Trididemnum dispersum ( Sluiter, 1909 )

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 : 2455-2456

Trididemnum dispersum ( Sluiter, 1909)

( Figure 17A )

Didemnum dispersum Sluiter 1909, p 54 .

Trididemnum dispersum Kott 2001, p 267 .

Distribution

Previously recorded (see Kott 2001): Western Australia (Shark Bay), Queensland (Capricorn Group); Northern Territory (South Ledge Reef); Indonesia. New record: Western Australia (Shark Bay, WAM 1044.89).

Description

The newly recorded colonies are small round cushions to 0.5 cm diameter. Spicules are evenly distributed in the surface test, except around the apertures where they are more crowded. They are less crowded in the remainder of the colony. A common cloacal aperture is in the centre of the upper surface and zooids appear to be in two series inside the outer margin of the colony. Terminal ampullae of vascular stolons are in the basal test around the outside of the colony. Plant cell symbionts are embedded in the test and are not in the common cloacal cavity. Zooids have a short atrial siphon from the posterior third of the dorsal surface.

Remarks

The zooids and colonies are generally smaller but otherwise similar to those previously described. The relatively few records for this species, which has a wide recorded geographical range, are, presumably, a result of its small, inconspicuous colonies.

Figures

Figure 17. Scanning electron micrographs of the calcareous spicules of: (A) Trididemnum dispersum (WAM 1044.89); (B) Trididemnum nobile (SAM E3262); (C) Trididemnum pigmentatum (QM G308714); (D) Lissoclinum agriculum sp. nov. (WAM 179.93, syntypes); (E) Lissoclinum bistratum (WAM 1018.89); (F) Lissoclinum clavatum sp. nov. (SAM E3260, holotype); (G) Lissoclinum coactum (WAM 120.90); (H) Lissoclinum diversum (WAM 153.86).