Didemnum moseleyi ( Herdman, 1886 )

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 : 1183

Didemnum moseleyi ( Herdman, 1886)

( Figures 14A ; 17H )

Leptoclinum moseleyi Herdman 1886, p. 272 .

Didemnum moseleyi: Kott 2007, p. 1186 and synonymy.

Distribution

Previously recorded (see Kott 2001, 2007): Western Australia (Shark Bay, Port Hedland, Houtman’s Abrolhos, Cockburn Sound; Queensland (Currumbin, Mackay, Capricorn Group Great Barrier Reef); Indonesia, Philippines, Palau, New Caledonia, Tokara Is, Indian Ocean. New record: Western Australia, CSIRO SS10/05 (Zuytdorp, Stn 104, 97 m, 05.12.05, QM G328455).

This is a tropical, Indo-West-Pacific species and the new record is well within its known range.

Description

The colony is a thin encrusting sheet, white in preservative, with circular common cloacal canals lined on each side by zooids. Spicules (to 0.05 mm diameter) are diverse and are crowded throughout the colony. They consist of stellate spicules with 11–13 conical but relatively blunt rays in optical transverse section and almost globular spicules with crowded flat tipped or rounded rays. A single larva found in the colony has a larval trunk to 0.65 mm long with the tail wound almost the whole way around it. Four lateral ampullae are along each side of the median adhesive organs and a small horizontal lateral ampulla is on the left behind the adhesive array. The adhesive organs are particularly small with narrow stalks and particularly narrow and shallow epidermal cups from which the cone of adhesive cells projects forward on a narrow neck. This could represent either an artefact or a developmental stage of these organs, although it has not previously been reported. Three rows of stigmata are in the larval pharynx although there are four rows in the adult zooids.

Remarks

Although the gonads are not present, the three rows of stigmata in the larval pharynx but four in the adult indicate that this is a Didemnum sp. The diverse but relatively small spicules of two different types are characteristic of the present widespread species.

Surprisingly, larvae for this species have not been reported often. Kott (1962) and Tokioka (1967) reported larvae with four pairs of lateral ampullae, although the larvae from specimens from Darwin ( Kott 2005a) have six ampullae on each side. It is possible that this character will be found to be a variable one, but at this stage the problem is not resolved. Didemnum ossium Kott, 2001 has both types of spicules but the stellate spicules have more rays, there are fewer globular spicules and many more larval lateral ampullae than the present species.

Figures

Figure 14. Didemnum moseleyi (QM G328455): A, larva. Didemnum multiampullae sp. nov. (QM G328057): B, larva. Didemnum tapetum sp. nov. (QM G328016): C, abdomen showing gut loop and testis; D, larva. Didemnum velum sp. nov. (QM G328120): E, zooid; F, thorax showing lateral organs. Trididemnum grandistellatum sp. nov. (QM G328007): G, thorax; H, abdomen. Scales: A–H, 0.2 mm.

Figure 17. Scanning electron micrographs of didemnid spicules: A, Polysyncraton millepore, QM G328050; B, Polysyncraton?palliolum, QM G328161; C, Polysyncraton pavimentum, QM G328058; D, Didemnum?candidum, QM G328457; E, Didemnum cygnuus, QM 328456; F, Didemnum dolium, QM G328008; G, Didemnum jedanense, QM G328005; H, Didemnum moseleyi, QM G328455.