Aplidium minithorax, Monniot, Françoise, 2012

Monniot, Françoise, 2012, Some ascidians from the southern coast of Madagascar collected during the “ AtimoVatae ” survey, Zootaxa 3197, pp. 1-42 : 11-12

Aplidium minithorax n. sp.

( Figures 8, 9A)

Stations. TR 7 ( MNHN: A 1 APL.B 545). TA 25 ( MNHN: A 1 APL.B 56). TA 29 ( MNHN: A 1 1 PL.B 544, type).

The holotype is about 20cm large, made of several coalescent and more or less flattened lobes ( Fig. 9 A). The tunic is entirely filled with sand, hard, and does not let see the zooid arrangement. The zooids remain orange in formalin, densely packed, perpendicular to the colony surface. They reach 1cm in length but are contracted ( Fig. 8 A). The oral aperture has 8 short lobes. A tridentate languet starts from the anterior rim of the atrial siphon ( Fig. 8 B). There are 5 to 6 longitudinal muscle fibres on each side of the thorax. The branchial sac ( Fig. 8 C) is short with 5 rows of stigmata and 10 to 12 stigmata in a half row, they are difficult to count according to the contraction. The stomach wall has 5 deep folds ( Fig. 8 B). The post-abdomen is longer than the thorax plus the abdomen ( Fig. 8 A). The ovary takes place at a short distance from the abdomen and is followed by one or two rows of few testis vesicles limited to the anterior half of the post-abdomen. A single larva is incubated in the thorax ( Fig. 8 D). The trunk measures 550 to 650 µm, circled by a tail in one turn. The 3 adhesive papillae are separated by odd ramified vesicles. A crescent of dense, very small vesicles lies on each side of the adhesive papillae.

A minithorax n. sp. has in common with A. mernooensis ( Brewin, 1956) the 8 oral lobes, the branchial sac and the stomach. It differs by the colony shape, made of circular lobes of a single system in the New Zealand species.

Another Aplidium species with 5 rows of stigmata: A. petrense ( Michaelsen, 1919) is recorded from Zanzibar, Mozambique ( Millar, 1956) and Madagascar ( Vasseur, 1970), but the colonies are devoid of sand and the stomach wall has numerous folds.