Aplidium magnilarvum Kott, 1992

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 : 1158-1159

Aplidium magnilarvum Kott, 1992

( Figures 9D–G )

Aplidium magnilarvum Kott 1992a, p. 563 .

Distribution

Previously recorded (see Kott 1992a): Western Australia (Eucla). New records: Western Australia CSIRO SS10/05 (Cape Mentelle, Stn 15, 21.11.05, 97 m, QM G328442, G328449 Albany, Stn 26, 212 m, 23.11.05, QM G328431; Bald I., Stn 39, 99 m, 24.11.05, QM G328101).

The species now is known from six specimens, all from off the southern coast of Western Australia in the western half of the Great Australian Bight at depths from 99 to 212 m. Previously recorded specimens are from 180 190 m ( Kott 1992a) .

Description

The newly recorded colonies are circular cushions to about 2–5 cm deep and 5–10 cm diameter to top- or fungus-shaped, the upper surface sometimes flat but sometimes raised into a dome. Sand is embedded in the surface test and around the sides and base of the colony but internally it is less crowded and occasionally is sparse. Both the top-shaped colony (QM G328431) and a cushion-shaped one (QM G328442) have the hard, rigid, sand-filled test round the side of the colony overlapping the outer margin of its convex upper surface. This may be an artefact caused by the collapse of the soft internal test while the stiff marginal test stands up around it. A particularly large circular cushion (QM G328449) about 10 cm diameter and 5 cm high has sand adhering to the outer wall and scattered throughout the colony although it is absent from the almost flat reddish jelly-like upper surface. The red colour results from the minute spheres throughout the test where they generally are obscured by the embedded sand. Evenly spaced common cloacal apertures sometimes are evident on the upper surface. In the large colony, which lacks sand in the upper surface, zooids can be seen to be in crowded circular systems around each of these relatively closely spaced fleshy common cloacal apertures. Internally, the long thread-like red zooids are very crowded. They are close and parallel to one another at the surface, although posteriorly they criss-cross one another in the internal test. Thoraces are long but relatively broad with about 15–20 rows of about 20 stigmata in each half-row. A short terminal branchial siphon has six lobes around the aperture and an atrial tongue of variable size with a bifid tip arising from the body wall just anterior to a small atrial siphon. A small stomach halfway down the descending limb of the gut loop has five folds. The posterior abdomen contains one and sometimes two rows of male follicles. A large translucent yellowish egg is at the proximal end of the posterior abdomen, and in some of the zooids the egg appears to have increased in size, become elliptical and is found at the top of the abdomen just behind the thorax. In some specimens the testis follicles are in single regular rows in the posterior abdomen but in other specimens regular or irregular double rows are present.

Remarks

Although the newly recorded colonies are different from the upright lobes of the type material, the disposition of the embedded sand, the form of the zooids and what appears to be a single large egg found at various levels, presumably moving up the abdomen to the atrial cavity, are the same. Zooids have a large atrial tongue separate from the small atrial siphon, and a small stomach with five longitudinal folds. The species has similar distribution of sand to that in Aplidium panis sp.nov. but the latter species has a clump of red vesicles associated with each zooid and sand is almost entirely absent from the internal test. Aplidium tuberosum also is also similar but has sand crowded throughout the test, especially in the centre of the colony, and its circular systems are separated from one another by depressions in the surface.

Present records suggest that the species could be endemic to the deeper waters of the Great Australian Bight.

Figures

Figure 9. Aplidium hyacinthum sp. nov. (QM G328108): A, colony; B, thorax and abdomen; C, part of posterior abdomen. - Aplidium magnilarvum (D, G, QM G328442; E, F, QM G328101): D, colony; E, thorax and abdomen; F, anterior part of posterior abdomen showing large egg; G, larva Scales: A, D, 1.0 cm; B, C, E, F, 0.5 mm.