Didemnum nambucciensis, Kott, 2004

Kott, Patricia, 2004, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part I), Journal of Natural History 38 (19), pp. 731-774 : 753-754

Didemnum nambucciensis sp. nov.

( figure 12 )

Distribution. Type locality: New South Wales (Nambucca Heads, 13 m, coll. J. Watson, 11 January 1972, holotype QM G10025; paratype QM G10026).

Description. Colonies are large encrusting sheets, white in preservative with spicules crowded in the surface test (above the thoracic common cloacal canals). The basal test varies in thickness, sometimes forming the central core of ridges or conical elevations. It is gelatinous with relatively sparse spicules, sometimes in clouds but sometimes evenly distributed. Zooid openings are along each side of a network of slight surface depressions over the primary circular common cloacal canals that surround zooid-free areas. Each stellate branchial aperture is lined with spicules and is emphasized by the blackish pigment in the siphonal lining. About nine spiculefilled radial ribs are in the roof of the common cloacal cavity around each sessile common cloacal aperture. The common cloacal apertures are randomly distributed, and not always terminal. Spicules sometimes are stellate, to 0.05 mm diameter, with 17–19 crowded but slightly uneven conical rays; and others are globular with flat-tipped to rounded rays.

Zooids are a dark brownish colour, even after 25 years in preservative. They are small, with a relatively long cylindrical branchial siphon, a sessile, open atrial aperture with a pointed or rounded atrial tongue. A very long, tapering retractor muscle projects from the upper part of the oesophageal neck. The narrow thorax has about eight long narrow stigmata in the anterior row, but fewer in the other rows. Seven vas deferens coils are around the undivided testis. Larvae are not known.

Remarks. The spicules resemble those of Didemnum chartaceum Sluiter, 1909 , although they are smaller. However, the present species lacks the conspicuous bladder cells and spongy texture of D. chartaceum , has a thicker colony, spicules crowded throughout the upper layer of test and also in the lower half of the colony (rather than being only in single layers at the surface and on the base) and nine coils of the vas deferens. Didemnum multispirale Kott, 2001 also has spicules that resemble those of the present species but they are larger and it has more coils of the vas deferens. Didemnum elongatum Sluiter, 1909 , D. moseleyi ( Herdman, 1886) and D. poecilomorpha Monniot and Monniot, 1996 have stellate and globular spicules but fewer spicule rays than the present species.

Figures

FIG. 12. Didemnum nambucciensis (QM G10026): (A) thorax; (B) abdomen; (C) spicules. Scales: (A, B) 0.1 mm.