Eucoelium orientalis (Kott, 1990)

Kott, Patricia, 2006, Observations on non-didemnid ascidians from Australian waters (1), Journal of Natural History 40 (3 - 4), pp. 169-234 : 189-190

Eucoelium orientalis (Kott, 1990)

Polycitorella orientalis Kott 1990a, p 187 and synonymy; not E. orientalis: Kott 2003 .

Distribution

Previously recorded (see Kott 1990a): Western Australia (Rottnest I., Houtman’s Abrolhos); Queensland (Swain Reefs, Heron I., Coral Sea). New records: Tasmanian Canyons ( Banks Strait , 168 m).

Description

Colonies are dome-shaped to stalked, with a single layer of moderately crowded spicules in the surface over an aspiculate layer of variable thickness. Spicules also are present internally in varying concentrations. Spicules are to 0.05 mm diameter with 5–13 stout conical rays in optical section. Large zooids open around the upper domed surface and converge toward the centre of the base of the colony. They are in a vegetative state, the abdomina breaking up into replicates.

Remarks

Eucoelium is known, from only eight species, from Japan, the Gulf of Suez and the western Indian Ocean, New Zealand, and tropical and temperate waters around the Australian continent (where three species are known). The present species has been recorded from the Great Barrier Reef and the Coral Sea, but the present record implies a wider range into temperate waters. All the known species of Eucoelium are very variable, but can be distinguished by their spicules, those of the present species being to 0.05 mm diameter with 5–15 rays. Eucoelium mariae ( Michaelsen, 1924) from New Zealand has smaller spicules than the present species and the principally temperate E. coronaria Monniot, 1988 has larger spicules and its zooids are arranged in conspicuous circular systems. Eucoelium orientalis: Kott 2003 has large (to 0.09 mm diameter) globular spicules as well as smaller stellate ones and appears not to be a synonym of the present species.

This genus and another polycitorid genus, Cystodytes , are the only aplousobranch genera outside the Didemnidae with the capacity to create calcareous spicules in the test. Although the spicules are very similar to those of the Didemnidae , a phylogenetic relationship is not implied.

Like other species taken from the Tasmanian Canyons, the new record of the present species from so much further south than it was previously known provides further evidence that the Australian continent may constitutes a route for gene flow of shallow-water tropical species into temperate waters.