Synoicum pseudogrisiatum, 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 : 1141-1143

Synoicum pseudogrisiatum sp. nov.

( Figures 6A–D )

Distribution

Type locality: Western Australia CSIRO SS10 / 05 (Albany, Stn 22, 118.2940E 35.3350S, 100 m, 22 November 2005, holotype WAM Z27511, QM G328118 ; paratype QM G328123 ; further specimens; Jurien Bay, Stn 83, 113 m, 02.12.05, QM G328148 ) .

Description

The holotype (QM G328118) colony is a spherical, sandy ball about 5 cm in diameter and is fixed to the substrate by irregular but small holdfasts from a limited part of the lower surface. The paratype is three sandy lobes, narrowing to a common basal stalk. Each lobe is from 2 to 8 cm in diameter across the upper, more or less horizontal surface and up to 10 cm high. Some sand is embedded in the internal translucent test, but sand is crowded in the surface test. Two or three large systems open on the upper surface of each lobe. The systems are readily distinguished by the darker brownish-red colour of the zooids where they come to the surface around the deeply indented margin of a large circular elevated area with the large, sessile, common cloacal aperture in the centre. The indentations around the margin of this elevated area divide it into six or seven petal-shaped lobes, and the indentations which are associated with the depressions in the surface may be where common cloacal canals converge to a large common cloacal aperture.

Zooids are long and narrow, the branchial siphon is conspicuous with a prominent sphincter muscle and long branchial tentacles originating at different levels in the siphon and projecting back toward the lumen of the pharynx. A long, sometimes bifid atrial lip projects from the body wall some distance in front of the short atrial siphon. In some of the preserved material, the distended body wall forms a long S-shaped curve with the atrial tongue. In other specimens, the tongue lies flat against the anterior wall of the thorax. A conspicuous dorsal ganglion and gland (ventral to the ganglion) with a funnel-shaped neural duct opening into the pharynx can be seen at the anterior end of the mid-dorsal line of the thorax. Dorsal languets are at the dorsal end of the inter-stigmatal vessels as usual, although the anterior languet, just posterior to the dorsal neural complex, is particularly large. Stigmata are in about 20 short rows with about 12 in each half-row, leaving an imperforate strip of pharyngeal wall on each side of the middorsal line.

The abdomen contains a long, narrow gut loop. The stomach is relatively long and narrow, halfway down the abdomen. Sometimes it appears to have shallow folds. However, on careful examination these apparent folds are seen to be the result of the stretching and collapse of the stomach. The mesial wall of the stomach curves around the rectum, a cross-section of the stomach appearing as a crescent with its horns on opposite sides of the rectum and the suture line in the centre of the outer convex curve. Often, the lateral walls of the stomach collapse in to form two apparent folds each side of the suture line. In fact the stomach wall in these specimens is smooth and is not folded. In the absence of true structural folds (which would give strength to the stomach wall), compression of the stomach by contraction of the longitudinal muscles in the body wall produces some irregular transverse folds that obscure the shape of the stomach.

The testis follicles are in two short rows at the posterior end of the long posterior abdomen. A long vas deferens, convoluted as a result of contraction, extends forward to the thorax. An ovary was not detected.

Remarks

Both colonies and zooids of these specimens closely resemble Aplidium grisiatum Kott, 1998 (nom. nov. for A. griseum Kott, 1992a ) although the latter species has seven well-defined stomach folds. A close relationship may exist between A. clivosum (with five stomach folds) and A. grisiatum (with seven stomach folds) although their colonies are distinctive (see Kott 1992a) and a similarity between A. clivosum and the present species is not implied. Specimens of A. grisiatum from Darwin, the southern part of the Great Barrier Reef and the Palau Is. were free of sand externally and internally, sand being confined to the stalk section (see Kott 2002). As in the present species, the thorax is narrow and gonads are in the posterior part of the posterior abdomen. Nevertheless, there are eight stomach folds (seven in some newly examined colonies) and the species appears to be correctly assigned to Aplidium . The present newly recorded species from Western Australia, distinguished from A. grisiatum by its smooth stomach wall, is assigned to the genus Synoicum .

The thoraces of the present species resemble those of A. grisiatum , although they are larger and the atrial lips larger and more distinctly separated from the atrial siphon by a greater interval of the body wall. The atrial siphons and lip of the present species are similar to those of Synoicum macroglossum ( Hartmeyer, 1919) and S. papilliferum ( Michaelsen, 1930) rather than the majority of Synoicum spp. (which have an atrial lip projecting from the anterior rim of the aperture). The former species (see Kott 1990a) has long branched cloacal systems and is naked on the upper surface. Michaelsen (1930) was not able to detect the common cloacal apertures in the type specimens of S. papilliferum . These are conspicuous in the present species and distinguish it from Michaelsen’s species.

Figures

Figure 6. Synoicum pseudogrisiatum sp. nov. (QM G328118): A, colony; B, thorax and abdomen; C, posterior abdomen; D, anterior part of pharynx showing neural complex. Synoicum rapum sp. nov. (QM G328012): E, colony; F, thorax; G, part of branchial sac showing branchial papillae on transverse vessels. Scales: A, E, 2.0 cm; B–D, F, 1.0 mm.