Trididemnum sibogae (Hartmeyer, 1910)

Kott, Patricia, 2008, Ascidiacea (Tunicata) from deep waters of the continental shelf of Western Australia, Journal of Natural History 42 (15 - 16), pp. 1103-1217 : 1193-1194

Trididemnum sibogae (Hartmeyer, 1910)

( Figure 19B )

Didemnum sibogae Hartmeyer 1910, p1489 (nom. nov. for D. ramosum Sluiter 1909, p. 63 ). Kott 2005a, p. 2458 and synonymy.

Distribution

Previously recorded (see Kott 2005): circum Australia; New Caledonia: India. New record: Western Australia CSIRO SS10/05 (Bald I., Stn 35, 157 m, 24.11.05, QM G328009).

The new record confirms the presence of this tropical species in temperate

Australian waters.

Description

The colony is sheet-like, with an extensive horizontal posterior-abdominal common cloacal cavity, although in places it encrusts calcareous rubble and becomes irregular and more or less three-dimensional. The spicules are present throughout the colony. They are stellate, occasionally to 0.12 mm diameter with 9–11 strong conical pointed rays.

Remarks

The species is characterized principally by the number and form of the spicules, which are smaller than those of T. grandistellatum and T. titanium , with more spicule rays than either T. nobile or T. pusillum (which have only 7–9) and with fewer rays and less attenuated ray tips than T. pigmentatum .

Table, showing Trididemnum spp. with stellate spicules to 0.08 mm or more

The known Trididemnum spp. with stellate spicules up to 0.08 mm or more in diameter are set out in Table 1. They all have robust zooids. The colonies are variable but often three-dimensional and they may be affected by age and environmental factors including substrate. These species are readily confused with one another.

Figures

Figure 19. Scanning electron micrographs of didemnid spicules: A, Trididemnum grandistellatum, QM G328007; B, Trididemnum sibogae, QM G328421; C, Lissoclinum maculatum, QM G328462.