Molgula dione

Molgula dione (Savigny, 1816)

(Figure 35)

Molgula dione Savigny, 1816: 93 153 Pl.7 fig. 1. Monniot C. 2002: 115 fig 38 and synonymy, Yemen, Socotra Station. TA 56 (MNN S3 MOL.A 394)

The single specimen 5mm in diameter is spherical, covered with sand; the siphons are not visible at the surface. Removed from the tunic the edge of the siphons is cut into numerous thread-like lobes. The body wall is thin. The longitudinal muscular fibres issued from each siphon do not extend on the whole body length (Fig. 35 A). The transverse muscles are very thin. A velum is present in both siphons. The oral tentacles are large but poorly branched. The dorsal tubercle opens in a vertical slit; it is located in a deep V of the peripharyngeal band. The dorsal lamina is short. The branchial sac (Fig. 35 B) has 7 folds with the formula: right-E 3-6-5-6-6-5-2-DL-3-4-5-5-5- 4-3E left. The first dorsal fold on each side is very short. The double spirals are obvious at the top of the folds. Parastigmatic vessels are present. The gut is a long closed loop. The hepatic gland in a single lobe has round papillae. There is one gonad on each side (Fig. 35 A); the testis is against the proximal end of the ovary. The ovary is globular with a short oviduct. The sperm duct ends in a short tube protruding on the internal side of the ovary. The renal sac is oval and small.

All characters well correspond to previously collected specimens, the smallest number of branchial folds is attributed to a smaller size of the Madagascar specimens.

The species was previously recorded from the Red Sea and Yemen.