Polycitorella graphicum

Polycitorella graphicum n. sp.

(Figures 23 A,C; 24)

Station. TA 51 (MNHN A3 POL.B 14, holotype).

The single colony is a thick crust 6cm in length and 1cm thick (Fig. 23 A). It is made of convoluted lobes protruding from a common base. The walls of the lobes are straight and the surface is flat. The zooids are lined along the outline of the lobes. The oral and atrial openings are projecting with a stellate design above the flat colony surface. The spicules (Fig. 23 C) are dense in the whole colony thickness except a thin layer on the side walls of the lobes. The zooids (Fig. 24 B) are deeply withdrawn into the colony. The largest individuals are 8 to 9mm long. The thoracic musculature is strong extending in 2 ribbons on the abdomen. The branchial sac has 13 rows of stigmata (Fig. 24 A). The stomach has a smooth wall. The intestine shows a bulbous segment before the rectum (Fig. 24 B). The gonads occupy the gut loop. The testis vesicles are poorly developed around a central ovary in this incubatory colony. The larva (Fig. 24 C) 1.9 to 2mm long takes place from the upper part of the abdomen to the basal part of the atrial cavity. It has 3 adhesive papillae and 6 pairs of lateral vesicles. Ocellus and otolith are in a posterior position. The tail encircles the trunk in half a turn. The larval trunk is dense no organs are already differentiated.

The spicules (Fig. 23 C) are stellate but irregular, from 20 to 30µm of diameter few of them reach 50µm.

P. graphicum n. sp. essentially differs from other species of the genus having more than 10 stigmata rows by the linear disposition of the zooids at the periphery of the colony, and by the design of the dark pigment cells. It lacks the thick aspicular tunic layer at the colony surface.