Porphyrocrinus cf. incrassatus ( Gislén, 1933 ), Gislen, 1933

Eléaume, Marc, Bohn, Jens-Michael, Roux, Michel & Améziane, Nadia, 2012, Stalked crinoids (Echinodermata) collected by the R / V Polarstern and Meteor in the south Atlantic and in Antarctica, Zootaxa 3425, pp. 1-22 : 17-18

Porphyrocrinus cf. incrassatus ( Gislén, 1933)

Figure 10 ; Table 5 .

Synonymy: Porphyrocrinus cf. incrassatus Roux, 1980b: 904 .

Material examined ( Table 5 ). One distal stalk fragment (Bavarian State Museum Collection of Zoology in Munich, catalogue number ZSM 20070046) was dredged in the Cape Basin during R/V Meteor cruise DIVA II. One specimen which had been cited ( Roux 1980b) but not described is housed in the collections of the Muséum national d’Histoire naturelle, Paris (catalogue number MNHN IE- 2012-760). It was dredged by N/O Jean Charcot during the French cruise “Walvis I” (station DS01) at the south-eastern foot of the Walvis ridge.

Description. Walvis specimen: proximal stalk, aboral cup and proximal crown ( Fig. 10 A). Aboral cup of maximum height 1.9 mm with radial ring more flared than basal ring ( Fig. 10 B); diameter at basal/stalk junction 1.4 mm, at radial/basal sutures 1.6 mm, at upper radial border 2.3 mm, maximum basal height 0.9 mm, maximum radial height 1.1 mm; ratio of radial to basal height 1.2; five basals with conspicuous sutures. One arm preserved to Br9 (length 0.96 mm) with first pinnule on Br8, two arms to Br4, one to Br5, and fifth restricted to Br1+2; arm pattern with successive brachial pairs; all brachials constricted at mid height; muscular articulations larger than synostoses ( Fig. 10 C). Preserved stalk length 14.1 mm with 15 subcylindrical columnals and diameter at broken end 0.98 mm; proxistele of five columnals united by non-functional articulations; height of proximalmost columnal 0.4 mm, height of distalmost preserved columnal 1.16 mm (ratio of height to diameter 1.2); beyond proxistele, columnals articulated by synarthries with circular facet with 8-shaped deep ligamentary pit and short fulcral ridges of 6–7 small crenulae on each side ( Fig. 10 D–E).

Incomplete stalk from Cape Basin: length 57 mm, mesistele only, with proximal part of circular joints missing; diameter at fulcral ridge axis 0.8 mm proximally and 1.04 mm distally, columnal height respectively 3.5 mm and 4.3 mm with ratio of height to diameter 4.4 and 4.1. All articulations are synarthries with areolar depression and fulcral ridge more developed at distal than at proximal end ( Fig. 10 F–G). This stalk fragment belongs to a specimen smaller than the Walvis one.

Remarks. The Walvis P. cf. incrassatus and Hydrosnake P. incrassatus are both about 1.75 larger than the holotype of P. incrassatus from Saint Helena ( Gislén 1933) and the largest Thalassa specimens from the Bay of Biscay ( Roux 1977). The Walvis specimen is the only one that retains the proximal crown. It differs from the Hydrosnake specimen in having shorter radials and fewer proximal columnals although these differences may be due to its larger size or to intraspecific variations. Such wide range of variation in external morphology was also observed ( Messing 2007) in the Indo-Pacific species P. verrocosus Gislén, 1925 (= P. polyarthra A.M. Clark, 1973 ). This species is larger with short brachials not constricted at mid height, and lives at significantly shallower depths (218–400 m). Therefore, the Walvis and Cape Basin specimens are not interpreted as juvenile specimens of P. verrucosus . They lived at greater depth (more than 5000 m) than the other specimens of P. incrassatus (<3000 m). As a complete specimen of P. incrassatus has not yet been found, the attribution of specimens listed in Table 5 to a single species remains questionable.

Figures

FIGURE 10. Porphyrocrinus cf. incrassatus. A – E: Walvis specimen (MNHN IE- 2012 - 760); A: general view; B: aboral cup (B: basal ring, C 1: proximalmost columnal, R: radial ring); C: detail of arm with muscular synarthry (m) and synostosis (s) Between brachial (Br) pairs; D – E: distal mesistele columnal of preserved stalk; F – G: Cape Basin stalk fragment (ZSM 20070046); F: proximal columnal (more distal position than D – E); G: distal columnal.