Distaplia alaidi Sanamyan, 1993

Sanamyan, Karen & Sanamyan, Nadya, 2017, Shallow-water Ascidians from Matua Island (central Kuril Islands, NW Pacific), Zootaxa 4232 (3), pp. 301-321 : 316-318

Distaplia alaidi Sanamyan, 1993

( Figure 12 )

Distaplia alaidi Sanamyan, 1993: 170 .

Material examined. Matua Island, Point Kluv, 15 m, several specimens in two lots (#77, 157).

Description. Colony consist of one, two, or rarely three spherical or oval heads, up to 1.5 cm diameter, but usually less than 1 cm, supported on a thin, no more than 4 mm diameter, long (up to 4 cm) stalk. The stalk is sharply demarcated from the head. Its basal part creeps along the branches of hydroids and bryozoans to which it is attached. In formaline the colonies are opaque white, soft, with zooids indistinctly visible from the exterior. The surface is clear, some sand grains occasionally present on the stalks. Underwater photographs ( Figures 12 B–D) reveal the peculiar structure of the colonies, totally obscured on preserved specimens. Each head contains a single system of zooids. A single large cloacal opening is on the top of each head. Its diameter is rather large and attains one third of the diameter of the head (in live state). The margin of the cloacal cavity is surrounded by the prominent round lobes, about 10 of them may be counted on some photographs. The cloacal cavity is very spacious, thoraces of almost all zooids in the head, with all four rows of stigmata completely exposed into the common cloacal cavity, can be easily seen through the cloacal opening. The zooids in the head stand almost vertically, with their dorsal sides facing to the axis of the colony. Branchial openings of individual zooids open on the surface of the upper half of the head, each opening is on the top of unusually long and wide thin-walled plain-edged siphon rising above the surface of the head and bent down (ventrally) ( Figure 12 D).

Zooids, with significantly contracted thoraces (in formaline) are about 6 mm long. The stigmata are very long, about 26 counted in the middle rows on each side of the branchial sac. Each row is crossed by a thick parastigmatic vessel. Four rows of stigmata are not grouped by two (as in Sycozoa ). The stomach is large, voluminous, asymmetrical, with its ventral side being longer than the dorsal, clearly demarcated from the intestine, contrasting deep-red in live specimens (visible on a smaller colony on Figure 12 B). Stomach wall presents small rounded swellings (or areolations) sometimes fused together and arranged in irregular longitudinal lines ( Figure 12 E). Gonads, consisting of rather numerous male follicles and several large ova are in the sack protruding from the posterior end of the abdomen. The examined colony contained numerous long brood-pouches located at the base of the colony head, below the zooids. The brood pouches are connected with the zooids by very long narrow connective, which is longer than the length of the zooid and easily tear when the zooids are extracted. They contain from one to five developing eggs in a single row, but no larvae were found.

Remarks. The species was known previously only from original description based on two specimens from Atlasova Island (which belongs to north Kuril group of islands). Sanamyan (1993), having only preserved specimens, failed to recognize the structure of the systems and a peculiar shape of the colony with long ventrally bent branchial siphons protruding from the colony surface. Current record from central Kuril Islands , where it is probably not rare, extends its known geographic range to the south. The species most probably is an endemic for Kuril Islands—during many years of investigation we saw no similar colonies in Kamchatka waters, and nothing similar is known from more southern locations. The species cannot be confused with any other Distaplia species or other colonial ascidian known from the region.

Figures

FIGURE 12. Distaplia alaidi. A, preserved colonies; B, colony underwater; C and D, the same colony, enlarged to show details of cloacal opening and orientation of branchial siphons; E, zooids.