Pelonaia corrugata Goodsir & Forbes 1841

Pelonaia corrugata Goodsir & Forbes, 1841

(Figures 4 B, 5, 6)

Pelonaia corrugata Goodsir & Forbes, 1841. Forbes & Goodsir, 1841, pl.1 figs 1–3. Hartmeyer, 1903 and synonymy. Van Name, 1945 and synonymy.

Material. Canada, Grande Riviere, collection Ledoyer, (MNHN S1 PEL 1).

Few precise descriptions have been given of P. corrugata in spite of numerous specimens collected around the arctic and sub-antarctic seas. Several species names were given to this very common ascidian but the differences concerning the external aspect are considered non-significant (Hartmeyer 1903; Van Name 1945), varying with the contraction state or the substrate where they live. The most complete description until now is that of Van Name (1945), despite frequent further citations of collections made in various regions (Millar 1970; Nishikawa 1991 and synonymy; Sanamyan and synonymy 2010). Specimens of P. corrugata in the MNHN collections have been examined. Their anatomical description is based on the largest specimen 37mm long. The body is urn-shaped with both siphons joined at the narrow apical end (Fig. 5 A). The tunic has numerous transversal ridges impregnated with fine sediment and wears some short tunic filaments at the enlarge base (Fig.5 A). All specimens have the same aspect and seem to have been free-living on the sediment. The body wall contains strong muscular ribbons on the halfanterior part, and thinner ones posteriorly. The oral tentacles are short and filiform. The protruding dorsal tubercle opens in a simple hole. The branchial sac is flat, very contracted and linked to the body wall by numerous bridles; it does not reach the bottom of the body cavity. The dorsal lamina is long, undulated by contraction, with a smooth rim. I have counted 28 longitudinal vessels on the right side and 36 on the left side, not grouped in folds (Fig. 5 B). They are more numerous than the number indicated in the literature. The round or oval stigmata are often cut by parastigmatic vessels (Fig. 5 B). The gut loop is long but remains in a small part of the posterior left body side (Figs 4 B, 6AB).. The narrow and long oesophagus enters in a long plicated stomach which has a caecum at its pyloric part (Fig. 4 B). A caecum was also noted by Årnback-Christie-Linde (1952). The intestine is applied against the whole length of the stomach and then curves at the oesophagus level to follow the dorsal body line. The anus is lobed. The gut is only linked to the body wall by strands of tissue. The gonads (Figs 4 B, 6AB), one on each side, have a peculiar shape. They occupy the most part of the body wall surface. The ovary is U-shaped, each limb bordered on both sides by finger-like lobules pressed to each other and making a flat ribbon against the body wall (Fig.4A, 6 AB). The left gonad lies above the gut loop. The male and female papillae are joined and apical. Small endocarps are irregularly scattered on the posterior part of the body wall, inside the gut loop and few of them are intercalated between the male lobules of the gonads (Figs 4 B, 6). A triangular line of ramified tentacles is at the base of the atrial aperture and some filiform papillae arise from the internal lining of the siphon.

The main differences between both species of Pelonaia concern the tunic structure, the number of branchial longitudinal vessels, the shape of the male vesicles.