Aplidium eborinum, Sanamyan, Karen & Sanamyan, Nadya, 2011

Sanamyan, Karen & Sanamyan, Nadya, 2011, Shallow-water species of the genus Aplidium (Ascidiacea) from Kamchatka and Commander Islands, Zootaxa 2922, pp. 41-50 : 46-47

Aplidium eborinum n. sp.

(Figures 4,5)

Aplidium glabrum: Sanamyan, 1998: 119 ; 2000: 213 (part, specimens from Kamchatka); Sanamyan, Sanamyan, 2010: 242.

Material examined. Kamchatka, Avacha Bay: Bezimanny Point, 6–8m, 7.08.2004 (Holotype KBPIG 1442/1); Kekkurny Point, 19m, 26.07.2006 (Paratype KBPIG 1443/2, 2006-07-26-02); Piramidny Point, 18m, 14.02.2007, several large colonies; Starichkov Island, 10–11m, 18.10.2008, one colony (Paratype KBPIG 1444/3).

Description. The colonies are thick encrusting masses with the surface raised into large domes or rounded stumpy lobes with large common cloacal apertures on the top. Sometimes the lobes are more separated and connected to each other only by thick anastomoses of the basal test ( Figure 5 A). The largest collected colony is about 10 cm in extent and up to 5 cm thick. The colour is rather constant and varies in a limited degree from light yellowgrayish to white, sometimes with a light bluish opalescence on the underwater photographs. In preservative (formaline) all colonies are light grayish or brownish. The test is gelatinous and rather opaque, zooids are not visible well through it. The surface is always clear from foreign particles but sparse sand grains may present internally. Zooids are arranged along rather thick branching cloacal canals converging to sessile common cloacal apertures. In preservative the surface of the lobes is smooth, without depressions or ridges indicating systems.

Zooids are rather short and in most preserved specimens strongly contracted, being no more than 7 mm long. They are almost parallel to each other and open at angle to the surface of the colony lobes. Branchial siphon has six lobes. Small atrial aperture has always simple and usually short atrial languet. Numerous closely set thin longitudinal muscles are on each side of the thorax. The branchial sac has 14 rows of stigmata. Cylindrical stomach has 13– 15 wide and usually very regular and prominent folds. Post pyloric part of the gut loop has usual duodenum, midintestine, posterior stomach and short wide rectal valves. Ovary consisting of one or two large ova is in the middle of postabdomen and testis follicles are confined to the posterior half or third of postabdomen.

Up to six larvae incubated in the atrial cavity of some zooids in holotype. The trunk is 0.9mm long. There are three adhesive organs on long thin stalks and an arch of rather large and closely set epidermal vesicles arranged in a single row around each side of the anterior half of the larval trunk, but no median or lateral ampullae.

Remarks. Colonies of this species from Avacha Bay were identified previously as A. glabrum (Verrill, 1971) described originally from Atlantic coast of North America. Indeed, they have similar zooids with almost the same number of rows of stigmata and stomach folds, although atrial languet in A. glabrum usually has additional lateral lobes completely absent in the specimens from Kamchatka. Colonies of A. glabrum are described as consisting of club-shaped flat-topped heads with abrupt sides which in larger colonies may have wide bases. We had a chance to examine colonies referable to A. glabrum from Norway, they consist of low flat-topped lobes with parallel vertical zooids open perpendicularly to the upper surface. These colonies correspond exactly to a schematic but quite precise figure provided by Millar (1966, Figure 14a) and differ substantially from the colonies of the present species. It seems that A. glabrum is restricted to North Atlantic and European seas and probably not occurs in Pacific.

Specimens from South Kurile Islands identified by Sanamyan (2000) as A. glabrum appear to be distinct from the present species, the structure of systems is not recognizable, the larva is very similar but smaller, and zooids have only 9 or rarely 10 rows of stigmata. However, the specimens from Kamchatka described in the same paper belong to A. eborinum n. sp., although Sanamyan (2000, Figure 2 D) misinterpreted the shape of systems in preserved colony and figured them as irregularly oval or circular.

Figures

FIGURE 2. Aplidium dissectum n. sp. A, zooids; B larva (2006 - 10 - 15 - 04); C, colony (2004 - 07 - 28 - 03).

FIGURE 5. Aplidium eborinum n. sp., underwater. A, specimen 2004 - 06 - 03 - 01; B, specimen 2006 - 07 - 26 - 02.