Trididemnum sibogae ( Hartmeyer, 1910 )

Kott, Patricia, 2007, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 4), Journal of Natural History 41 (17 - 20), pp. 1163-1211 : 1203

Trididemnum sibogae ( Hartmeyer, 1910)

( Figure 11B ) Didemnum sibogae Hartmeyer 1910, p 1489 (nom. nov. for Didemnum ramosum Sluiter

1909, p 63); Kott 2001 part (see below), p 283 and synonymy; 2004b, p 2505; 2005a,

p 2458 and synonymy. Not Kott 2001, p 283 from: Westernport, QM G300955 (2001,

Figure 132A) and QM G300971 (2001, Plate 17B); Kingston, QM G302875 (2001,

Plate 17F); and Port Davey (Tasmania) QM G3028845 Trididemnum titanium sp. nov.

Distribution

Previously recorded (see Kott 2005a): Western Australia (Cape Jaubert) ; South Australia (Cape Jaffa ; Victoria (Western Port); Tasmania ( Port Davey ) ; New South Wales (Port Hacking, Port Jackson, Arrawarra ); Queensland (Fraser I., Bargara, Cairns, Princess Charlotte Bay ) ; Northern Territory (Darwin, Gulf of Carpentaria); West Pacific ; Indian Ocean. New records : Queensland ( Great Barrier Reef : 17.865 ° S, 146.645 ° E, 66 m, QM G308844 ; 17.645 ° S, 146.375 ° E, 27 m, QM G308898 : 18.015 ° S, 146.295 ° E, 25 m, QM G308893 ; 18.615 ° S, 146.645 ° E, 30.5 m, QM G308841 ) .

The species has a wide Indo-West Pacific tropical range, and is around the southeastern corner of Australia (including Tasmania), where it is sympatric with T. titanium sp. nov.

Description

Colonies are complex, with cylindrical projections from the surface overgrowing and joining with other parts of the colony surface to form a three-dimensional trabeculum enclosing external spaces within the colony. These enclosed spaces (which maintain their connection to the external environment through gaps of various sizes and shapes), together with the extensive posterior abdominal common cloacal cavities, result in a spongy colony. Stellate spicules with 11–13 long attenuated pointed rays are present throughout although they are most crowded at the surface. The rays are conical, their base spread out to form an obtuse angle with adjacent rays.

Zooids are relatively small with a large branchial siphon and the incurrent fringed with six short, pointed lobes. The atrial siphon is posteriorly directed. A fine retractor muscle of variable length projects from the posterior end of the thorax. Eight coils of the vas deferens surround the undivided testis.

Remarks

The present damaged specimens have been identified by their three-dimensional colonies and the spicules, which are distinguished from the spicules of T. pigmentatum by their smaller size, not exceeding 0.1 mm diameter, and spicule rays, which are wider basally than the long and narrow attenuated, crowded spicule rays of T. pigmentatum . The temperate Australian species T. amiculum Kott, 2001 has similar colonies and the spicules are the same size, but the rays are relatively shorter and stumpier, and there are only seven coils of the vas deferens. The tropical T. lapidosum Kott, 2001 has larger spicules, also with more stumpy rays than those of the present species. Trididemnum pusillum Kott, 2004a from northwestern Australia has similar spicules although their distribution is different and the colonies are fleshy plates unlike the three-dimensional trabeculae of the present species. The species has been confused with T. titanium sp. nov. Its distinctions from that species are discussed below.

Figures

Figure 11. Scanning electron micrographs. (A) Trididemnum pigmentatum (QMG308842); (B) Trididemnum sibogae (QM G308893); (C) Trididemnum titanium (QM G308816); (D) Lissoclinum capsulatum (QM G308804); (E) Lissoclinum reginum (QM G308871); (F) Didemnidae?genus?species (QM G308889); (G, H) Didemnidae?genus?species [(G) QM G308888; (H) QM G308900].