Condominium areolatum ( Kott, 1963 )

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 : 1123-1125

Condominium areolatum ( Kott, 1963)

( Figures 3A–D )

Placentela areolata Kott, 1963, p. 74 .

Condominium areolatum: Kott 1992a, p. 397 and synonymy.

Distribution

Previously recorded (see Kott 1992a): Western Australia (Cockburn Sound): South Australia (Great Australian Bight, Taylor I.); New South Wales (Lord Howe I.); Queensland (Great Barrier Reef, Mackay, Torres Strait); New Caledonia. New record: Western Australia CSIRO SS10/05 (Point D’ Entrecasteaux, Stn 18, 100 m, 21.11.05, QM G328441).

Description

The newly reported specimen conforms to those previously described, being three flat fan-shaped sandy lobes arising from a common base. Each lobe has a groove along each side of its terminal edge. The small anteriorly directed atrial siphons open into one of these grooves, and the recurved branchial siphons open into the groove on the opposite side of the edge of the fan. The relatively large zooids are in a single layer along the edge of the fan projecting down toward the base of the colony. Each separately opening siphon is six-lobed, although the recurved branchial siphon has four lobes on its outer edge and only two on the other (under) side. The thoracic body wall contains a fine, rather regular meshwork of longitudinal and transverse muscles. Wide bands of fine longitudinal muscles continue along each side of the abdomen and the posterior abdomen. Twenty-two rows of stigmata are in the branchial sac, with about 30 rectangular stigmata per side anteriorly, reducing in number toward the posterior end of the sac. Conspicuous triangular languets on each transverse vessel are in a line just to the left of the mid-dorsal line. The epithelium on these dorsal languets is raised into rounded papillae. Two large embryos are being incubated in the posterior end of the atrial cavity. The spherical stomach is about halfway down the abdomen. It is empty in these specimens and the internal wall has fine longitudinal grooves (presumably in the glandular epithelium) that seem to fade out posteriorly. The pointed posterior abdomen is about the same length as the abdomen. It has small bunched testis follicles throughout. The ovary, consisting of a few large eggs, is at the anterior end of the posterior abdomen. Only part of one reasonably advanced larva was detected. The trunk appears to have been about 1.2 mm long and almost spherical. At the posterior end there is an ocellus, what appear to be two otoliths and part of the thorax including the branchial aperture. A great mass of yolk occupies most of the trunk. At the anterior end a band of long, narrow median ampullae is interrupted by three stalked, tulip shaped, antero-median adhesive organs, each with a long cone of adhesive cells set in a deep, delicate, inflated epidermal cup with thin walls that appears to be formed of squamous epithelial cells. These antero-median elements of the larval trunk are obscured by a wide arc of epidermal vesicles along each side of the anterior end of the larva. The tail is relatively short for such a large larva not extending the full length of its ventral surface.

Remarks

The species is not common and although it now is known from a considerable geographic range, records represent only single colonies, or fragments of colonies from widely separated locations, although the colonies probably are hidden from collectors by the sand embedded in the surface test ( Kott 1992a). The fact that most of the colony is embedded in the substrate further conceals the colonies, only the rims of the fan shaped lobes (with both incurrent and excurrent apertures) being exposed.

With the exception of the tail, larval organs are described here for the first time. They appear to be unique in the profusion of epidermal vesicles around the anterior end of the trunk and in the tulip-shaped adhesive organs. Although epidermal vesicles are known to occur in many polyclinid larvae, they are seldom as crowded as they are in this larva. Similar larval epidermal vesicles are in the (possibly polycitorid) genus Brevicollis Kott, 1990a although in that species they arise from large rounded lateral ampullae along each side of the adhesive organs which have not been detected in the present species. Also, the adhesive organs of Brevicollis appear to be invaginated into the trunk rather than on short stalks as in the present species.

It is possible that the immature larvae of the present species Kott (1992a) described as being only 0.44 mm long are less mature developing embryos rather than the well-formed larva described above.

Figures

Figure 3. Condominium areolatum (QM G328441): A, thorax; B, abdomen; C, posterior abdomen; D, anterior end of larval trunk. Condominium floreum sp. nov (QM G328116): E, colony; F, thorax and abdomen; G, posterior abdomen showing ovary and testis; H, details of the anterior part of the thorax showing branchial tentacles, dorsal tubercle neural gland and ganglion and the anterior part of the branchial sac. Scales: A–C, F–G; 1.0 mm; D, H, 0.5 mm; E, 1.0 cm.