Aplidium redikorzevi

Aplidium redikorzevi nom. nov.

(Figures 6,7)

Amaroucium fragile Redikorzev, 1927: 384.

Material examined. Commander Islands, Medny Island, about 10 colonies and fragments from 5 to 20m collected in Summer 1992 and 1995.

Description. Colonies are composed of numerous crowded upright sandy lobes, each is 5–6 mm in diameter and up to 35 mm long but often much shorter. The lobes arise from a basal mass attached to substratum (Figure 7).

The sand is present internally and densely covers the surface making the colonies very cryptic and difficult to recognize underwater. Zooids are parallel to each other and vertical, they open on the flattened top of the lobes. Each lobe probably contains a single system of a few zooids arranged in a circle.

The zooids in all colonies are strongly contracted and small, typically about 3mm long, occasionally up to 7mm. Numerous thick longitudinal muscles arising on the thorax join together to form a strong ventrolateral band on each side of the ventral line of abdomen and run to the end of postabdomen. Atrial languet is simple but has three short indentations at the end. The branchial sac has 12 rows of about 15 stigmata. The stomach has five very prominent folds. Ovary, when present, is just below the gut loop, testis follicles fill the whole length of postabdomen.

Remarks. Amaroucium fragile Redikorzev, 1927 is a junior secondary homonym of Psammaplidium fragile Herdman, 1899, so new name is here proposed for this species. The species was known only from the original description based on specimens from Shantar Islands, Sea of Okhotsk. The species still has not been recorded in Kamchatka.