Pseudoconocrinus lavadensis, 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 : 220-225

Pseudoconocrinus lavadensis n. sp.

Figs. 10–13

Type material. The type series, deposited in the collections of the Muséum national d’Histoire naturelle de Paris (see Table 1), comprises a selection of 15 aboral cups, 7 of which are figured ( Fig. 10 ), including the holotype ( Fig. 10A–B ), 7 brachials including 2 figured ( Fig. 11A–C ), 35 columnals of the proxistele, including 4 figured ( Fig. 11D–G ), 40 columnals of the mesistele and more distal ones, including 3 figured ( Fig. 11H–L ) and 10 fragments of rhizoids including 3 figured ( Fig. 11M–O ).

Etymology. From Lavade near Fontcouverte (Aude), where the type series and abundant material were collected.

Material examined. Numerous ossicles in sieving residues (20 kg of sediment) from Lavade (113 aboral cups, 3,656 columnals, numerous brachials), and 3 aboral cups and 29 columnals from La Côte (Moux). Those that were not selected to constitute the type series, are in the Martinez Collection .

Diagnosis. Aboral cup often subspherical, more or less flattened both aborally and adorally, with distal face displaying a low to moderate relief, central star-shaped depression equal to or less than one third of distal diameter of radial circlet, ratio Dc/Hc between 0.64 and 1.33 (mean 0.88), ratio of diameter of stalk insertion to Dc most often between 0.30 and 0.50. IBr1 1.5 times wider than high, distal facet convex. IBr2ax pentagonal; proximal facet very concave with neural canal lumen subrectangular, distal muscular synarthries lateral edges juxtaposed to form very marked medial crest. IIBrax unknown; numerous brachial pairs. Well-differentiated proxistele; proximalmost discoid columnals with flat facets, becoming thicker distally with concave facets devoid of a fulcral ridge and maximum diameter at mid-height. Proximal mesistele columnals with external surface usually strongly convex and almost as high as wide (H/D <1.5); distal columnals displaying the same general shape and lateral convexity often only marked at mid-height or fading; 2 to 4 rhizoid sockets per columnal, occasionally 5.

Type stratum. Middle blue marls of middle Ilerdian age, upper NP11.

Type locality. Lavade near Fontcouverte (Aude).

Description of aboral cups of type series. Holotype (MNHN. A82001 ) ( Fig. 10A–B ) subspherical, slightly flattened along adoral-aboral axis (HC/Dc 0.81), smooth external surface, indistinct sutures; aboral diameter (stalk insertion) 1/3 Dc; distal face of radial circlet wide (Dr/Dc 0.90) and low relief with moderately developed central star-shaped cavity (Dr/Dc 0.26), discrete rectilinear interradial ridges and articular facets mainly occupied by ligament areas. Quantitative characters of the 15 aboral cups of type series given in Table 7. General shape varying from slightly pyriform ( Fig. 10C, G ) to strongly flattened ( Fig. 10I ), stalk insertion deeply concave with edges usually well-marked ( Fig. 10E ); relief of the distal face of radial circlet highly variable, occasionally almost flat ( Fig. 10I ) or with interradial ridges ending in strong widening at edge of central cavity forming more pronounced relief ( Fig. 10F, J ); central cavity circular ( Fig. 10F ), pentagonal ( Fig. 10J ), occasionally star shaped as in the holotype, most often Dd/Dr<0.35; sutures between basals always indistinct except sometimes towards aboral end. Paratype 11 with three IBr1 still attached to aboral cup ( Fig. 10K–L ). Paratype 8 with one radial recessed, smaller than others, but witout trace of predatory attack.

Description of brachials, columnals and rhizoids of type series. Quantitative characters of primibrachials of type series given in Table 8. Three IBr1 still attached to paratype 11 ( Fig. 10K–L ), two of them slightly dissociated from adjacent radials, convex and spindle-shaped outer surface, almost 1.5 times wider than high, very convex distal outer border, distal facet convex but poorly preserved. Thick, subpentagonal IBr2ax with rectilinear or slightly concave distal outer edges ( Fig. 11A ), proximal facet strongly concave with subrectangular neural canal ( Fig. 11B ), broad adoral axial gutter ( Fig. 11C ).

Quantitative characters of the columnals of the proxistele given in Table 9. Most proximal columnals cylindrical and flat faced, occasionally with slightly raised perilumen ( Fig. 11D–E ), most frequent proximal columnals from a more distal position in the proxistele with higher values of H and displaying concave facets without a fulcral ridge and external surface usually markedly convex ( Fig. 11F ), proxistele-mesistele transition identified by appearance of rudimentary fulcral ridge ( Fig. 11G ) and H/D values reaching 1. Columnals articulated by synarthries showing lateral bulge at mid-height ( Fig. 11I ) or not ( Fig. 11H ); 8-shaped ligament fossa well developed without extension on either side of fulcral ridge, fulcral ridge with regular secondary crenulation and more or less marked axial groove ( Fig. 11J–K ). Distal columnals with rhizoid socket diameter <0.6 mm ( Fig. 11H–L ). Rhizoid segments up to 7.5 mm long with diameter between 0.41 and 1.42 mm, ossicles of highly variable height (0.7<H<7.7), largest unbranched H 4.5 mm and D 1.3 mm, fragments of proximal rhizoids with clear articular sutures (synostoses) and often with large branch at one end ( Fig. 11M–N ), more distal fragments with fused ossicles and multiple sockets of small rhizoids ( Fig. 11–O ).

