Diplosoma velatum 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 : 772-773

Diplosoma velatum Kott, 2001

( figure 22 )

Diplosoma velatum Kott, 2001: 345 and synonymy.

Distribution. New records: Western Australia (Oyster Harbour, Albany, WAM 138.93), South Australia (Kangaroo I., SAM E2857, E2910, E2921), Victoria (Bass Strait, QM G12743–4). Previously recorded (see Kott, 2001): Western Australia (Albany, Esperance), South Australia (York Peninsula, Eyre Peninsula, Spencer Gulf, Investigator Strait), Victoria (Western Port).

Description. One of the newly recorded colonies (SAM E2910) is about 5 cm diameter with a deep, cup-shaped concavity basally (probably once enveloping a rounded pebble) and the upper convex surface raised into intertwining serpentine rounded ridges containing a core of the basal test, and with zooids opening all around the outer surface; another (QM G12744) has cylindrical, finger-like or irregular lobes projecting from the upper surface of the basal mat-like part of the colony. The other newly recorded colonies are the usual fleshy, encrusting masses previously reported for the species. Always, the zooids are clumped together in groups of about 20, each clump attached to the central or basal test by a broad connective. The vast common cloacal cavity penetrates around the thoraces. The test is soft, translucent and the whole colony is cream. Zooids are as previously described with the large branchial sac exposed directly to the common cloacal cavity and two testis follicles. Embryos are crowded in the central or basal test of specimens collected in September (WAM 138.93) and May (SAM E2910). The almost spherical larval trunk is about 1.0 mm long. An oozooid and thoracic and abdominal buds, and four pairs of lateral ampullae are present and the sensory vesicle projects up from the oozooid into the larval test. The tail is relatively short, being wound only halfway around the trunk. Irregular opaque bodies are in the larval test around the oozooid and blastozooid.

Remarks. The raised surface ridges and projecting lobes have not been described previously for this species. Superficially such colonies look like Trididemnum spp. (e.g. T. nobile ) and some Didemnum psammatode in which the lobes appear to overgrow the surface, although in the present species the surface ridges may not have developed in the same way.

Zooids lack the black squamous epithelium of D. listerianum .

Figures

FIG. 22. Diplosoma velatum (SAM E2910): (A) zooid; (B) larva. Scales: (A, B) 0.1 mm.