Bathyvermilia challengeri Zibrowius, 1973

(Fig. 4)

Placostegus ornatus McIntosh, 1885: 522 –524, pl. 55, fig. 5–6, pl. 30A, fig. 25–27. Bathyvermilia challengeri Zibrowius, 1973: 428 –430, fig. 1a-e.

Material examined. Newly examined material. SIO: R/V “ Vityaz ” Stn. 3156, 39 º57’N, 165º07.8’E, 5535 m, trawl, 28 Sept 1954 (1 tube); Stn. 3499, 25 º27.1’N, 143º22’E, 4892-5022 m (1 spec.); Stn. 6334, 11 º06.2’S, 159º99’W, 5240-5300 m, trawl, 31 Jul 1970 (1 spec.).

Additional material. BPBM: Acc. No. 1983.252, 16 °41.5’N, 169°34.3’W, Johnston Atoll, 380 m, Hawaii Undersea Research Laboratory (HURL) submersible dive 83–208 (1 spec.).

Description. Tube: white opaque, about 0.8 mm in diameter (portion shown in Fig. 4 A, B 27 mm long), with very regularly closely arranged smooth transverse ridges; longitudinal groove cutting transverse ridges (Fig. 4 A, B).

Branchial crown: with ten pairs of radioles not joined by inter-radiolar membrane. Branchial eyes not visible in preserved material. Stylodes absent.

Peduncle: inserted as dorsal 2nd radiole, about same thickness as rest of radioles, smooth, circular in cross-section (Fig. 4 C); slightly enlarged at base of operculum; constriction present. Pair of lateral wings proximal to opercular bulb and pseudoperculum absent.

Operculum: inverted conical, slightly longer than wide, with simple almost flat calcareous distal plate (Fig. 4 C) about 1 mm in diameter (specimen from Stn. 6334 with a calcareous granule inside operculum).

Collar and thoracic membranes: collar trilobed. Thoracic membranes reaching up to 4th chaetiger.

Thorax: with seven thoracic chaetigers, six of which uncinigerous (Fig. 4 D). Collar chaetae simple longer limbate (Fig. 4 E) and shorter capillaries with poorly discernable limbate blade (Fig. 4 F), special chaetae absent. Apomatus chaetae present (Fig. 4 G). Uncini saw-shaped with seven-eight teeth (Fig. 4 I) and simple pointed anterior peg (SEM details not available).

Abdomen: anterior abdominal uncini similar to thoracic ones, but smaller (Fig. 4 J, SEM details not available), posterior rasp-shaped (Fig. 4 K). Chaetae flat narrow geniculate with blunt teeth (Fig. 4 H, SEM details not available) anteriorly and long slender capillaries posteriorly (Fig. 4 I, SEM details not available).

Size: body 6 mm long, branchial crown 7 mm long.

Colour: unknown.

Distribution. Mid-Pacific Ocean, 4246–5719 m, and Johnston Atoll (about 1400 km west of Hawaii), 380 m.

Remarks. This species has a very characteristic tube with numerous, close to each other, conspicuous transverse ridges (not anteriorly directed peristomes) encircling the tube interrupted by a longitudinal groove cutting transverse ridges near the base. Zibrowius (1973) mentions that the thoracic membranes in the type material are very short, ending at about 2nd chaetiger, however, the material is in such poor state of preservation that the details of collar structure remain unknown.

Previous records of this species came from three R/V “ Challenger ” stations in the North and South Pacific Ocean at 4246–5719 m (Zibrowius 1973). The specimen collected off Johnston Atoll near Hawaii is currently the shallowest record for this species. Although the specimen from the upper bathyal off Johnston Atoll fits the original description of B. challengeri and is morphologically very similar to the specimens collected from the lower abyssal zone, such a disjunct bathymetric distribution is unusual. Further collecting and additional taxonomic studies of deep-sea serpulids are needed to determine whether B. challengeri does have disjunct or wide bathymetric distribution or whether at least two morphologically similar species are present in the Pacific.