Diplosoma fecundum, Kott, 2010

Kott, Patricia, 2010, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 2), Journal of Natural History 38 (26), pp. 2455-2526 : 2515-2525

Diplosoma fecundum sp. nov.

( figure 14 )

Distribution. Type locality: South Australia (Kangaroo I., Kingscote Jetty on piles, 3–4 m, coll. K. Gowlett Holmes, 3 May 1999, holotype SAM E2919).

Description. The soft translucent test is easily torn, and the colonies are grey owing to the black squamous epithelium that surrounds each zooid. Rounded ridges and deep furrows are on the surface of the colony, and white corpuscles in the test are gathered into small clumps that look like patches of spicules. The vast common cloacal cavity surrounds clumps of one to five zooids, each clump connected to the basal test by a single short basal connective. The common cloacal cavity penetrates around the zooids in each clump. Both surface and basal layers of test are thin. Zooids are of the usual form for this genus, with short branchial siphons, short retractor muscles and straight vas deferens. The testis is divided into two follicles.

Embryos are in a pouch projecting from the abdomen into the common cloacal cavity and this pouch remains attached to the abdomen as the larva is incubated. The larval trunk is about 1.1 mm long and the tail extends only halfway around it. Yellowish white corpuscles are in the larval test (as in the colony test) and are especially crowded in the posterior half of the trunk. Six ectodermal ampullae are on each side of the adhesive organs at the anterior end of the larva and these have conspicuous conical terminal caps of modified epithelial cells. Three crowded thoracic buds are on the left and three abdominal buds on the right. Zooids are in an active vegetative condition at the same time as the larvae are being incubated in the abdominal pouches.

Remarks. The species is like D. velatum Kott, 2001 , which has unbranched and sometimes relatively short test connectives anchoring clumps of zooids to the basal test. Larvae of D. velatum have only three pairs of lateral ampullae on each side of the median adhesive organs (see Kott, 2004: figure 22B), in the same work she recorded four pairs of lateral ampullae, but her description is incorrect. The tropical Diplosoma translucidum (Hartmeyer, 1909) also has similar common cloacal systems and two testis follicles like the present species. However, neither D. translucidum nor D. velatum has the black squamous epithelial tissue surrounding the zooids in the present species. The most conspicuous distinguishing characters are in the larvae, the present species having significantly more numerous blastozooids and more lateral ampullae.

Diplosoma ferrugeum Kott, 2001 has similar corpuscles in the colonial and larval test as in the present species, and the larvae develop in a similar brood pouch attached to the parental abdomen. However, D. ferrugeum larvae have fewer blastozooids and lateral ampullae than the present species. Diplosoma listerianum (Milne Edwards, 1841) , which also has black squamous epithelium, is distinguished from the present species by its branched basal test connectives and its larvae.

Diplosoma ferrugeum Kott, 2001

Diplosoma ferrugeum Kott, 2001: 337 and synonymy.

Distribution. Previous records (see Kott, 2001): Western Australia (Montebello Is, Houtman’s Abrolhos), New South Wales (Lord Howe I.), Queensland (Capricorn Group, Swain Reefs, Townsville, Lizard I.), Philippines. New record: Northern Territory (Rocky Reef, Darwin, QM G308663).

Description. The colony is the usual encrusting sheet with the characteristic brown-orange grey pattern in life. In preservative black pigment cells are in the

test interrupted by white opaque strips and flecks of crowded morula cells that also encapsulate the abdomen. Zooids are covered with black squamous epithelium and are contained in branching sheaths of test that cross the vast common cloacal cavity.

Remarks. The morula cells that characterize this species do not dissolve in acid and are not spicules. Lissoclinum laneum (see above) has similar bodies in the test.

Diplosoma translucidum (Hartmeyer, 1909)

Leptoclinum translucidum Hartmeyer, 1909: 1490 nom. nov. for L. perspicuum Sluiter, 1909 .

Diplosoma translucidum: Kott, 2001: 343 ; 2002c: 43.

Distribution. Previously recorded (see Kott, 2001, 2002c): Western Australia (Dampier Archipelago, Cape Ruthiers, Cape Jaubert), Queensland (Hervey Bay, Capricorn Group, Lizard I.), Northern Territory (Darwin); Indonesia, New Caledonia. New record: Northern Territory (East Arm, Old Man Rock, Darwin).

Description. Sheet-like investing aspiculate colony encrusting bryozoans. Zooids evenly distributed in clumps at the surface, each clump attached to the basal test by a connective that branches at the top to separate the zooids from one another. In life the colony appears to have been bluish beige, the zooid clumps apparent from the surface surrounded by the bluish colour where the deep common cloacal cavity separates them from one another.

Remarks. The differences between the present species and other Diplosoma spp. are discussed above (see D. fecundum ).

Figures

FIG. 14. Diplosoma fecundum (SAM E2919). (A) Colony surface showing ridges; (B) zooid; (C) larva. Scale bars: 1.0 cm (A); 0.1 mm (B); 0.2 mm (C).