Rhizocrinidae Jaekel, 1894

Roux, Michel, Martinez, Alain & Vizcaïno, Daniel, 2021, A diverse crinoid fauna (Echinodermata, Crinoidea) from the Lower Eocene of the Gulf of Languedoc (Corbières, Aude, southern France), Zootaxa 4963 (2), pp. 201-242 : 211-212

Family Rhizocrinidae Jaekel, 1894

Remarks. The distal face of the radial circlet ( Fig. 2B ) and the presence or absence of axillary brachials ( Fig. 2D ) have been shown to be highly useful for distinguishing the various rhizocrinid genera ( Roux et al. 2019). Those authors subdivided Conocrinus (sensu lato) into three genera, namely Conocrinus (sensu stricto), Paraconocrinus and Pseudoconocrinus . Although appearing as early as the Ypresian, Conocrinus (sensu stricto) was not found in Ilerdian strata of Corbières. The proximal columnals that constitute the proxistele of rhizocrinids are more or less thick and disc shaped, usually with flat and smooth facets. They are rare or absent in the screen-washed residues that we picked by hand. The columnals of the mesistele and dististele have synarthrial articulations with a central ligamentary fossa that has a figure-8 shape. The fulcral ridges change orientation from one joint to the next, giving the columnals a twisted appearance ( Fig. 2E–F ). Most rhizocrinids are fixed by rhizoids developed from the distal part of the stalk (dististele). In the fauna described here, the columnal characters do not allow a clear distinction between the different genera. The external morphology of juvenile aboral cups occasionally shows clear, discriminating characters, which tend to disappear later during growth by morphological convergence (homoplasy; for example, see Fig. 14A–I ). The abundance of material from some outcrops has allowed the recognition of juveniles and the reconstitution of ontogenic trajectories that have proved instrumental in clarifying the taxonomy (see Fig. 9 , for example).

Stratigraphical distribution. Campanian-Recent.

Figures

FIGURE 2. Characters and main parameters of aboral cups, brachials and columnals in Rhizocrinidae and the centrodorsal of Amphorometra. A–B: aboral cup, A: lateral view (b: basal, r: radial, Dc: maximum diameter, Dp: diameter of stalk insertion = proximalmost stalk diameter, Dr: diameter of distal radial circlet, Hc: height), B: distal face of radial circlet [Dc: maximum diameter, Dd: diameter of central cavity,, fr: fulcral ridge, ic: interradial crest, il: inner (adoral) ligament, m: muscular insertion, nc: neural canal, ol: outer (aboral) ligament, Wr: width of radial]; C: muscular synarthrial facet of non-axillary brachial (W: maximum width parallel to fulcral ridge, other abbreviations as in B); D: external face of axillary brachial (H: height, Wd: distal width, Wm: width of articulation with IIBr1, Wp: proximal width); E–F: distal columnal (f: 8-shaped ligament fossa, fr: fulcral ridge, D: largest facet diameter, d: smallest facet diameter, d’: mid-height diameter, H: height, rs: rhizoid socket), E: view from articular facet, F: lateral view; G–H: Amphorometra centrodorsal (a: aboral apex, cs: cirrus socket, D: maximum diameter, D’: diameter of central cavity, Dcs: diameter of largest cirrus socket, ib: insertion of basal, ir: interradial ridge), G: adoral view, H: lateral view.

FIGURE 9. Variations in main quantitative characters related to columnal shape and aboral cups of P. doncieuxi suboblongus n. subsp. from Réqui. The coloured envelopes cover more than 90% of specimens; straight lines indicate values of H/D (left) and Hc/Dc (right) (in purple: specimens from Réqui, and, for comparison, in green: P. doncieuxi from the Fontcouverte sites, except for Lavade, in red: P. lavadensis n. sp. from Lavade). Dp and red bar: range of stalk insertion diameter (= proximalmost stalk diameter) measured on aboral cups from Réqui. Values in mm, except for ratios (black straight lines). See Fig. 2 for abbreviations.

FIGURE 14. Aboral cups of type series of Globulocrinus amphoraformis n. gen., n. sp. from Réqui. A–I: lateral views showing variations and changes in morphology during ontogeny, G: holotype (MNHN.F.A82011); A–F, H–L: paratypes (MNHN. F.A82012), A: paratype 1, B: paratype 2, C and K–L: paratype 3, D: paratype 4, E: paratype 5, F: paratype 6, H: paratype 7, I: paratype 8, J: distal face of radial circlet of paratype 9; K–L: aboral views of basal circlet of paratype 3, showing pentagonal depression corresponding to stalk insertion. Scale bar equals 0.5 mm.