Bathycrinus australis A.H. Clark 1907

Bathycrinus australis A.H. Clark, 1907b

Figure 2; Tables 2–3.

Synonymy: Bathycrinus aldrichianus Carpenter, 1884: 241 –243, pl. 7, pl. 7a (figs. 1–21), pl. 7b, pl. 8a (figs 4–5); Bathycrinus australis A.H. Clark, 1907b: 553 –554; Döderlein, 1912: 9–10, pl. 5 (fig. 1), pl. 6 (fig. 7); Ilycrinus australis A.H. Clark, 1915: 154 –155; Vaney & John, 1939: 661; Bathycrinus australis Gislén, 1938: 16; 1956: 61–62, pl. 1 (figs. 1–6); Mc Knight, 1973: 204–205; A.M. Clark, 1977: 162–164; Bathycrinus cf. aldrichianus Bohn, 2006: 7 –9, fig. 2A; Bathycrinus australis Mironov, 2008: 141,143.

Material examined. External morphological features of specimens examined (Table 2) fall within the range of variation described by A.M. Clark (1977), especially with a flared radial ring and smooth flanged arms (Fig. 2 A–B). Bohn (2006) reported only stalk fragments and a single incomplete juvenile crown from DIVA stations and attributed them to B. cf. aldrichianus mainly on biogeographical evidence. These specimens are attributed here to B. australis based the analysis of their stalk articulations.

Description of stalk articulations. The distal end of the stalk varies from several fused columnals bearing radicules that penetrate soft sediment (Fig. 2 C) to robust ramification that encrust rocks or pebbles (Fig. 2 E). Usually, the transition is gradual (Fig. 2 D) between the mesistele which has columnals significantly higher than wide (ratio height to maximum diameter> 3 in mid mesistele), and the dististele in which columnals are nearly as high as wide (Fig. 2 C, E). In the largest specimens, distal synarthries have a large extension of deep ligament fossae; each segment of the fulcral ridge is bottle-shaped and has two rows of 35–40 small crenulae underlining its axis (Fig. 2 F–G). In the dististele of young specimens, synarthries resemble those of B. aldrichianus (Fig. 2 H). Mesistele synarthries are well developed in juveniles and have larger and deeper ligamentary depressions (Fig. 2 K–L), and medium-sized specimens have strongly rounded oval facets with the longest diameter perpendicular to the fulcral ridge. As growth increases, the fulcral ridge becomes relatively narrower around axial canal with convex lateral sides (Fig. 2 I–J). Stalk articulations in B. australis and B. aldrichianus differ significantly, especially in their mesistele synarthries.

Occurrence. B. australis occurs in the South Atlantic with northern records from the deep Argentina plateau and Angola basin. It is also known from the Southern Ocean and the southern Indian Ocean from east of the Antarctic Peninsula to the Kermadec Trench and New Zealand (Tables 2–3). The depth range is large and extends from 1525 m to 8210 m, possibly from 1488 to 8300 m.

cruises. *: after Bohn (2006).

Scotia 62°10’S – 41°20’W 3246 Vaney & John, 1939 1 specimen