(Figs. 6, 7)
Bathyvermilia zibrowiusi Kupriyanova, 1993 b: 23 –25, fig. 2, ten Hove & Kupriyanova 2009: 32 (name only).
Material examined. Type material. SIO: R/V “ Vityaz ” Stn. 2116, 45 ° 16 ’N, 156 ° 13 ’E, 4550 m, 21 May 1953 (holotype).
Newly examined material. SIO: R/V “ Vityaz ”, Stn. 6106, 58 º 15 ’N, 142 º 34 ’W, 3620 m, trawl, 13 May 1969 (4 specs).
Comparative material. Bathyvermilia kupriyanovae Bastida-Zavala, 2008, NHMLAC: Poly 2181, holotype; Poly 2182, 13 paratypes.
Description. Tube: white, round in cross section, with smooth shiny surface (=outer hyaline layer present), with wide peristomes along entire length of tube, distance between peristomes decreasing towards distal end of tube (Fig. 6 A). Tube entrance usually widened into peristome. Tube attached to substrate only at base.
Branchial crown: 18–20 pairs of radioles not joined by inter-radiolar membrane and without long naked tips. Branchial eyes not visible in preserved material. Stylodes absent.
Peduncle: inserted between 1 st and 2 nd dorsal radioles, slightly below bases of radioles, about 1.5 times as thick as radioles, smooth, circular in cross-section (Fig. 6 B). Pair of lateral wings proximal to opercular bulb absent.
Operculum: conical, covered with flat brown chitinous endplate about 1.7 mm in diameter, with one concentric ridge and central dome; separated from peduncle by conspicuous constriction (Fig. 6 B–D). Pseudoperculum absent.
Collar and thoracic membranes: short collar with straight margin, not covering bases of radioles, not subdivided into lobes (= unlobed), of equal length all around. Thoracic membranes reaching up to the 4 th chaetiger; wide until 2 nd chaetiger, then narrowing abruptly.
Thorax: with seven thoracic segments, six of which uncinigerous. Collar chaetae limbate capillaries similar to those of thoracic chaetigers (Fig. 7 A), special collar chaetae absent. Apomatus chaetae present (Fig. 7 B). Sawshaped thoracic uncini with six teeth above pointed anterior fang (Fig. 7 C).
Abdomen: uncini similar to thoracic ones, but smaller and with teeth arranged in two rows above simple, distally rounded anterior peg (Fig. 7 D). Chaetae flat geniculate, with rounded teeth (Fig. 7 E).
Size: body up to 16 mm long, branchial crown length up to 7 mm.
Colour: unknown.
Distribution. Kurile-Kamchatka Trench, Aleutian Trench, 3610–4550 m.
Remarks. This is the second record of this species previously known only from a single specimen (the holotype) collected from the Kurile-Kamchatka. Bathyvermilia zibrowiusi clearly differs from B. challengeri Zibrowius, 1973 (see above) by the details of the tube structure, the wide flaring peristomes at the distal end of the tube in the former and marked transverse ridges (not anteriorly directed peristomes) encircling the tube in the latter. The opercular endplate of B. zibrowiusi is chitinous, without calcareous deposits, whereas in B. challengeri the endplate is completely covered by a flat calcareous deposit. In addition, the thoracic membranes of Bathyvermilia zibrowiusi extend to the 4 th chaetiger, but they are supposedly much shorter in B. challengeri reaching up to the 2 nd chaetiger according to the original description (Zibrowius 1973). However, this character is unreliable (see above) as in the material of B. challengeri examined here thoracic membranes also reach the 4 th chaetiger.
Bathyvermilia langerhansi (Fauvel, 1909), known from the Atlantic, has tubes with longitudinal keels (but lacking peristomes and transverse ridges), distal chitinous endplate encrusted with calcareous deposits, and thoracic membranes ending at the 3 rd chaetiger. Bathyvermilia islandica Sanfilippo, 2001 known from Iceland has long thoracic membranes ending at the 7 th chaetiger and tube with undulating peristomes. Sanfilippo (2001) provided a key to all four species of Bathyvermilia known at that time. Bathyvermilia eliasoni (recently transferred from Vermiliopis by Kupriyanova & Nishi 2010) also has very characteristic tube with three denticulate longitudinal keels (Fig. 5 I).
Bathyvermilia zibrowiusi appears to be most similar to the recently described B. kupriyanovae Bastida-Zavala, 2008 that also has tubes with wide peristomes and thoracic membranes extending to the 4 th chaetiger. Bastida-Zavala (2008) stated that the main differences between the two species is in the distal opercular plate with developed concentric ridges in B. zibrowiusi, as opposed to simple chitinous endplate with some calcareous inclusions in B. kupriyanovae. Other differences between these species are rather subtle (and likely unreliable), such as smooth versus wrinkled sides of opercula and relative thickness of the opercular peduncles and radioles.