Polyclinum arenosum Sluiter 1898

Polyclinum arenosum Sluiter, 1898

(Figures 12A, 13)

Polyclinum arenosum Sluiter, 1898: 20 pl. 4 Fig. 1–2, South Africa, Isipingo; Millar: 1955: 174; 1962: 135, South Africa, Natal.

Station. TA 12 (MNHN A1 POL.B 103).

The colony is entirely embedded with sand, in lobes erect on a common base (Fig. 12A). Each lobe contains 8 to 10 zooids. The thoraces are included in the inflated upper part of the lobes 5mm in diameter. The oral siphon has 6 pointed lobes. The rim of the atrial aperture extends in a long languet with a pointed or dented tip (Fig. 13 A). A round button is present behind the atrial siphon. The thoracic musculature is weak with 8 to 10 longitudinal fibres on each side, which do not extend farther than the level of the fourth stigmata row. The branchial sac (Fig. 13 B) has 14–15 rows of stigmata and 15 stigmata in a half row on the right side in the middle of the branchial sac. Fourteen round and short papillae are on a transverse vessel at the same level. The short abdomen and the post-abdomen in shape of a drop have the common shape of the genus (Fig. 13 A). One to 3 larvae are incubated in a pouch hanging at the middle of the thoracic wall. They have 3 adhesive papillae separated by odd vesicles and 4 pairs of lateral round vesicles (Fig. 13 C). The trunk 0.4mm long is circled by the tail in half a turn and contains an oxalate crystal. The colony from the south of Madagascar exactly fits with the descriptions by Sluiter and Millar for specimens from South Africa. The colony shape is unique among the genus.