Sycozoa Lesson, 1832

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 259-261

Genus Sycozoa Lesson, 1832

Sycozoa cerebriformis ( Quoy & Gaimard, 1834) ( Fig. 46 )

Aplidie cerebriforme Quoy & Gaimard, 1834: 625 , pl. 92, figs 16; 17. Type locality: Australia western Port ( MNHN A3 SYC. A 29 ) .

Sycozoa cerebriformis – Hartmeyer 1919: 121. — Brewin 1953: 58, and synonymy. — Kott 1957a: 99; 1972b: 8; 1972c: 170; 1976: 57. — Millar 1963: 708; 1966: 365. — Kott 1990: 143.

Sycozoa seiziwadai Tokioka, 1952: 99 . — Kott 1990: 152.

MATERIAL EXAMINED. — Indonesia. Komodo Island, Padar Kecil, Drop-off 7-15 m, coll. Erhardt ( MNHN A3 SYC 31).

DESCRIPTION

Colonies at the same station have various sizes and colours. They form simple or multiple fanlike lobes a top peduncles of ovoid or round section. The flattened lobes contain the zooids. The peduncles sometimes branch at mid-length. The peduncles are about 2 cm long and the heads 1.5 cm long. A lobe has several double rows of oral openings on the sides and the common cloacal openings of those systems at the top.

There are 10 to 12 functional zooids in a row, as in the holotype. The colonies are dioecious ( Fig. 46A, B ). The colour varies from purple to orange or yellow-green, unrelated to one sex or the other. The mature larvae are isolated in the upper part of the colony.

Amphipods inhabit the cloacal channels.

The size of the zooids varies slightly with colony size, and in the same double row their size increases from the base of the row to the common cloacal opening. The oral siphon is very short with six teeth. The branchial sac is not contracted ( Fig. 46A ). In the largest female zooids, we count- ed about 20 stigmata in the first half row and 19 in the fourth half row, 19 and 18 in male zooids. The cloacal opening is wide; the upper margin elongat- ed in a languet with a round tip. Both siphons have a weak muscular sphincter.

The abdomen and thorax are linked by a narrow waist ( Fig. 46A, B ). The stomach is barrel- shaped, not clearly separated from the tubular remainder of the gut. The anus has two lobes. A small number of sinuous but parallel pyloric tubules lines the rectum. They converge at an elongate ampulla in the gut loop which opens by a short channel into the middle of the stomach.

The gonads are in the gut loop. The immature ovary lies in the gut loop, but as it develops, it becomes pedunculate and projects from the abdomen ( Fig. 46B ).

The testis, with four to six lobes in a cluster lies inside the gut loop ( Fig. 46A ). The sperm duct makes a hook at the bottom of the abdomen and follows the rectum.

The embryos ( Fig. 46C ) are quickly separated from the mother zooid. The brood pouch hangs by a very short peduncle from the thorax, under the cloacal aperture. There is a single embryo in each pouch. The developed larvae ( Fig. 46C ) all lie in the upper part of the colony, in the tunic. Their trunk is 0.8 mm long; the tail describes a little more than one turn around it. The three long, conical adhesive papillae diverge from each other; four rows of stigmata and the gut are already differentiated, and one to three very small buds are to be found in the ventral part of the larva. There is an otolith but no ocellus ( Fig. 46C ).

The epicardic tube has not been seen.

REMARKS

These specimens correspond perfectly to those collected by the Astrolabe Expedition in 1829 at Western Port (southern Australia) which were briefly described by Quoy & Gaimard (1834). Three of those colonies are stored in alcohol in the MNHN collections ; one male and two females with larvae. One colony has two lobes and the peduncle is divided in two parts. One colony has the top part rolled. The colonies are well-preserved. There are 10 to 14 zooids in a row, more often 10 to 12. The zooids are slightly contracted and permit a detailed observation. We have not seen papillae at the colony surface but have found crystals, which may be of salt as they melt in water. We have counted up to 15 stigmata in the two last half rows. The ovary is pedunculate, protruding well outside the gut loop. The testis, with four lobes, also protrudes but remains in the basal part of the gut loop.

The larvae in these old specimens have the same size and anatomy as those collected in Komodo.

Sycozoa seiziwadai Tokioka, 1952 from the Arafura Sea is probably a synonym of S. cerebriformis . The colonies do not show differences in size or shape. Tokioka indicates 15 to 20 stigmata per row. This number is higher than that in the type but similar to what is found at Komodo. All other characters correspond. Tokioka’s description is short, and he only describes the colony shape. He probably did not know of Quoy & Gaimard’s work.

Figures

FIG. 46. — Sycozoa cerebriformis Quoy & Gaimard, 1834; A, male zooid; B, female zooid; C, larva. Scale bars: A, C, 0.5 mm; B, 1 mm.