Aplidium vulcanium, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 218

Aplidium vulcanium n. sp.

( Figs 13 ; 113E)

TYPE MATERIAL. — Papua New Guinea. Milne Bay Province, East Cape, Boia Boia Waga Island, 30 m, 27. V.1999 ( MNHN A1 APL.B 419).

ETYMOLOGY. — From the Latin vulcanius: vulcanian.

DESCRIPTION

Two specimens were collected with colonies of the same ovoid shape, one 45 mm in height × 25 mm in diameter and the other 20 mm in height. The top side is depressed into a cup in the centre of which a long, funnel-like common cloacal siphon protrudes (Fig. 113E). The external wall of each colony is incrusted with sand and various epibionts up to the thick rolled rim of the hollow. The hollow and bottom of the cup and the tubular cloacal siphon are naked. The oral apertures do not protrude; they open in small groups in the deepest part of the hollow. The internal tunic contains sand but less densely than at the surface.

The tunic is dark blue-green in life and turns dark brown in formalin. It has a spongy consistency except on the top side (in the cup) of the colony, where it is smooth and thin.

The zooids ( Fig. 13A, B ) are about 18 mm long, parallel to the colony axis. The oral siphon has six finger-like lobes. The oral sphincter and the oral tentacle ring lie immediately behind the oral lobes. As the siphon widens toward the pharynx a large anterior inflated area precedes the prepharyngeal band ( Fig. 13C ).

The cloacal aperture, atop a short tube, opens in front of the third or fourth stigmata row ( Fig. 13C ). A thin, long languet is inserted well ahead of the siphon ( Fig. 13A, C ).

The body wall is thin. We counted a dozen thin longitudinal muscular fibres on each side of the thorax. The branchial sac contains 18 to 20 rows of stigmata. Stigmata are missing along the medio-dorsal line and under the line of rapheal languets, which is displaced on the left side ( Fig. 13G ). In the middle of the thorax we count- ed 13 to 14 stigmata in a row on the right side, a medio-dorsal space, then more seven stigmata, a dorsal languet, and then 11 stigmata on the left side. There is also a large unperforated band on each side of the endostyle.

The abdomen is shorter than the thorax. The stomach is cylindrical with seven or eight deep longitudinal folds ( Fig. 13D ). The annular enlargement of the post-stomach is moderate. The mid-intestine is short and globular. The rectum begins with caeca.

The post-abdomen is extremely long ( Fig. 13B ). The ovary is very far from the abdomen, and poorly developed when the testis begin to regress. The oocytes are very large ( Fig. 13E, F ).

A double row of numerous testis follicles extends through the posterior part of the post-abdomen down to the heart. No mature larvae were found in this material.

REMARKS

The long tubular common cloacal siphon protruding from a deep cup-like hollow is unique. It recalls the pattern found in each system in colonies of A. clivosum Kott, 1992 , Aplidium lunacratum Kott, 1992 and A. crateriferum ( Sluiter, 1909) . But in those species, the colonies comprise numerous systems and the common cloacal apertures are on shorter chimneys. In those species, the structure of the zooids is very similar, with long oral siphons, a cloacal languet anterior to the cloacal aperture, numerous rows of stigmata with an unperforat- ed area on each side of the endostyle, and very posterior gonads. In A. vulcanium n. sp., the stomach has more folds, seven or eight instead of the five in these three other species.

Figures

FIG. 13. — Aplidium vulcanium n. sp.; A, B, two parts of the same zooid; C, thorax; D, abdomen; E, F, ovaries; G, part of the branchial sac. Scale bars: A-C, E-G, 1 mm; D, 0.5 mm.