Aplidium discum, Monniot, 2021

Monniot, Francoise, 2021, New records of deep-sea ascidians (Tunicata, Ascidiacea) from the New Caledonia region, Zootaxa 4996 (3), pp. 443-468 : 445-446

Aplidium discum sp. nov.

Figure 2

Station: Kanacono DW 4666 (Syntypes MNHN A1 .APL.B 577). Three specimens .

The three disc-shaped colonies are densely impregnated with sand ( Fig. 2A, B ). The largest, 35 mm in diameter, is 10 mm thick in the centre. The zooid arrangement is hardly visible, in double lines radiating from a central common narrow atrial aperture. The contracted zooids are short ( Fig. 2C ) with the thorax and abdomen each measuring 1.2 mm. The oral siphon has six lobes. An atrial languet triangular or with one to five apical teeth arise from the upper rim of a narrow atrial aperture. The branchial sac has ten rows of stigmata. The gut loop is short with a stomach with four longitudinal folds. A strong muscular ribbon extends along the entire length of the postabdomen on each side. The gonads are either male or female in the same colony the testis comprised of a few grouped vesicles; the ovary has only one oocyte. A tadpole incubated in the thorax fills the whole atrial cavity ( Fig. 2C ).

This species is distinguished by the plate-like shape of the colonies, the small zooids with gonads reduced to a small volume in a short postabdomen. The genus Aplidium is uncommon in deep habitats of the Caledonian region.

Figures

FIGURE 2. Aplidium discum sp. nov. A, B, both sides of a colony, scale bar = 1cm; C, two zooids.