(Figures 25A, 26)

Cynthia arenosa Herdman, 1882: 140.

Pyura arenosa: Kott: 1985: 289 Figs 138a,b, 139, without synonymy.

Material. Coll. N.J. Pilcher et al., Viet Nam, Con Dao Isl., Con Son Isl., 08°41.12’N – 106°36.80’E, 1m, 29/ VII/2008, 0PHG 1713-U (MNHN S2 PYU 484).

The specimens are oval and entirely covered with coarse sand. The apertures, one apical and the other at 1/3 of the body length are white with brown stripes in life and show iridescent spinules. The siphonal spinules are long thin spines 120µm in length (Fig. 25A). A dorsal groove connect the siphons. The tunic is thin and translucent after removing the sand. The body wall is very thin with red pigment at the siphons. Muscular ribbons radiate from each siphon but do not extend over the whole body; thin fibres, essentially transverse, occupy the ventral side.

There is an oral velum. Sixteen oral tentacles with two orders of ramifications, and smaller ones intercalated, are implanted on the rim of a thick blade. The dorsal tubercle opens on the right in a C. The branchial tissue is thin with 6 folds on each side (Fig. 26A) and 5 longitudinal vessels between each of them. The vessels end in long papillae at the oesophagus entrance. The dorsal lamina is short with sharp languets. The long gut loop occupies a large part of the left body side (Fig. 26B). The long oesophagus is narrow followed by a stomach not well delimited. The hepatic gland is divided into 3 unequal lobes: two of them on each side of the cardia have small spiny papillae, another in cauliflower covers the internal side of the stomach. No endocarps were found on the intestine. The secondary loop of the intestine is wide but short ending in a 4 lobed anus. There is one curved gonad on each side of alternating hermaphrodite lobes along a central ovary (up to 14) (Fig. 26B). Each gonad lobe has an endocarp. The gonoducts open close to the atrial siphon. No endocarps were found on the body wall.

The specimens from Viet Nam correspond well to specimens described by Kott(1985) loaned by the Western Australian Museum and others loaned by the Queensland Museum.

Pyura arenosa is a shallow water species already recorded from Indonesia and Australia.