Didemnum nekozita Tokioka, 1967

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 : 754-756

Didemnum nekozita Tokioka, 1967

( figure 13 )

Didemnum nekozita Tokioka, 1967: 67 .

Didemnum anoi Monniot and Monniot, 1987: 25 .

Didemnum moseleyi: Eldredge, 1967: 211 (part, specimen from Eniwetak).

Didemnum cuculliferum: Kott, 1981: 164 ; Kott, 2001: 167 (part, newly recorded specimens and synonyms as above); Monniot and Monniot, 2001: 267.

Distribution. New record: Western Australia (N side of Ashmore Reef, WAM

201.90; South Passage Shark Bay, 12–16 m, WAM 151.93). Previously recorded (see Kott, 2001): Queensland (Capricorn Group, Lizard I.), Palau Is, Philippines, Fiji, Eniwetak, French Polynesia.

Description. Newly recorded colonies are small (to 1.5 cm long and 1.0 mm thick) longish oval cushions, attached to weed, sometimes with an irregular slightly lobed margin (possibly lobulating). Spicules are crowded throughout, some spicule-filled minute papillae are on parts of the colony surface and spicules line margins of the stellate branchial apertures. On parts of the colony surface branchial apertures are protected by a larger pointed papilla. Common cloacal apertures are in the middle of the upper surface or are terminal on projecting lobes or branches. Clumps of abdomina project up into the floor of extensive thoracic common cloacal cavities roofed over by a thin layer of surface test. Basal test or the central core (in cylindrical colonies or lobes) is solid and crowded with spicules. Most spicules are small and stellate (to 0.0375 mm diameter) with five to seven and sometimes nine blunt-tipped conical or short almost rod-like rays in optical transverse section. Also occasional large spicules to 0.7 mm diameter with four to six long spiky rays are present. Long branched stolonic vessels extend from the zooids into the base of the colony.

Zooids are small, lack an atrial tongue and have a narrow thorax. A long oesophageal neck has a fine, tapering retractor muscle projecting from halfway down. Buds on long stalks projecting from the base of the oesophageal neck. A wide, shallow, cup-shaped lateral organ projects from each side of the thorax, opposite the third and fourth rows of stigmata. The newly recorded colonies are in vegetative phase, and neither gonads nor larvae are present.

Remarks. The small sessile colonies are similar to those of Didemnum fraternum ( Sluiter, 1909) and D. turritum Michaelsen, 1930 , both of which have two groups of stellate spicules, mostly smaller ones to 0.05 mm diameter and a few larger spiky ones as in the present species. Further, the newly recorded material is from Shark Bay, the type locality of D. turritum . Nevertheless, syntypes of the latter species (ZMH T1701) have more rays, and more sharply pointed spicules, and the species appears to be a synonym of D. membranaceum (see Kott, in press).

Kott (2001) was mistaken in thinking that the present species was a synonym of Diplosomoides cuculliferum Sluiter, 1909 , which now is known to be a species of Polysyncraton (see Kott, in press). Didemnum algasedens Monniot and Monniot, 2001 also has similar zooids and colonies and the same number of vas deferens coils as the present species. However, it has more, and more sharply pointed, spicule rays and lacks the giant spiky spicules of the present species.

Figures

FIG. 13. Didemnum nekozita (WAM 15.93): (A) colony; (B) vertical section through colony; (C) spicules. Scales: (A) 5.0 mm; (B) 0.2 mm.