Figs 1 A–G
Synonymy: Bathycrinus sp. B. — Belyaev 1966: 118, 119, fig. 31; Bathycrinus volubilis –Mironov 2000: 714–719, figs 2–4. Non: Bathycrinus ? volubilis — Mironov 2000: 718, St. 3514 (= Bathycrinus sp. cf. B. longipinnus n. sp., see below).
Holotype. IO RAS No. XV-63-1, RV Vityaz, St. 5612, 26.07.1966, aboral cup with arms and stalk, RRD = 2.6 mm.
Type locality. RV Vityaz, cruise 39, St. 5612, 26.07.1966, TS, Kuril-Kamchatka Trench, 45º 25′ N, 153º07′ E, 8185–8400 m.
Material examined. RV Sonne 250, KuramBio II, St. 52,EBS, 0 6.09.2016, 45°29.77′ N, 153°12.16′ E – 45°29.18′ N, 153°11.13′ E, 8737 m, 1 specimen, SMF; RV Sonne 250, KuramBio II, St. 77, EBS, 13.09.2016, 45°13.71′ N 152°51.21′ E E– 45°14.21′ N 152°49.95′ E, 9584 m, 2 spms, SMF; RV Sonne 250, Expedition KuramBio II, St. 78, AGT, 13.09.2016, 45°13.979′ N, 152°48.980′ E – 45°14.482′ N, 152°47.736′ E, 9581.7– 9581.3 m, 50 spms, SMF; RV Sonne 250, KuramBio II, St. 103, AGT, 21.09.2016, 44°12.499′ N, 150°39.035′ E – 44°12.502′ N, 150°37.258′ E, 9292.9–9430.8 m, fragments of the stalks, SMF. RV Vityaz, cruise 14, St. 2217, 29. VI.1953, TS, 44°08′ N, 150°32′ E, 9000–9050 m, 90 spms, IO RAS Cat. no. Ech 00717– Ech 00720; RV Vityaz, cruise 19, St. 3176, 0 6.10.1954, TS, 44°08.5′ N, 150°22.0′ E, 8175– 8840 m, 35 spms, IO RAS Cat. no Ech 00721–723; RV Vityaz, cruise 22, RV Vityaz, cruise 39, St. 5612, TS, 26.07.1966, 45°25′ N, 153°07′ E, 8185–8400 m, 254 spms, IO RAS Cat. no. Ech 00724– Ech 00731; RV Vityaz, cruise 39, St. 5631, TG, 0 4.09.1966, 43°47′ N, 149°43′ E, 9070–9345 m, 4 spms, IO RAS Cat. no. Ech 00732; RV Vityaz, cruise 39, St. 5632, TG, 0 5.09.1966, 43°44′ N, 149°52′ E, 8240–8345 m, 1 sp., IO RAS Cat. no. Ech00733. Total: 438 specimens from the Kuril-Kamchatka Trench; most of them represented by aboral cup with proximal arms and proxistele, upper diameter of RR-rings (RRD) from 1.4 to 3.7 mm.
Remarks. Original detailed description of Bathycrinus volubilis was based on abundant material (Mironov 2000). Here I give some additional information on intra-species variability. Both BB-ring and RR-ring always strongly pentalobate (quinquelobate) in cross section (Fig. 1 A–B). Numerous small plates of different shape on sides of upper tegmen (Fig.1C). Proximal arm pattern and position of P1 were examined on 216 arms (Table 1); 49 different proximal patterns were found. Among them, 32 different cases were observed once only. Most frequent proximal patterns are 1+2 4+5 7+8 10+11 13 (41%) and 1+2 4+5 7+8 10+11 12 (20%). P1 on Brs 11–15; the most frequent positions on Br12 (31%) and Br11 (24%). Cover plates shape changes from proximal to distal arm. The cover plates on the proximal Brs are usually thick (not flattened) and with rough surface (Fig. 1D). On the Brs 4–12 they display two series of rough protuberances. The cover plates on distal Brs and pinnules are thin with a smooth surface (Fig. 1F). The number of short columnals forming the proxistele varies from 17 to 69, but in specimens from St. 2217 it varies from 5 to 24; This number does not exceed 31 in the other Bathycrinus species. Knobby processes on IBrs 1–2 are always absent.
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Distribution. Kuril-Kamchatka Trench, 8175–9584 m. A specimen from the Izu-Bonin Trench (RV Vityaz, St. 3514) identified as Bathycrinus ? volubilis (Mironov 2000) is referred herein to Bathycrinus sp. cf. B. longipinnus n. sp.