Polymastia kurilensis Koltun 1962

Polymastia kurilensis Koltun, 1962

Fig. 6 A, 7A–D

Polymastia laganoides of Burton, 1935, non Lambe 1895.

Material examined. KML 1020, PBS sta. 63-74, off Kodiak I., Alaska, (58° 07.8′N, 150° 52.0′W), 126 m depth, no date, coll. unknown, one specimen.

Description. Macroscopic features. Specimen not observed in life. Sponge cushion-shaped, 5 cm diameter fragment, 2 cm thick. Papillae small and conical with rounded apices, 1 mm high x 1.5 mm wide at base; multiple papillae on fragment (Fig. 6 A). Oscula not observed on preserved specimens but from internal structure located on the apices of fistulae. Sponge surface hispid with spicules projecting up to 1 mm above surface surrounding papillae; fistulae microhispid, with spicules projecting less than 100 µm above surface. Main body of sponge papillose. Consistency woody, not compressible. Colour of main sponge body in alcohol brown; fistulae lighter shade of brown.

Microscopic features. Cortex 0.7 mm thick with small amount of collagen. Fistulae either inhalant or exhalant; exhalant canals 200 to 400 µm diameter. Choanosomal principal multispicular tracts packed tightly with spicules held by only small amount of spongin cementing tracts; tracts composed of styles to strongloxeas, oriented with heads toward base; tracks originating at base of sponge, extending toward surface or penetrating it (Fig. 7 A). Principal multispicular tracts carrying up through fistulae, slightly penetrating surface. Multispicular tracts surrounding central exhalant canal. Subtylostyles to tylostyles scattered randomly throughout cortex and choanosome.

Spicules. Spicules of three types: 1) abundant straight styles to strongloxeas (Fig. 7 B) composing principal spicule tracts; 2) less abundant subtylostyles to tylostyles (Fig. 7 C) with long sharp points, some subtylote, vaguely fusiform, straight or slightly curved; 3) very thin, raphide-like spicules (Fig. 7 D) with a single recurved spine at one end, visible only by SEM. Spicule measurements are from the one specimen examined.

KML 1020 Remarks. Koltun (1962) described Polymastia kurilensis from the Kurile Islands. It has the same spicule types and similar sizes as our specimen. The thin, recurved-spined spicules are characteristic and have not been reported for any other North Pacific species of Polymastia. As noted above, the recurved spines are only visible under high magnification with a light microscope or by SEM. The only other North Pacific Polymastia with a cushion-like form and a few wart-like fistulae is P. laganoides Lambe 1895. But this species does not have recurved-spined spicules and spicules ranging from styles to tylostyles. Given the characteristic recurved-spined spicules, a similar spicule complement, similar form, and a sample depth of 126 m for our specimen, compared to the reported distribution range of 50 to 301 m for P. kurilensis, we conclude that our specimen belongs to this species.

Bathymetric range. Depth range 50 to 301 m.

Geographic distribution. Range extension from the Kurile Islands, the Okhotsk Sea (Kamchatka Peninsula, Russia) and Bering Sea east to Kodiak I. (AK, USA).