Didemnum spumosum, Kott, 2004

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 : 758-760

Didemnum spumosum sp. nov.

( figure 15 )

Distribution. Type locality: New South Wales (Coffs Harbour on jetty piles,

0–5 m, coll. J. E. Watson, 12 December 1972, holotype MV F53285 ).

Description. The colony is complex: folded, with parts of its surface coalescing. The common cloacal cavity is at thorax level, and the common cloacal apertures are inconspicuous and sessile. Spicules are in a layer at the surface but are not crowded. They are stellate, to 0.04 mm diameter, with 13–15 pointed, blunt or round-tipped rays in optical transverse section. In preservative the colony is pinkish and translucent.

Zooids are small, although eight stigmata are in the anterior row. The branchial siphon is short and the aperture six-lobed. A sessile, transverse atrial aperture exposes the centre of the branchial sac to the atrial cavity. A fine retractor muscle projects from halfway down the oesophageal neck. Cup-shaped lateral organs with the concavity directed ventrally project from each side of the endostyle. The gut forms a double loop and about four short stolonic vessels with rounded terminal ampullae project from its ventral concavity. The vas deferens coils 10 times around an undivided testis. Embryos are being incubated in the basal test. The larval trunk is 0.75 mm long with the tail wound two-thirds of the way around it, four lateral ampullae each side of the antero-median adhesive organs, a well-formed oozooid with three rows of stigmata, and otolith and ocellus about halfway along the trunk. Blastozooids are not present.

Remarks. Didemnum jedanense Sluiter, 1909 has similar spicules and large larvae to the present species, equally fleshy and sometimes complex colonies, and is often almost completely aspiculate. However, D. jedanense has more larval ectodermal ampullae, blastozooids and fewer vas deferens coils. The present species is characterized by its lobed and complex colony, double gut loop, relatively few and burr-like spicules, large number of vas deferens coils, and the size of its larval trunk.

Didemnum ? stragulum Kott, 2001 Didemnum stragulum Kott, 2001: 238 .

Distribution. New record: Western Australia (Montebello Is, WAM 157.93). Previously recorded (see Kott, 2001): Eastern Indian Ocean, Indonesia, Heron I., New Caledonia.

Description. The newly recorded colony is thin, irregular and encrusts a sponge. On some parts of the surface (though not all) the characteristic pointed papillae are at the ventral side of each branchial aperture. Spicules have the same range in the number of rays (7–11) as the type material and are to 0.09 mm diameter. Common cloacal spaces were not detected. Zooids are small, with a moderately long to short stumpy retractor muscle. Gonads were not detected.

Remarks. The spicules and the general form of the zooids of this immature colony resemble previously recorded material of this species and distinguish it from others known from this region

Figures

FIG. 15. Didemnum spumosum (MV F53285): (A) colony; (B) thorax; (C) abdomen; (D) larva; (E) spicules. Scales: (A) 2.0 cm; (B–D) 0.1 mm.