Pelonaia bursaria Redikorzev, 1941

Sanamyan, Karen & Sanamyan, Nadya, 2012, Deep-water Ascidiacea from the Sea of Japan, Zootaxa 3245, pp. 63-68 : 66-67

Pelonaia bursaria Redikorzev, 1941

( Figure 2 )

Pelonaia corrugata forma bursaria Redikorzev, 1941: 188 . Pelonaia corrugata bursaria: Nishikawa, 1991: 129 .

Material examined. St. B 7-8, 532m, 1 specimen.

Description. The single specimen is about 2.5 cm long and 1 cm diameter. The posterior end is rounded and an anterior extremity of the body has an abrupt narrowing where branchial and atrial orifices are set close together. The test is thin and firm. Hair-like processes with few attached sand grains are present only around the posterior end of the body and form a wide ring around it ( Figure 2 A). Otherwise the test is smooth and not wrinkled (as in typical P. corrugata ) and almost free from foreign matter with only occasional minute grains of sediment attached. Thick crowded circular muscles are present only on siphons while on the whole rest part of the body wall only occasional thin transverse muscle fibers can be detected after staining. In contrast the longitudinal muscles are well developed and continue to the end of the body, although muscle fibers are much thicker on its anterior half.

About 18–20 branchial tentacles arise from the branchial velum. Prepharyngeal band runs close to the velum and draws a circular line with shallow dorsal V around large oval dorsal tubercle which has C-shaped opening. Dorsal lamina is a high plain-edged membrane. The branchial sac has one shallow but distinct fold on each side running on some distance from the dorsal lamina, otherwise its wall is quite smooth. Internal longitudinal vessels are very numerous and closely set, with no more than one stigmata between two adjacent vessels.

The gut forms a deeply curved loop along postero-ventral end of the body, the secondary loop widely open and long rectum curves anteriorly at a right angle to the descending part of the loop. The stomach occupies about half of the length of the ascending limb of the gut loop, it has 22 prominent internal longitudinal folds and a small straight caecum on distal end.

One gonad is on each side of the posterior half of the body wall. Long tubular ovary makes a widely open arc so that in most its way it runs more or less transversely in relation to the body axis. The ovary is surrounded by numerous crowded small oval testis follicles.

The endocarps are rather large and present only on posterior half of the body: one endocarp is within the arc forming by each ovary, and several are on the body wall below (posterior) to gonads, including one endocarp in the gut loop.

Remarks. The taxon was originally established by Redikorzev (1941) as a forma bursaria of Pelonaia corrugata Goodsir et Forbes, 1841 and then raised to a subspecies status by Nishikawa (1991). Original description is based on several specimens from the Sea of Okhotsk and Sea of Japan and no other specimens referable to this taxon were recorded until now. Redikorzev (1941) distinguished his 'forma' by several features which he thought are connected with the less elongated body in comparison with the typical P. corrugata , e.g. position of the gut loop and L-shaped instead of U-shaped gonads. However, as it become clear after examining of newly collected specimen, the differences appear to be more pronounced and Redikorzev's taxon probably deserves a rank of a separate species. The differences in the general shape of gonads in P. corrugata and P. bursaria are too prominent to be explained by different proportions of the body wall, and gonads differ not only in the shape but also in the form of male follicles, these are small, rounded or oval in P. bursaria and long sausage-shaped, mostly parallel to each other in P. corrugata . The stomach of P. bursaria is much shorter than in P. corrugata where it occupies almost entire ascending limb of the gut loop (see, for example Monniot, 2011, Fig.6). Pelonaia corrugata has perfectly flat wall of the branchial sac, while P. bursaria has low but quite distinct branchial fold on each side. We reexamined several available small and large (2–8 cm) specimens of P. corrugata from the Sea of Japan and the mentioned features (flat branchial sac, very long stomach, the shape of gonads and endocarps) appear to be stable and not depending on the size of the specimens.

Figures

FIGURE 2. Pelonaia bursaria. A, intact specimen; B, specimen with tunic removed, showing left gonad and gut loop; C, specimen opened ventrally.