Dendrodoa aggregata ( Rathke, 1806 )

Sanamyan, Karen & Sanamyan, Nadya, 2017, Shallow-water Ascidians from Matua Island (central Kuril Islands, NW Pacific), Zootaxa 4232 (3), pp. 301-321 : 303-305

Dendrodoa aggregata ( Rathke, 1806)

( Figure 3 )

Ascidia aggregata Rathke, 1806: 11 .

Dendrodoa aggregata: Van Name, 1945: 275 (synonymy). Nishikawa, 1991: 127. Sanamyan, 2000: 72.

Material examined. Matua Island, Point Crocodile, 11m, four specimens (#165); Point Kluv , 16 m, one juvenile specimen (#165).

Description. Most specimens are strongly damaged and contracted ( Figure 3 A). The description of internal characters is based on one small undamaged specimen.

The specimens grow in a tight aggregate of several specimens. The test is heavily covered by sponges, bryozoans and sand particles. Limits between the specimens and siphons of individual ascidians cannot be recognized on the preserved material and as a whole the material looks like a lump of stones mixed with sand and epibionts, rather like a solitary ascidians.

The body removed from the tunic is sac-like, sometimes with a short peduncle, opaque and dark, with a strong brownish-violet tint and blotches of red in freshly preserved specimens ( Figure 3 B). The siphons are short and terminal, situated close to each other, four-lobed and bright red. About 25 branchial tentacles are present, a half of them are large and other are very small, alternating with the larger ones. Cloacal tentacles are short and filiform, about 30 in number. Large prominent dorsal tubercle has a C-shaped slit with the open interval directed obliquely to the left. The prepharyngeal band is composed of a single thick and high lamella running on some distance from the ring of tentacles and making wide shallow V around the dorsal tubercle. High dorsal lamina has a plain margin. Internal longitudinal vessels on anterior part of the branchial sac of dissected specimen are distributed as follow: EN1(5)1(7)1(5)0(8)0DL0(10)1(4)1(6)1(4)1. In the proximal part of the branchial sac (closer to the bottom) the most ventral folds on each side disappear and the total number of longitudinal vessels is fewer ( Figure 3 C). The gut forms narrow J-shaped loop, secondary loop widely open. The stomach is voluminous, about twice as long as wide, poorly demarcated from the intestine, with a small caecum. Its internal wall has longitudinal plications, but they are not well visible from the exterior. The rectum is short, opens just under the atrial siphon. Anal margin bi-lobed, smooth. One branched tubular gonad is on the right side of the body only. It is somewhat embedded to the body wall. In the examined specimen the gonad consists of three branches, posterior branch is divided in two ( Figure 3 D). Endocarps, of various sizes, are numerous and distributed over the whole inner body wall.

Most internal organs, including the tentacles, branchial sac, gut loop and gonad have a strong violet tint ( Figures 3 B–D show its natural colour, the specimen is not stained).

Remarks. The record is within the known range of Dendrodoa aggregata . The gonad with only three branches is atypical for this species and that is attributed to the small size of the examined specimen. A gonad with three branches is characteristic for D. pulchella (Verrill, 1871) . However, D. pulchella typically has smooth thin test, smaller stomach (although this character is variable) and more numerous tentacles. Both species are common in N Pacific, and, in particular, in waters around Kamchatka, but D. pulchella typically occurs somewhat deeper, it is not present in our material from East Kamchatka and Bering Sea collected by divers, but is abundant in trawl samples, while D. aggegata is common in diver accessible depths too.

Figures

FIGURE 3. Dendrodoa aggregata. A, intact specimens; B, specimen with test removed; C, specimen opened ventrally; D, same, with branchial sac removed.