Pyura styeliformis, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 345-348

Pyura styeliformis n. sp.

( Figs 107 ; 108B ; 130C )

TYPE MATERIAL. — Palau. Koror, Ngermerrangel Island, Flatworm Lake, marine lake, cave, 7°19.12’N, 134°30.40’E, 1 m, 23.VII.1997 ( MNHN S2 PYU 391).

ETYMOLOGY. — From the Latin forma: shape and the genus Styela .

DESCRIPTION

This cave-dwelling species, 1 to 1.5 cm in diameter, has a smooth tunic that is slightly wrinkled around the siphons. It seems gregarious, as the individuals attach to each other, with young settling on adults ( Fig. 130C ). In some cases the tunics can fuse. The animal is globular. The oral siphon is terminal, the cloacal siphon is clearly mid-dorsal. Both siphons have long, sharp and dense spinules of equal size: about 100 µm ( Fig.108B ). The pink-ochre colour persists in fixatives. The appearance is unusual for a pyurid: it more resembles a styelid ( Fig. 130C ) (hence the species name).

The musculature is weak. It comprises about 30 thin ribbons arising from each siphon. Near the gonads the ribbons disintegrate to make anastomosed fibres. The body wall is transparent. The siphons are red as is the external tunic. The tentacles are not numerous, about 10 of two or three orders, located anteriorly in the oral siphon. They are poorly ramified and the smallest are simple ( Fig. 107H ). The prepharyngeal band has two equal rims. It is wavy around the tops of the branchial folds and makes a slightly dorsal indentation. The dorsal tubercle has a small, simple opening. The rather short dorsal lamina is made of short languets. The branchial tissue is thin with six high folds on each side. The right side formula is: R.E. 5 9 6 15 6 19 6 20 5 18 3 17 3 D.L.

At the oesophageal entrance the folds lower rapidly. The longitudinal vessels do not protrude as blades or papillae. Between the folds, the stigmata are irregular; we counted three to five of them in a mesh. But they are very regular on the folds, with three to four in a mesh. They are short and wide open. There are no parastigmatic vessels. At the top of the folds the stigmata are short, sometimes curved.

The limbs of the digestive tract lie well apart ( Fig. 107A, C ). The oesophagus is short, and the undilated stomach is covered by a colourless, unramified hepatic gland made of two anterior lobes and a large posterior lobe ( Fig. 107C ). The cylindrical intestine ends in a short rectum. The anus is more wavy-edged than lobed. The gonads are attached to the body wall by their whole surface. Each is made of an irregularly lobed ovary and testes covering the extremities of the ovarian lobes ( Fig. 107B, C ). The ovaries are long; their papillae open close to each other and close to the anus. The sperm ducts of each lobe gather at the ovary surface into a common duct which opens against the oviduct in a small, scarcely visible papilla ( Fig. 107I ).

The development of the gonads is not synchronous on the two sides of the body. In small specimens ( Fig. 107D, E ) the right gonad develops early and the male part becomes functional, while the left gonad is not visible. Later, the left gonad appears but remains late compared to the right gonad ( Fig. 107F, G ). When the right side male and female parts are both functional, on the left only the testis is well-developed. In large individuals, however, both gonads are equivalent.

There are only a few endocarps on some male lobes of the right gonad and the external side of the gut loop ( Fig. 107C ).

Figures

FIG. 107. — Pyura styeliformis n. sp.; A, B, left and right sides of the body; C, body ventrally opened; D-G, both sides of two different bodies; H, oral tentacles; I, gonoducts. Scale bars: A-C, 5 mm; D-G, 1 mm; H, I, 0.5 mm.

FIG. 108. — Siphonal spinules; A, Pyura gangelion (Savigny, 1816); B, Pyura styeliformis n. sp.; C, Microcosmus bitunicatus n. sp.; D, Microcosmus pacificus n. sp. Scale bars: 100 µm.

FIG. 130. — A, Herdmania polyducta (Monniot C. & Monniot F., 1989); B, Pyura gangelion (Savigny, 1816); C, Pyura styeliformis n. sp.; D, Microcosmus bitunicatus n. sp.