Aplidium formosum, Kott, 2006

Kott, Patricia, 2006, Observations on non-didemnid ascidians from Australian waters (1), Journal of Natural History 40 (3 - 4), pp. 169-234 : 205-207

Aplidium formosum sp. nov.

( Figure 6A–E )

Distribution

Type locality. South Australia ( Port Adelaide , pylon 3, 3 m, holotype SAM E2899 ) .

Description

The holotype is a wedge-shaped gelatinous colony to 2 cm high, with the upper surface partially divided into lobes. It is pinkish in preservative although the colour (which is caused by pigment in the body wall of the zooids) fades to colourless and translucent towards the base of the colony. The Aplidium colony mingles with, and possibly is being overgrown by, a colony of Botrylloides leachii . Small, crowded, thread-like zooids open on to the flat surface of the Aplidium colony. Their arrangement is obscure. They have a short six-lobed branchial aperture and an antero-dorsal atrial aperture with a pointed tongue from the anterior rim of the opening. Eight rows of relatively long rectangular stigmata are in the branchial sac. The gut loop is about the same length as the thorax. The stomach has 16 parallel folds. A large ovary with up to seven eggs is at the top of the long posterior abdomen anterior to the double row of testis follicles. Up to eight embryos are in a developmental sequence in the narrow atrial cavity, the most advanced at the top near the atrial aperture.

The larval trunk (to 0.4 mm long) is almost cylindrical and the tail is wound around it about two-thirds of the way. The larval pharynx has two rows, each of about eight stigmata per side and the gut forms a horizontal loop behind the pharynx. About six epidermal vesicles project from small conical median ampullae that alternate with the adhesive organs but regress and disappear as the vesicles separate from them. Patches of about six vesicles are also suspended in the larval test in the median line behind the upper and the lower adhesive organs, respectively.

Remarks

The zooids of the present species are shorter than the thread-like zooids of many Aplidium spp. but the stigmata are relatively long. The zooids of the present species resemble those of Aplidium rosarium Kott, 1992a , having similar numbers of stigmata in a similar number of rows, its larvae lined up in the atrial cavity and clumps of antero-median vesicles in the larval test alternating with the adhesive organs. However, A. rosarium also has lateral larval vesicles, which are not in the larvae of the present species.

Figures

Figure 6. (A–E) Aplidium formosum (holotype SAM E2899): (A) colony; (B) thorax, abdomen, and proximal part of posterior abdomen, showing ovary; (C) posterior abdomen showing male follicles; (D, E) larvae. (F, G) Aplidium laticum (syntype QM G308832): (F) thorax and abdomen; (G) posterior abdomen. Scale bars: 1 cm (A); 0.2 mm (B, C, F, G); 0.1 mm (D, E).