Aplidium solidum ( Herdman, 1899 )

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 : 1159-1161

Aplidium solidum ( Herdman, 1899)

( Figure 10D )

Psammaplidium solidum Herdman 1899, p. 85 ; Kott 1992a, p. 586 and synonymy.

Distribution

Previously recorded (see Kott 1990a): Western Australia (Dampier Archipelago); eastern Australia ( Jervis Bay and north to the Tropic of Capricorn). New records: Western Australia CSIRO SS10 / 05 (Bald I., Stn 35, 157 m, 22.11.05, QM G328064 ; Bald I., Stn 39, 99 m, 24.11.05, QM G328065 ; Kalbarri, Stn 102, 96– 98 m, 05.12.05, QM G328466 ) .

Description

Irregular, hard, rigid, sandy colonies, from small cushions to upright double-sided plates have flat-topped elevations about 0.5 cm diameter on the surface. The surface test is depressed over the circular common cloacal canals that surround the surface elevations. Random common cloacal apertures are at some junctions of the common cloacal canals. Sand is present internally but is not crowded. Branchial apertures have six pointed lobes. A short projecting atrial siphon has a small lip from its anterior rim. The branchial sac has 12 rows of stigmata with about 10 per row. The short stomach with five longitudinal folds is halfway down the long abdomen. The posterior abdomina are of varying length from short (with about eight large crowded testis follicles bunched behind the abdomen) to long and thread-like (with testis follicles in double rows). Up to three relatively small (to 0.06 mm trunk) larvae are in the posterior end of the atrial cavity. Larvae have many vesicles around the anterior end but ampullae were not detected. The stalk of the adhesive organs are basally expanded.

Remarks

The external appearance of this species is dominated by the sand contained in, and adhering to, the surface of the colonies. Zooids often are relatively short and narrow, the thorax, abdomen and posterior abdomen being about equal length with few large male follicles (to about six). However, the posterior abdomina sometimes are long. A small, muscular atrial siphon with its small, short lip (from the anterior rim of the opening) is located antero-dorsally. The larval trunk is characteristically small (0.5– 0.6 mm long). The larval adhesive organs of this and related species (see A. petrosum Kott, 1992a ) have the base of the stem expanded.

A specimen of Aplidium petrosum Kott, 1992a from the Spencer Gulf, South Australia, is erroneously assigned to the present species (see Kott, 1992a, p. 586). Aplidium petrosum is known only from southern Australia and is distinguished from A. solidum by its larger larvae with median ampullae. The species can be separated from those with zooids arranged around common cloacal apertures by its circular common cloacal canals and quilted surface similar to Aplidium tabascum Kott, 1992 which has similar zooids and larvae to the present species and also lacks median ampullae. However, it has less sand, larger larvae, and fewer stigmata than in the present species. Aplidium lenticulum has a similar larva but only one is incubated at a time. It has median larval ampullae, a longer posterior abdomen and less sand in the colony than the present species. Aplidium caelestis has similar sandy colonies but its common cloacal canals are elongate rather than circular as they are in the present species and it has longer zooids with a narrowed anterior.

Figures

Figure 10. Aplidium panis sp. nov. (QM G326115): A, colony outline; B, thorax and abdmen; C, posterior abdomen. Aplidium solidum (QM G328064): D, zooid with larvae being incubated. Scales: A, 1.0 cm; B–D, 0.5 mm.