Aplidium scabellum ( Michaelsen, 1924 )

Monniot, Françoise, 2012, Some ascidians from the southern coast of Madagascar collected during the “ AtimoVatae ” survey, Zootaxa 3197, pp. 1-42 : 12-13

Aplidium scabellum ( Michaelsen, 1924)

( Figure 9 B)

Amaroucium scabellum Michaelsen, 1924: 374 fig. 18.

Aplidium scabellum: Millar 1982: 26 figs 12–13 and synonymy, New Zealand.

Station. TR 7, (MNHN: A1 APL.B 543) The single colony 7cm in width and 2.5cm thick is made of joined lobes incrusted with sand ( Fig. 9 B). The upper surface of each lobe is alveolated. The oral apertures of the zooids open in a crest at the periphery of the hollows. The common cloacal aperture of each system opens through a naked short chimney, in the centre of the cavity. The internal part of the colony is filled with sediment. The zooids are long and thin, the thorax and the abdomen each measure 3mm, the post abdomen reaches 15mm. The oral siphon is long with 6 lobes; it remains yellow in formalin. The atrial opening is circular in a short tube at the level of the 3rd or 4th stigmata row. An atrial languet with a bilobed tip is inserted clearly above the siphon. The oral tentacles are short and numerous. A large space separates them from the peritubercular ring. The branchial sac has 19 to 21 rows of stigmata and 12 to 14 stigmata in a half row. The stomach wall has 5 longitudinal folds. An annular post-stomach is present. Two lateral diverticula mark the beginning of the rectum in the bottom of the loop. The anus with 2 lobes opens at the last but one row of stigmata. In the long post-abdomen the ovary is found far from the gut followed by a line of testis lobes down to the heart. The larvae are colourless included in the atrial cavity without dilatation. The trunk is 1.1mm long, the tail is wound in half a turn. The 3 adhesive papillae are short and spaced included in a large anterior crescent of very numerous ampullae. The sensory vesicle is located near the tail.

The lobes of the colony with straight sides and the crest around the zooid systems are characteristic. The colony surface with hollows and a dense incrustation with sand recall A. lunacratum . Both species essentially differ in the number of stigmata rows and the size of the larva. More than 20 rows of stigmata, 5 stomach folds and a languet inserted above the atrial siphon are not common characters taken together. All characters of the zooids and the larval structure are consistent with Millar’s (1982) description and figures.

A. scabellum was only known from New Zealand.

Figures

FIGURE 9. A, Aplidium minithorax n. sp. B, Aplidium scabellum.