Molgula elva, Kott, 2008

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 : 1209-1213

Molgula elva sp. nov.

( Figures 15F, G )

Distribution

Type locality: Western Australia CSIRO SS10 / 05 (Abrolhos, Stn 091, 113.7840E 28.9888S, 180 m, 3 December 2005, holotype WAM Z27525 ) .

Description

The only available specimen (the holotype) is small, laterally flattened and covered with a layer of sand adhering to delicate hair-like test processes. The apertures are sessile, relatively close together at the end of a slightly oval body about 1 cm long. The body wall is delicate and transparent with fine longitudinal muscle bands radiating from each of the apertures, just reaching those of the other aperture in the middle of each side but extending only halfway down each side of the body. Circular muscles are around each aperture. The longitudinal body muscles insert into six well-spaced pointed processes around each of the apertures. The branchial tentacles have sparse primary and secondary branches but only minute tertiary ones and are not bushy. The small dorsal tubercle tightly enclosed in the peritubercular V has a simple pit-like opening. The dorsal lamina is a plain-edged single membrane. Six branchial folds are on each side of the body. Each fold has about four fine longitudinal vessels along its ventral side but only one, near the edge of the fold, is on the dorsal side. Two long stigmata spiral together around each of the six infundibulae that extend in a row in each of the branchial folds. The gut forms a narrow, slightly curved loop around the postero-ventral curve of the body, close to the endostyle. It has a relatively long oesophagus, a short stomach divided into four longitudinal chambers and a few elongate glandular pockets at the distal end of the stomach. The smooth-edged anal opening is about halfway along the oesophagus. On the right side of the body the long oval kidney is in a position corresponding to that of the stomach on the left. A gonad extends along close and parallel to the curve of the gut loop on the left and the dorsal side of the kidney on the right. Each gonad consists of a fringe of long branched testis follicles along the posterior margin of the long axis of the tubular ovary. The long axes of the testis follicles are at right angles to the long axis of the ovary. The oviducal opening is at the distal end of the ovary, directed toward the atrial aperture but distant from it. Vasa efferentia join to a single vas deferens on the surface of the ovary. The distal end of the vas deferens projects free of the body wall from the anterior margin of the ovary near the base of the short oviduct and is directed toward the atrial aperture. In the present specimen the eggs appear to be mature but the testis and male ducts are not fully developed. The species is likely to be protogynous.

Remarks

The gonads and their position on the body wall are similar to those of the temperate and sub-antarctic Molgula malvinensis and M. rima , although in those species the gonads are longer, extending further anteriorly than in the present species, tending to curve around the anterior end of the kidney and the gut loop, respectively. The velum said to be at the base of the branchial siphon in the latter species was not detected in the present specimen.

Other species of Molgula generally encountered in Australian waters have the male follicles at the proximal end of the ovary, or, in those species in which the male follicles tend to encircle the ovarian tube, they often have multiple openings of the vas deferens rather than the single opening found in the present species. The fourchambered stomach and the gently curved arc of the gut loop are also unusual in this genus where glandular folds and pockets in the pyloric region are usually more elaborate and the gut loop more deeply curved.

Figures

Figure 15. Cnemidocarpa completa (QM G328141): A, external view; B, internal view, right side showing branchial sac cut away to display gonads. Stolonica aluta (QM G328460): C, external view of a single zooid; D, pallial wall showing gut and gonads on left side. Pyura scortea (QM G328138): E, external view. Molgula elva sp.nov. (WAM Z27525): F, detail of branchial infundibula; G, internal view showing body organs and muscualture. Scales: A, E, 0.5 cm; B–D, 0.2 cm; F, 0.5 mm; G, 1 mm.