Bathycrinus cf. aldrichianus Wyville Thomson, 1876

Bohn, Jens Michael, 2006, Crinoidea and Holothuroidea (Echinodermata) of the abyssal Angola Basin — Results of the DIVA­ 1 expedition of FS " Meteor " (Cruise M 48 / 1), Zootaxa 1276, pp. 1-31 : 7-8

Bathycrinus cf. aldrichianus Wyville Thomson, 1876

(Figs 2A, 3)

Bathycrinus aldrichianus Wyville Thomson, 1876: 47 –51, fig. 1; Clark, 1977: 159 –162, fig. 1 (g) [synonymy]

Bathycrinus campbellianus P.H. Carpenter, 1884: 238 –240, fig. 15 Bathycrinus serratus A.H. Clark, 1908: 205 –207, fig. 1

Material. M 48/1­344: 1 calyx ( ZSM 20043086).

Description. The specimen is small and damaged, only the radials and arms (up to Br10) are preserved, the basals and the stalk are missing (Fig. 2A). The calyx is about 1.7 mm wide. The five radials are smooth, about 0.7 mm high, have a proximal width of 0.5 mm and a distal width of 0.8 mm. Sharp­edged lateral flanges and a prominent crestlike keel characterise the first brachitaxis (IBr1 and IBr2) and the proximal brachials. On the axillaries (IBr2) the keel is Y­shaped. In distal brachials the lateral flanges disappear and the crest­like keel is less prominent. The first brachitaxis is about 1.8 mm long and at the joint of IBr1 and IBr2 0.9 mm wide. Though indistinct, the first non­muscular joints are between brachials 1+2, 4+5 and 7+8. No pinnules were found (not developed yet?).

Remarks. Currently, there are two Atlantic Bathycrinus species recognized, viz B. aldrichianus Wyville Thomson, 1876 and B. gracilis Wyville Thomson, 1872 which both are similar in being "very serrated in profile" in contrast to the remaining Atlantic species which have "smooth and rounded ossicles and profiles" ( Clark 1977: p. 167). The current specimen corresponds with both species in the ornamentation of the first brachitaxis and the proximal brachials, with a central keel and lateral flanges ( Clark 1977, 1980; Macurda & Meyer 1976). Slight differences in the specificity of the ornamentation may be correlated with size ( Clark 1977) and thus not sufficient to separate both species. The only character known to distinguish both species seems to be the position of the first pinnule on the arm. Bathycrinus gracilis has the first pinnule on brachials 10 to 12, while B. aldrichianus has the first pinnule on brachials 8 to 11 ( Clark 1980). Due to the fact that the current specimen lacks pinnules, a reliable determination is not possible and the specimen is tentatively assigned to B. aldrichianus because of the geographical vicinity to other records of this species.

Distribution. Bathycrinus aldrichianus has been described from the north­western, the central and the southern Atlantic Ocean ( Fig. 3 ), 3305–5860 m ( Carpenter 1884; Clark 1908; Clark 1977; Gislén 1951; Macurda & Meyer 1976; herein), whereas B. gracilis seems to be restricted to the north­eastern Atlantic Ocean ( Fig. 3 ), 2880–5330 m ( Carpenter 1884; Clark 1977, 1980; Harvey et al. 1988; IFREMER BIOCEAN; Koehler 1909).

FIGURE 2. (A) Bathycrinus cf. aldrichianus Wyville Thomson, 1876 . Distal part of calyx with arms, basals and stalk missing (IBr1, IBr2 —first and second brachials of first brachitaxis). (B–E) Psychropotes semperiana Théel, 1882 . Calcareous deposits. (B) Large crosses (damaged) from dorsal body wall, with four arms, central apophysis and downwardly bent hooks. (C) Large crosses (damaged) from dorsal body wall, with four arms and central apophysis (arrowheads). (D) Small crosses from dorsal body wall. (E) Rods and crosses from ventral body wall.

Figures

FIGURE 3. Distribution of Bathycrinus aldrichianus Wyville Thomson, 1876 and the closely related B. gracilis Wyville Thomson, 1872. Questionable records for B. aldrichianus, often based on stalk fragments solely, are indicated as blank circles.