Globulocrinus amphoraformis, Roux & Martinez & Vizcaïno, 2021

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 : 228-230

Globulocrinus amphoraformis n. gen., n. sp.

Figs. 14–15

Type material. 10 aboral cups from Réqui, illustrating the main morphological variations, including the holotype ( MNHN.F. A82011 ) ( Fig. 14G ) and 9 paratypes ( MNHN.F. A82012 ) .

Etymology. In reference to the aboral cup which usually is amphora shaped.

Material examined. In addition to the type series, 158 aboral cups from Réqui in the Martinez and Vizcaïno collections.

Diagnosis. Aboral cup covered by fine granulation with variable external morphology. In juveniles, aboral cup urn-shaped with neck formed by radial circlet, 1.0<Hc/Dc<1.7, usually strong constriction between basal and radial circlets, radials occasionally relatively high (Hr/Hc up to 0.44), radial circlet more or less flared, external face of each ossicle often very convex, conspicuous ossicle sutures, stalk insertion pentagonal. Juvenile characters fading or disappearing in largest specimens, with elongation of basals giving an amphora shape to aboral cups (as in holotype), Hc/Dc> 2 and reaching almost 3; relative height of radials (Hr/Hc<0.2) decreasing to 0.08 in largest specimens, radials substantially wider than high, stalk insertion becoming circular. Distal face of radial circlet with large central depression, pentagonal to slightly star-shaped. Brachials and columnals unknown.

Type stratum. Base of blue marls of the middle Ilerdian, above Solenomeris limestones, late NP10, but maybe already NP11.

Type locality. Réqui, north of Montlaur (commune de Val de Dagne, Aude) .

Description of type series. Quantitative characters of aboral cups of type series given in Table 14. Holotype illustrating the amphora shape of aboral cup with neck formed by radial circlet ( Fig. 14G ), intermediate between globular urn shape of juveniles ( Fig. 14A–E ) and oblong shape of larger specimens ( Fig. 14H–I ). Smallest paratype ( Fig. 14A ) with a flared radial circlet and a large adoral cavity, constriction at basal-radial transition well marked, maximum diameter at mid-height of basal circlet, very convex outer ossicle surfaces, very conspicuous sutures. All characters highly variable and may become less pronounced during growth: radials becoming markedly shorter than wide, radial circlet more or less flared ( Fig. 14A, E, G ), straight ( Fig. 14C–D, F, I ) or more or less conical ( Fig. 14B, H ) limiting diameter of adoral cavity; constriction between basal and radial circlets reduced ( Fig. 14C ), rarely disappearing ( Fig. 14H ); during growth, elongation of basals with disappearance of sutures and maximum diameter in adoral third ( Fig. 14F–I ); sutures between radials rarely disappearing ( Fig. 14H ), stalk insertion pentagonal in juveniles ( Fig. 14K–L ), becoming circular later. Adoral face of radial circlet most often incompletely preserved, fragile interradial crests, marked but not inducing any relief on outer edge of radial circlet; paratype 9 with worn or broken interradial crests, central pentagonal star-shaped depression with Dd/Dr about 0.4, muscular synarthries with narrow aboral ligament depression, deep subcircular muscular areas more or less equal in surface to internal ligament areas ( Fig. 14J ).

For all specimens, variation of main quantitative characters given in Table 15. About 90% of specimens with Dc <1.7 mm or Hc <3.6 mm, most with 1.2 <Hc/Dc <2.5, main ratios (Dr/Dc and Hc/Dc) uncorrelated leading to wide range of variation in aboral cup shape ( Fig. 15 ). Radial circlet flared 50%, straight 40%, conical 10%, Dr always much smaller than maximum diameter of basal circlet.

Remarks. Although highly variable, G. amphoraformis n. gen. n. sp. is easily recognised by its radial circlet that is well individualised with respect to the basal circlet. The shape of the larger aboral cups may converge with that of Pseudoconocrinus doncieuxi but their size remains much smaller. Compared to the ontogenic series of G. amphoraformis n. gen., n. sp., the single known specimen of the Bartonian species G. globulosus with its aboral cup as high as wide may suggest that it is a juvenile. However, its maximum diameter of 3.8 mm, much larger than that of the largest specimens of G. amphoraformis n. gen., n. sp. and its sutureless basal circlet surmounted by a radial circlet that is very close to that of the largest aboral cups from Réqui ( Fig. 14–I ), suggest rather an adult specimen. If this is the case, G. globulosus would be distinguished principally by the absence of basal circlet elongation during growth. Brachials are unknown. Columnals are unidentified.

Occurrence. Early Ypresian (middle Ilerdian) of Corbières; species only known from Réqui near Montlaur (Val de Dagne, Aude).

Figures

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.

FIGURE 15. Variation in main quantitative characters related to aboral cup shape of Globulocrinus amphoraformis n. gen., n. sp. from Réqui. Dc used as growth index. Values in mm, except for ratios Hc/Dc (green straight lines). See Fig. 2 for abbreviations.