Hyalopomatus jirkovi Kupriyanova 1993

Hyalopomatus jirkovi Kupriyanova, 1993a

(Fig. 5 A–B, H)

Hyalopomatus jirkovi Kupriyanova, 1993a: 147 –148, fig. 1.

Material examined. Type material. SIO: R/V “ Vityaz ” Stn. 5593, 45 °38’N, 152°02’E, 1050 m, 12 Aug 1966 (holotype and paratype).

Newly examined material. SIO: R/V “ Vityaz ” Stn. 4131, 55 º47.6’N, 145º19.7’W, 3949 m, trawl, 9 Nov 1958 (4 specs).

Description. Tube: Tubes white, smooth, attached to the Cidaris throughout its length, circular in cross-section, some indication of interruptions in calcium carbonate secretion (see Sanfilippo 2009) along the tube.

Branchial crown: 8–10 pairs of radioles, not joined by inter-radiolar membrane. Bases of branchial radioles short. 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. Constriction present. Pair of lateral wings proximal to opercular bulb and pseudoperculum absent.

Operculum: semi-transparent elongated vesicle with slightly differentiated darker distal cap (Fig. 5 H).

Collar and thoracic membranes: collar four-lobed, with ventral lobe additionally sub-divided into two round lobes by a deep incision; ventro-lateral lobes twice as long as latero-dorsal lobes (Fig. 5 A, B). Thoracic membranes reaching up to 3rd chaetiger, of even width throughout (Fig. 5 A, B).

Thorax: with six thoracic chaetigers, five of which uncinigerous (Fig. 5 A, B). Collar chaetae simple capillaries and special fin-and-blade chaetae, with wide blade continuing without a gap in proximal fin made of numerous small teeth. Remaining notochaetae with short wide distal limbate blade. Apomatus chaetae absent. Thoracic uncini rasp-shaped, with about 20 teeth in profile view, arranged in 3–4 transverse rows, and with elongated and flattened anterior peg (SEM details of peg structure not available).

Abdomen: abdominal uncini similar to thoracic uncini but smaller with about 20 teeth in profile view. Straight, almost capillary (distal limbation very narrow) abdominal chaetae (SEM details not available).

Colour: unknown.

Remarks. This is the second record of this species previously known only from two specimens (the type material) collected from the Kurile-Kamchatka Trench. Hyalopomatus jirkovi clearly differs from all described species of Hyalopomatus by the structure of the collar with ventral lobe sub-divided into two lobes by deep incision at midline.

Distribution. Kurile-Kamchatka Trench, Gulf of Alaska, 1050–3949 m.