Hyalopomatus sikorskii Kupriyanova 1993

Hyalopomatus sikorskii Kupriyanova, 1993a

(Fig. 5 C–F, G)

Hyalopomatus sikorskii Kupriyanova, 1993a: 150 –152, fig. 3.

Material examined. Type material. SIO: R/V “ Vityaz ” Stn. 2116, 45 °16’N, 156°13’E, 4550 m, 21 May 1953 (2 paratypes and holotype).

Newly examined material. SIO: R/V “ Vityaz ” Stn. 3520, 28 º53.5’N, 137º21.1’E, 4150– 4000 m, trawl, rock, soft chips made of a number of siliceous spicules stuck together, 24 Oct 1955 (2 specs).

Description. Tube: white, circular or semi-circular in cross-section, attached to the substrate throughout its length, very fragile. Tube surface rough with weak traces of growth rings. Peristomes, longitudinal keels, and ringlike thickenings all absent.

Branchial crown: six pairs of radioles not joined by inter-radiolar membrane. Radioles with long naked tips. Branchial eyes not visible in preserved material. Stylodes absent.

Peduncle: inserted as 1st dorsal radiole on left side of crown, thin, smooth, circular in cross-section, with several constrictions at opercular base. Pair of lateral wings proximal to opercular bulb and pseudoperculum absent.

Operculum: elongated, subdivided into two parts of about same size: proximal part semi-transparent soft vesicle, and distal part with distinct darker endplate resembling a brimless domed hat (Fig. 5 C, D, G).

Collar and thoracic membranes: collar short, trilobed, with small and narrow lateral lobes shifted dorsally, and big and wide ventral lobe. Thoracic membranes reaching up to 3rd chaetiger, of even width throughout (Fig. 5 E, F).

Thorax: with six thoracic chaetigers, five of which uncinigerous (Fig. 5 E, F). Collar chaetae limbate capillaries and special fin-and-blade chaetae with distal blade continuing without a gap into proximal fin made of numerous small teeth. Remaining notochaetae capillaries with short distal limbate blade. Apomatus chaetae absent. Thoracic uncini rasp-shaped, with 20–25 teeth in profile view, arranged in 2–3 transverse rows (SEM details of uncinal pegs not available).

Abdomen: abdominal uncini similar to thoracic ones (SEM details of uncinal pegs not available). Abdominal chaetae long, straight, almost capillary, with short tip made of fine teeth (SEM details not available).

Colour: unknown.

Distribution. Kurile-Kamchatka Trench, North Pacific Ocean south of Japan, 4000–4550 m.

Remarks. This is the second record of this species that was previously known only from three specimens collected in the Kurile-Kamchatka Trench. Hyalopomatus sikorskii differs from the other species of this genus by its