Endoxocrinus (Diplocrinus) maclearanus ( Thomson, 1872b )

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 : 38-39

Endoxocrinus (Diplocrinus) maclearanus ( Thomson, 1872b)

Figures 4 a, 5d, 19d, 20c.

Synonymy: Pentacrinus maclearanus Thomson, 1872: 123 ; Pentacrinus maclearanus Carpenter, 1884: 312 ; Pentacrinus mülleri Carpenter, 1884 (pars): 311; Isocrinus maclearanus Döderlein, 1907: 19 ; Cenocrinus (Diplocrinus) maclearanus Döderlein, 1912: 20 –21; Diplocrinus maclearanus A.H. Clark, 1923: 11 ; Diplocrinus (Diplocrinus) maclearanus Roux, 1977: 64 ; Endoxocrinus maclearanus Rasmussen & Sievertz­Doreck, 1978 : T857; Endoxocrinus (Diplocrinus) maclearanus David, 1998: 203 (unpublished data) and Roux et al., 2002: 820.

Emended diagnosis

A species of the subgenus Diplocrinus with 14–30 smooth arms up to 10 cm long; brachials relatively low; proximal synostoses at Br1+2 relatively flat with syzygial stereom irregularly developed and with axial lumen rectangular; number of internodals per mature noditaxis usually 6–14 (mode in local populations 8–12); stalk shorter than arms, <9 cm long (mean 3.8 cm), and pentalobate to pentagonal in cross section; columnal thickness and width strongly irregular; proximalmost stalk diameter up to 5.1 mm; frequent strong symmorphy in symplexies; cirri usually 5 per whorl, sometimes 1–4, oriented upward; cryptosymplexies with undulating symmorphic surface, synostosial stereom predominating on interpetaloid zones, and axial canal filled with short thick spicules clearly separated from perilumen; secondary lumen small or absent.

Type locality

Off Brazil (Pernambuco) at a depth of 640 m.

Holotype: Catalogue no. 3.30.21, Natural History Museum, London; first figured by Thomson 1872, reprinted by Carpenter 1884, Pl. 16, Fig. 1 .

Occurence

Western tropical Atlantic from the Blake Plateau to eastern Brazil (Barra Grande), at depths from 432 m to 878 m; Blake Plateau (depth 635–878 m), northwestern Bahamas (depth 512–805 m), northeastern Puerto Rico and Lesser Antilles (depth 432–476 m). The wider depth range (187–604 m, possible 154–910 m) given by Meyer et al. (1978) results from the inclusion of E. (E.) carolinae into D. maclearanus , and the erroneous attribution of a few E. parrae specimens to this species (Tomassi 1969).

Remarks

The holotype, dredged by the Challenger off the eastern end of Brazil (Barra Grande) at a depth of 640 m, has the greatest number of arms (30); other specimens with a similar proximalmost stalk diameter have up to 27 arms. David (1998) distinguished specimens other than the holotype as E. (D.) maclearanus variety minimus. As argued above, we treat this phenotype as a dwarf infrasubspecific variant characteristic of populations such as those of the Bahamian lithoherms. Currently, statistical analyses cannot distinguish two phenotypes or subspecies of E. (D.) maclearanus using characters other than size.

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 4. The four phenotypes of diplocrinine crinoids in their environment off the Bahamas. (a): population of the minimus phenotype on the flank of a lithoherm (photo courtesy A. C. Neumann, Univ. North Carolina, taken from DSV Alvin), (b): one specimen of the prionodes phenotype between blocks at the Deep site, (c): a population of the parrae phenotype accompanied by a few Neocrinus decorus on the upcurrent slope of a large mound at the Middle Site, (d): one specimen of the parrae phenotype on a hardground slope at the Middle Site, (e): a population of the carolinae phenotype clinging to the overhanging edge of a block at the Deep Site, (f): three specimens of the phenotype carolinae attached to the side of a block at the Deep Site (photos b­f taken from Johnson Sea Link by C. G. Messing).