Didemnum stragulum Kott, 2001

Kott, Patricia, 2005, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (Part 3), Journal of Natural History 39 (26), pp. 2409-2479 : 2452

Didemnum stragulum Kott, 2001

( Figure 16E )

Didemnum stragulum Kott 2001, p 238 and synonymy;?2004a, p 760.

Distribution

Previously recorded (see Kott 2001): Western Australia (?Montebello Is); Queensland (Heron I.); Indonesia; New Caledonia; eastern Indian Ocean (Cocos Keeling Is). New record: Western Australia (NW Long I., Passage Is, WAM 162.93).

Description

The newly recorded colony is hard, encrusting weed. The surface appears to be a mosaic of slightly elevated, irregular, whitish, zooid-free patches, separated from one another by slight surface depressions (over the common cloacal canals) that appear grey owing to the lack of spicules in the surface test, and the discontinuity in the depth of spicules owing to their interruption by the canals. Zooids are along each side of these canals, their ventral surfaces in the zooid-free stands of test surrounded by the canals. The spicules are characteristically variable in size, the smaller ones mixed with the larger ones (to 0.1 mm). Spicules have 9– 11 long, sharply pointed rays in optical transverse section, with the rays sometimes varying slightly in length.

Remarks

The newly recorded material lacks the surface papillae associated with each branchial aperture that is so conspicuous in the type material. Nevertheless, the colony otherwise resembles those previously described. The mixture of small and large spicules appears to be characteristic of this species. It has a wide recorded range in the tropical waters of the Indo-West Pacific.

Figures

Figure 16. Scanning electron micrographs of the calcareous spicules of: (A) Didemnum incanum (SAM E3238); (B) Didemnum leopardus sp. nov. (QM G308719, holotype); (C) Didemnum moseleyi (WAM 175.93); (D) Didemnum plebeium sp. nov. (WAM 155.93, syntypes); (E) Didemnum stragulum (WAM 162.93); (F) Didemnum ternerratum (SAM E3240); (G) Trididemnum amiculum (SAM E3263); (H) Trididemnum areolatum (QM G308746).