Corella aequabilis Sluiter, 1904

Kott, Patricia, 2009, Taxonomic revision of Ascidiacea (Tunicata) from the upper continental slope off north-western Australia, Journal of Natural History 43 (31 - 32), pp. 1947-1986 : 1971-1973

Corella aequabilis Sluiter, 1904

(Figure 2C)

Corella aequabilis Sluiter, 1904, p. 17 .

? Corynascidia sedens Sluiter 1904, p. 20 .

? Corynascidia alata Monniot C. and F. 1991, p. 383.

Distribution

Previously recorded: Indonesia, to 397 m. New record: CSIRO SS05 / 2007 western Australia (Stn 172-051, Kulumburu, 153.06 S 124.01 E, 105 m, Beam trawl, 16.5.07, QM G328560 ) .

Description

The preserved specimen is laterally flattened around the mid-dorsal and mid-ventral lines. It is almost rectangular, about 2.5 cm long and 2.0 cm wide with small papillae about 5 mm apart on the surface of the test. These papillae are terminally divided into three small points with side branches. The apertures, conspicuous and wide open in this specimen, are at opposite ends of the upper surface and are turned away from one another. They are on short siphons, which have circular muscle bands around them. The branchial aperture is at the anterior end of the ventral midline and the atrial aperture is about one third of the body length from it. The test is glassy and transparent, delicate on the right but thicker and lens-like on the left, and has no sand or other foreign particles adhering to it.

Apart from the circular siphonal muscles, muscles were not detected in the body wall of this specimen, which is relaxed. Long, pointed languets, flattened anteroposteriorly across their bases, lie along the dorsal midline of the long branchial sac. A small dorsal tubercle with a horseshoe-shaped slit (its open interval directed anteriorly) is in the dorsal midline behind a circle of simple tentacles at the anterior end of the dorsal lamina. About 80–100 crowded internal longitudinal vessels on each side extend parallel to one another along the length of the branchial sac, crossing the very numerous narrow transverse rows of small crowded infundibula. These are arranged in a regular row beneath each internal longitudinal vessel, each with only three coils of a stigma. The oesophagus is short and opens almost immediately into a pearshaped stomach that occupies about half of the proximal limb of the narrow gut loop that lies across the posterior end of the body to the right of the midline. The stomach has parallel, longitudinal, internal folds. The rectum continues up to the base of the atrial siphon as a straight tube more or less at right angles to the gut loop. The anal margin is divided into small, regular rounded lobes. Gonads are in the gut loop, spreading through it and around the adjacent walls of the intestine. The crowded branching tubules of the ovary are mainly around the duodenal part of the intestine (the distal half of the proximal limb of the gut loop) and the pole of the loop while the minute crowded white testis follicles are around the distal limb of the loop. However the ovarian tubes and testis follicle do mingle with one another. The vas deferens emerges from amongst the testis follicles on the outside of the gut loop and extends forward to the atrial aperture with the rectum.

Remarks

The present species is distinguished by its large branchial sac with numerous, regular transverse and longitudinal rows of small regularly arranged infundibula. Each of the longitudinal rows is associated with one of up to 100 crowded, parallel internal longitudinal branchial vessels that transverse the length of the branchial sac. The infundibula are always small, each containing a stigma that spirals only three times. The newly recorded specimen closely resembles the type specimen ( Sluiter 1904) and is about the same size with the apertures about one third of the body length apart. Although circular siphonal muscles are present in the newly recorded specimen, the weakly developed short transverse bands that Sluiter reported crossing the dorsal midline between the two siphons were not detected. This may be because they are fine and inconspicuous when not contracted.

Kott (1985) thought that the present species and C. japonica Herdman, 1880 ( Tokioka 1953, 1967; Millar 1975; Kott 1981) reported from 10–90 m off Japan, Hong Kong, China, Fiji and Zanzibar) could be conspecific. However, C. japonica has a smaller pharynx with not more than about 30 internal longitudinal vessels, the stigmata coiling up to five times in each infundibulum and it has hairs and other protuberances on the test. With the exception of the Japanese specimen from 174–201 m that Millar (1975) assigned to C. japonica (which is said to have transverse muscles from between the siphons extending onto the left side of body), the species is reported to have an irregular, open mesh of muscles on the left. Possibly as these muscles contract together they obscure the branching of the muscles bundles that form the open meshwork. Another species from Japan, C. asamusi Oka, 1927 , thought to be a subspecies of C. japonica , is characterized by a mesh of muscles over the whole of the left side of the body wall.

Corella eumyota Traustedt, 1882 , the commonly reported Corella species in southern temperate Australian waters, the South Pacific and Macquarie Is., is distinguished from the present species by its mesh of muscles on the left side of the body, irregular branchial sac with interstitial infundibula, up to a maximum of only about 27 internal longitudinal vessels with three associated with each longitudinal row of infundibula and more numerous coils in each of the stigma.

Corynascidia alata Monniot C. and F., 1991 from New Caledonia is possibly conspecific with the sessile species C. sedens Sluiter, 1904 from Indonesia despite the problematic large “aliform” organ of unknown homology near the atrial opening; and some ciliated epithelium detected in parts of the branchial sac in C. alata . Both these species having a small dorsal tubercle, pointed dorsal languets and short transverse muscle fibres crossing the dorsal midline between the two siphons; and both differ from the present species in the large square branchial meshes, each with about five coils of the stigma.