Endoxocrinus (Diplocrinus) alternicirrus ( Carpenter, 1882 )

David, Jerome, Roux, Michel, Messing, Charles G. & Ameziane, Nadia, 2006, Revision of the pentacrinid stalked crinoids of the genus Endoxocrinus (Echinodermata, Crinoidea), with a study of environmental control of characters and its consequences for taxonomy, Zootaxa 1156, pp. 1-50 : 40-41

Endoxocrinus (Diplocrinus) alternicirrus ( Carpenter, 1882)

Figures 13 , 19 c, 20b.

Synonymy: Pentacrinus alternicirra Carpenter 1882: 167 ; Pentacrinus alternicirrus Carpenter, 1884: 321 ; Isocrinus sibogae Döderlein, 1907: 18 ; Endoxocrinus alternicirrus A.H. Clark, 1908b: 151 ; Endoxocrinus sibogae A. H. Clark, 1908b: 152 ; Cenocrinus (Diplocrinus) alternicirrus Döderlein, 1912: 20 –21; Cenocrinus (Diplocrinus) sibogae Döderlein, 1912: 20 –21; Diplocrinus alternicirrus A.H. Clark, 1923: 11 ; Diplocrinus sibogae A.H. Clark, 1923: 11 ; Diplocrinus alternicirrus Roux, 1977: 45 ; Endoxocrinus alternicirrus Rasmussen & Sievertz­ Doreck, 1978: T857; Diplocrinus (Diplocrinus) alternicirrus Roux, 1980: 119 ; Diplocrinus aff. sibogae Bourseau & Roux, 1989: 158 ; Diplocrinus (Diplocrinus) sibogae Bourseau et al., 1991: 259 ; Endoxocrinus (Diplocrinus) alternicirrus David, 1998: 203 (unpublished data), Roux et al., 2002: 820; Endoxocrinus (Diplocrinus) sibogae Roux et al., 2002: 820 .

Emended diagnosis

A species of the subgenus Diplocrinus with arm number variable, up to 64 in largest specimens; arms usually smooth, up to 15.3 mm long (usually 10–12 cm); synostosis at IBr1+2 relatively flat with synostosial stereom predominating, but with a small syzygial crenulation near aboral edge of facet; axial canal rectangular; stalk length variable, up to 14 cm, usually <10 cm; number of internodals per mature noditaxis 4–10, usually 5–6; adult stalk stellate to pentagonal in cross section; columnals heterometric; proximalmost diameter of stalk usually 4–6 mm, up to 7.9 mm in largest specimens; frequently less than 5 cirri per nodal; proximal cirri oriented downward; cirrus sockets nearly circular, relatively large; cirrals relatively long, number of cirrals per cirrus up to 35, usually 28–30; cirri remaining rudimentary usually before the 5th nodal; interpetaloid zone of cryptosymplexies with syzygial stereom predominating but with strong symmorphy in inner portion; axial canal filled with long thin spicules clearly distinct from perilumen; no secondary lumen.

Type locality

Off Meangis (now Miangas) Island, north of Sulawesi, Indonesia. Holotype: Catalogue no. 1885.3.30.22, Natural History Museum, London; first figured by Carpenter 1884, Pl. 25, Fig. 1 .

Occurrence

Central to western Pacific at depths from 364 m to 1476 m: from Tasmania to Japan (Okinawa, Ryukyu Islands), including Tahiti and Hawaii ( Roux 1980; Kogo 1998; David 1998; Améziane et al. in press).

Remarks

Here, we maintain the distinction between alternicirrus and sibogae and place them at subspecific rank. However, we currently have no evidence of ecological or geographical isolation, and their depth ranges show a large overlap. So, their subspecific status is less well documented than for the subspecies of E. (E.) parrae . Additional specimens, and especially the discovery of a single population with both the two typical phenotypes and intermediate morphologies without bimodal statistical distribution, could demonstrate that E. (D.) alternicirrus sibogae and E. (D.) alternicirrus represent a single species with a wide unimodal field of variation, as in E. (D.) wyvillethomsoni .

Included subspecies

Pentacrinus alternicirrus Carpenter, 1882 ; Isocrinus sibogae Döderlein, 1907 .

Figures

FIGURE 1. Morphology of diplocrinine crinoids. General external morphology (a), and proximal portion of the stalk and crown showing isotomy (b) or endotomy (c) of arm branching. Facet of the symplexial articulation between columnals (d), and detailed portion of the heteromorphic stalk (e).

FIGURE 13. Pacific phenotypes. Specimens from New Caledonia. a and b: alternicirrus phenotype, a: specimen BC 3, b: stalk of specimen TA 20; c and d: sibogae phenotype, specimen BE 8.

FIGURE 19. Distal facet of nodals (cryptosymplexies) identifying the four species of Endoxocrinus. (a): E. (E.) parrae, (b): E. (D.) wyvillethomsoni, (c): E. (D.) alternicirrus, (d): E. (D.) maclearanus.