Sycozoa cavernosa Kott, 1990

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 : 1962-1963

Sycozoa cavernosa Kott, 1990

Sycozoa cavernosa Kott 1990, p. 142 .

Distribution

Previously recorded ( Kott 1990): western Australia (various locations from the Dampier Archipelago to Cockburn Sound), New record: CSIRO 05 / 07 western Australia (Station 171-005, Kulumburu, 13.05 S 124.02 E, 100 m, 16.5.07, QM G328556 ) .

Description

The specimen has a cone-shaped head of the usual form supported on a thin stalk with basal rootlets. The terminal surface of the head is flat and circular in outline, with a central common cloacal aperture. The head reduces in diameter toward the stalk. Zooids are arranged in double rows that extend the length of the head. Narrow connectives cross the extensive common cloacal cavity that separates the outer zooid-bearing layer of test from a central core. Vegetative stolons from each of the zooids extend, parallel to each other, through the connectives, into the central test mass and down into the stalk. The stolons from each of a pair of zooids occupy a single connective. Zooids open into the large common cloacal cavity by a sessile, transverse opening that exposes a large part of its branchial sac and that sometimes has its anterior rim produced into a large lip. The zooids are relatively small. The branchial sac has the usual two pairs of rows of stigmata, the pairs being separated ventrally (where the stigmata are reduced in length) by an unperforated triangle of the pharyngeal wall. The stomach is relatively small, smooth and almost fusiform. Gonads were not detected in this specimen, but previously have been reported in a sac constricted off from the posterior end of the abdomen ( Kott 1990).

Remarks

The species is remarkable in having an extensive common cloacal cavity in which the longitudinal canals usually found in this genus are expanded into large spaces crossed by connecting strands of test that connect the surface layer of test to a central core. The vegetative stolons of each pair of zooids extend through the connecting strands into the internal test core and down into the stalk of the colony. In the holotype ( Kott 1990; fig. 52) the terminal common cloacal cavity appears to be large, occupying the whole head of the colony, although the ridges of test (in which the zooids are embedded) between the cloacal canals persist and have not been reduced to the strands found in the present specimen. The present specimen also differs from the holotype in its long narrow stalk that resembles that of the Antarctic S. sigillinoides . In addition to the expanded common cloacal cavity, the present species has, like S. sigillinoides , a single central common cloacal aperture in the terminal free end of the head. However, the Antarctic species has more numerous stigmata in each half row (16–26) and the colony head is more oval than the conical head of the present species.

The newly recorded specimen from 100 m is the greatest depth yet recorded for the species, which is known only from western Australian from Cockburn Sound to the north-western coast. It is possible that its usual habitat is from deeper waters and that the few available records and its apparently limited geographic range may be the result of the lack of sampling in these deeper waters.