Polycitorella Michaelsen, 1924

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 250-253

Genus Polycitorella Michaelsen, 1924

Polycitorella coronaria Monniot F., 1988 ( Figs 39 ; 118D )

Polycitorella coronaria Monniot F., 1988: 228 . Type locality: South Australia. Synonymy: see Kott 1990: 184, fig. 68, South and western Australia.

MATERIAL EXAMINED. — Papua New Guinea. Louisiade Archipelago, Calvados Island Chain, Brooker Channel, 11°03.09’S, 152°28.62’E, 12 m, 1. VI.1998 (Sample: CRRF). — Louisiade Archipelago, N side Tagula Island, Ima Channel, 11°25.92’S, 153°26.78’E, 7 m, 4. VI.1998 ( MNHN A3 POL.B 5). — Coral Sea, Eastern Fields, 10°02.22’S, 145°33.01’E, 25 m, 14. VI.1998 (Sample: CRRF). — Coral Sea, Eastern Fields, 10°00.66’S, 145°39.90’E, 12 m, 14. VI.1998 ( MNHN A3 POL.B 6).

DESCRIPTION

The colonies are flat cushions, the largest 4.5 × 2.5 cm across and 12 mm thick. The tunic’s consistency is firm. The colour in life is white ( Fig. 118D ) or grey, while in formalin the animal is pale grey with black inclusions at the level of the oesophagus. The pigment cells are mostly distributed in the upper layers of the colony; at the surface and around the thoraces. The thoraces can be extracted easily, but the abdomens are more tightly encased in the tunic. Spicules in the tunic are sparse, and they are less numerous in the upper layer, but denser in the abdominal layer. They are stellate, comprising bi-pyramidal rays, and small, 45 µm in diameter. They are often dissociated or grouped into irregular balls. The zooids are arranged in stellate systems of six to seven individuals, the oral siphons far apart in a circle and the cloacal siphons grouped in the centre.

The zooids ( Fig. 39A, B ) are 1 to 1.5 cm long, the thorax equal to the abdomen except when retracted. The oral siphon has six lobes with flat tips. The cloacal siphon is very long, ending in six equal lobes. The thoracic musculature has transverse and longitudinal fibres regularly crisscrossed on the thorax, united in two bundles on the abdomen.

There are 24 oral tentacles in three orders of size. The branchial sac is elongated with up to 18 rows of stigmata, and there are 30 to 40 stigmata in the first row. There are no parastigmatic vessels. The digestive loop is straight; the ovoid stomach is asymmetrical with its dorsal side shorter. There is a short, annular post-stomach ( Fig. 39B ) separated by a constriction from a short, round midintestine ( Fig. 39C ). The rectum begins without caeca in the descending limb of the gut loop. It makes a slight curve facing the mid-intestine. The bilobed anus opens at the base of the branchial sac ( Fig. 39A ). The gonads lie in the gut loop. The colonies were either male or female ( Fig. 39D, E ). No larvae were mature: only embryos were found in the oviduct, against the oesophagus.

REMARKS

This species has a very variable colour pattern in life, from pure white to grey, but always has a grey tint in formalin. The number of stigmata rows is variable and increases with the size of the zooid and of the colony.

This widely distributed species has been collected in southern and western Australia ( Kott 1990; Monniot F. 1988) and now in Papua New Guinea.

Polycitorella mariae Michaelsen, 1924 ( Figs 40 ; 41A ; 118E )

Polycitorella mariae Michaelsen, 1924: 279 , figs 5; 6. Type locality: New Zealand. — Monniot F. 1988: 227, fig. 13, pl. IIIE, F, Chesterfield Islands .

MATERIAL EXAMINED. — Fiji. Viti Levu, Beqa Passage, Shark Reef, 18°18.08’S, 178°01.05’E, 26.X.1996 ( MNHN A3 POL.B 4). — Viti Levu, Suva Harbour, 5-15 m, coll. Ireland ( MNHN A3 POL.B 18).

DESCRIPTION

The colonies make very hard cushions 2 cm in thickness and up to 4 cm in diameter. The oral siphons are stellate, grouped in irregular circles around a depression of the tunic in which the cloacal siphons open. The general surface is smooth. The colony’s colour in life is cream or pale yellow ( Fig. 118E ); its zooids are yellow. In formalin preservative the colonies are white. The zooids lie parallel to each other and perpendicular to the colony surface.

The zooids ( Fig. 40A ) are generally very contracted. Both siphons are tubular with six lobes, the cloacal siphon often longer. The body wall is thick and opaque with a strong longitudinal musculature extending below the thorax in two ribbons along the abdomen. There are 14 rows of stigmata. A narrowing separates the thorax and abdomen. No crease of the body wall was seen there.

The gut loop is straight ( Fig. 40A, B ). The stomach, asymmetrical with a smooth wall, lies low in the abdomen. The post-stomach and the midintestine are cylindrical.

The gonads lie in the gut loop below the stomach. There are numerous round testis lobes ( Fig. 40B ). The ovary is central. There is one larva incubated at a time in the inflat- ed cloacal cavity. The trunk is 1.2 mm long. It has three adhesive papillae in a line and four pairs of elongated ampullae ( Fig. 40C ), and sometimes an additional lateral ampulla. The tail is curled in half a turn around the trunk.

The small spicules have diverse sizes, the largest about 35 µm, but always with the same shape, irregular balls made of short fibrous rays ( Fig. 41A ).

REMARKS

The diverse colonies collected in the Fiji Islands have different shapes – cushions or lobes with short peduncles – but the base of the colony from which these elements arise is always thick. The size of the zooids and the number of stigmata rows increase with the size of the colony. The spicules in our specimens are the same as in the type specimen. Kott (1990) created P. orientalis for a species from Queensland that she synonymized with Polycitorella mariae identified by F. Monniot (1988) in the Chesterfield Islands. Her species, without larvae, does not show characters justifying a synonymy. The arrangement of spicules in sheets around the abdomens and their absence elsewhere between the zooids seem distinctive of P. mariae .

Figures

FIG. 39. — Polycitorella coronaria Monniot F., 1988; A, B, two parts of a zooid; C, shape of the gut; D, abdomen with a female gonad; E, testis. Scale bars: A-C, 1 mm; D, E, 2 mm.

FIG. 118. — A, Eudistoma sp.; B, Polycitor giganteus (Herdman, 1899); C, Polycitor translucidus Kott, 1957; D, Polycitorella coronaria Monniot F., 1988; E, Polycitorella mariae Michaelsen, 1924; F, Polycitorella stellifera n. sp.

FIG. 40. — Polycitorella mariae Michaelsen, 1924; A, zooid; B, testis; C, larva. Scale bars: A, B, 1 mm; C, 0.5 mm.

FIG. 41. — Spicules; A, Polycitorella mariae Michaelsen, 1924; B, Polycitorella stellifera n. sp. Scale bars: 10 µm.