Synoicum rapum, 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 : 1144

Synoicum rapum sp. nov.

( Figures 6E–G )

Distribution

Type locality: Western Australia CSIRO SS10 / 05 (Albany, Stn 22, 118.2940E 35.3350S, 99–100 m, 22 November 2005, holotype WAM Z27518 , QM G328012 ) .

Description

The holotype is a large, turnip-shaped colony about 9 cm high and 5 cm diameter across the upper (convex) surface. Colony diameter decreases toward the base. In places, zooids seem to be arranged in circles around tightly closed common cloacal apertures. However, generally, their arrangement is obscured by the tough, hard test which has a thin layer of sand externally. A layer of sand is present internally at the posterior end of the abdomen but is only sparse elsewhere. The test is a mulberry colour in preservative, the colour being especially conspicuous internally.

Zooids are long and thread-like. Both apertures are on conspicuous siphons. The long branchial siphon, with six pointed lobes around the rim of the opening, inclines away from the longitudinal axis of these contracted zooids. The atrial siphon projects antero-dorsally, forming an obtuse angle with the branchial siphon at the anterior end of the body. The anterior rim of the atrial opening is produced into a narrow tongue, bifid at the tip, and the posterior rim of the opening is produced out into a single point, these projections framing a gaping opening. Longitudinal thoracic muscles extend obliquely from the siphons to the endostyle and the posterior end of the thorax. A small pointed papillum is in the midline posterior to the base of the siphon. Stigmata are in rows of about 30 (anteriorly) to 20 (posteriorly) on each side. Dorsally, they are long and narrow perforations but are shorter ventrally. Transverse vessels, containing conspicuous transverse muscle fibres, have about 20 minute rounded papillae along their length. Each transverse vessel is expanded into a triangular languet across the mid-dorsal line.

The shield-shaped stomach, in the middle of the relatively short abdomen, has a mulberry-like wall, with regular rounded pouches. The long duodenal region is separated from the expanded posterior stomach by a short length of mid-intestine. A distal length of mid-intestine curves around in the pole of the gut loop before expanding into the rectum, which occupies the whole ascending limb of the loop. The posterior abdomen is long and thread-like with small testis follicles in a single or double row part of the way along its length. A one-egg ovary is anterior to the male follicles.

Remarks

The new species described here has the usual characters of Synoicum . It lacks the twisted gut of Polyclinum and Aplidiopsis . Unlike Polyclinum , it has a long posterior abdomen with strong longitudinal muscle bands and testis follicles in a double or single row. However, it also has a dorsal papillum behind the atrial aperture and branchial papillae on the transverse vessels that resemble those in Polyclinum . Previously these branchial papillae had not been reported for Synoicum , but their occurrence in the present species suggests that they could occur. Their value in assessing phylogenetic relationships within this family is in doubt and they no longer can be considered characteristic of Polyclinum . Similar papillae were not detected on the transverse vessels of re-examined specimens of Synoicum atopogaster Kott, 1963 , S. buccinum Kott, 1992a , S. citrum Kott, 1992a , S. durum Kott, 1992a , S. longistriatum Kott, 1992a , S. macroglossum ( Hartmeyer, 1919) , S. obscurum Kott, 1992a , and S. sphinctorum Kott, 2006 . They were found, however, on the transverse vessels of Synoicum intercedens ( Sluiter, 1909) , which, like the present species, has a pouched stomach wall, the anterior rim of the atrial opening produced into an anterior lip and the posterior rim produced into a range of lobes or a lip. Unlike the present species, S. intercedens has branched colonies, each branch with a terminal common cloacal aperture. Synoicum partitionis ( Monniot, 1987) , with pouches in the stomach wall and branched colonies, each branch with a terminal common cloacal aperture like S. intercedens , lacks the branchial papillae. Synoicum erectum Kott, 1992a and S. sacculum Kott, 1992a (both known from temperate waters) also have pouched stomach walls but lack branchial papillae. Both these species resemble the present one in having a number of circular systems, S. erectum colonies have similar mushroom-like lobes but a narrow branchial sac with only about eight stigmata per half row, and S. sacculum has a lobed surface and testis follicles bunched in the posterior abdomen (not in longitudinal series as in the present 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.