay, SAM E3204; Kangaroo I., SAM E2924). Previously recorded (see Kott, 2001): South Australia (Ward I.). The species is known only from South Australia.

Description. In preservative, the newly recorded colonies are soft, grey sheets. An in situ photograph of one of these colonies (SAM E3204) shows it to have been pink and translucent in life, with rounded elevations on the surface, each with a large terminal common cloacal aperture. These elevations appear to be formed by thickening of the basal test to form a central test core, often mixed with debris. Branchial apertures, each surrounded by a ring of spicule-free test, have crowded clumps of spicules in the six lobes around each opening and are depressed into the surface of the colony. Spicules are sparsely distributed in thin layers, one in the surface, another in the basal test. Also a few spicules may be scattered in the strands of test in which the zooids are suspended between the surface and the basal test. These strands of test consist of a common basal connective, which sometimes is very long. It branches at the posterior end of groups of about eight zooids, separating them completely from each other in independent sheaths of test, each surrounded by common cloacal cavity. In some parts of the colony the basal stem of the test connectives is very short and each zooid appears to cross the common cloacal cavity separately. Sometimes some small developing groups of zooids are in the basal test clustered around the base of the test connective. Spicules are stellate, to 0.06 mm diameter with 9–13 conical rays in optical transverse section.

Zooids are relatively large (1.5 mm) and delicate without conspicuous muscles. The branchial aperture is six-lobed on a short siphon and the atrial opening is large and sessile, exposing the branchial sac directly to the common cloacal cavity. About eight large stigmata are in the anterior row in the branchial sac. The gut is roomy and makes a wide horizontal loop behind the branchial sac. A large two-lobed testis is behind the ventrally flexed gut loop and the vas deferens, expanded into a thick seminal vesicle at its proximal end, curves around to the dorsal surface in the groove between the two testis follicles. A large concave lateral organ is on each side of the thorax near the ventral end of the third row of stigmata. Larvae are not known.

Remarks. The species is readily distinguished by its relatively large stellate spicules, which are not usually found in this genus. They are larger than reported for the holotype in which, although they are in poor condition, spicules larger than 0.04 mm diameter have not been encountered (see Kott, 2001). There also is some variation in the size of the common cloacal cavity which is more restricted in the holotype (see Kott, 2001), having the abdomina embedded in the basal test rather than in the ligament joining the surface to the basal test where they are in more recently recorded specimens. It seems likely that the development of the common cloacal cavity is related to the growth of the colony.

This thin, transparent, encrusting colony looks like Diplosoma listerianum (with which it often is taken) although the presence of spicules readily distinguishes it from the latter species. It is distinguished from other Lissoclinum spp. by its stellate, rather than small burr-like spicules, and by their sparse distribution. The tropical L. maculatum Kott, 2001 has spicules sparsely distributed in the middle layers of the colony but is distinguished by their burr-like form and by the presence of an undivided testis.

Figures

FIG. 20. Lissoclinum levitum (SAM E3204): (A) abdomen; (B) spicules. Lissoclinum pacificense (QM G300973): (C) spicules. Lissoclinum patella (ZMA TU500): (D) spicules. Scale: (A) 0.1 mm.