Description of other ossicles. Variations of aboral cups collected at Lavade summarised in Table 10; general shape variations moderate (0.7<Hc/Dc<1.33) within a group composed of some of the largest specimens, and relatively restricted in others (0.7<Hc/Dc<1.0) ( Fig. 12 ). IBr1 very rarely found; one isolated IBr in Martinez Collection showing proximal facet with protruding fulcral ridge and large, deep muscular areas. IIBr2ax unknown, despite abundance of material collected. Other brachials with characters similar to those of P. doncieuxi . Washing of 20 kg of sediment provided 35 columnals of circular facets belonging to proxistele (0.96%) and 3,621 columnals articulated by oval synarthries of which 2,385 (65.23%) bearing one or more rhizoid sockets. Measurements were made on a randomly selected sample out of 263 columnals articulated by synarthry ( Table 11; Fig. 13 ) with usually 0.85<H/D<1.45, H/D remaining highly variable during growth, quantitative characters alone not allowing to distinguish columnals from mesistele and dististele; frequent lateral bulging at mid-height (48% with d’/d> 1). 20, 28 % with d /D> 1.0); 70 % of synarthries with 1.15 <D/d <1.50; distal pluricolumnals from 2 to 5 columnals, rhizoid insertions per columnal in variable number (35% 1 insertion on 1 facet, 50% 2 insertions on 1 facet, others>2 insertions up to 5), maximum diameter 1.25 mm for columnal with D 2.9 mm and d 2.15 mm.

Remarks. Sediment samples from Lavade have yielded 33 columnals (excluding proxistele) per aboral cup, 65% of which bear rhizoid sockets. This suggests a much shorter stalk (mean 92 mm) in P. lavadensis n. sp. than in P. doncieuxi (mean 165 mm). In P. lavadensis n. sp. the relatively high frequency of columnals from the proxistele indicates a more developed and well-differentiated proxistele composed of columnals with markedly concave facets and devoid of a fulcral ridge; these features are unknown in P. doncieuxi . The subspherical shape of aboral cups in P. lavadensis n. sp. corresponds to an increase in height delayed in favour of an increase in diameter during the ontogeny of the basal circlet ( Fig. 12 ), which is the contrary of what is observed in P. doncieuxi ( Fig. 5 ). The two species of Pseudoconocrinus from Corbières clearly differ in the opposite ontogenic trajectory of their aboral cup ( Fig. 9 ). Table 12 summarises the main characters that distinguish P.lavadensis n. sp. from P. doncieuxi .

Occurrence. Early Ypresian (middle Ilerdian, upper NP 11) in Corbières, only known from Lavade (Fontcouverte) and La Côte (Moux).

Figures

FIGURE 5. Variations in the shape of columnals and aboral cups of Pseudoconocrinus doncieuxi (sites near Fontcouverte, with the exception of Lavade). The colour envelopes cover more than 90% of specimens; black lines indicate the values of H/D (left) and Hc/Dc (right). Values in mm, except for ratios (black straight lines). See Fig. 2 for abbreviations.

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 10. Aboral cups of the type series of Pseudoconocrinus lavadensis n. sp. from Lavade (Fontcouverte), documenting intraspecific morphological variations. A–B: holotype (MNHN.F.A82001); C–L: paratypes (MNHN.F.A82002), C: paratype 2, D–F: paratype 5, G–H: Paratype 6, I: Paratype 7, J: Paratype 4, K–L: Paratype 11;A, C, D, F, H–J: distal oblique views; B: distal face of radial circlet; E: oblique view of aboral face with stalk insertion; G, K–L: lateral views; K–L: specimen preserved with three IBr1, two of which in process of dissociation (K) and one remaining in place (L). Scale bar equals 1 mm.

FIGURE 11. Brachials, columnals and rhizoids of the type series of Pseudoconocrinus lavadensis n. sp. from Lavade. A–C: IBr2ax (MNHN.F.A82004), A: oblique external view, B: same specimen, detail of proximal synostosis, C: other IBrax, inner view; D–G: proxistele columnals (MNHN.F.A82006); F–G: proxistele-mesistele transition; H–L: distal stalk columnals and rhizoid fragments (MNHN.F.A82008), H: columnals without swollen body, I–L: columnals with swollen body, K: detail of fulcral ridge of J; M–O: rhizoid fragments. Scale bar equals 1 mm, except for K where it equals 0.5 mm.

FIGURE 12. Variations in main quantitative characters related to aboral cup shape of Pseudoconocrinus lavadensis n. sp. from Lavade. Values in mm, except for ratios HC/DC (green straight lines). See Fig. 2 for abbreviations.

FIGURE 13. Variation in main quantitative characters of columnals from Lavade. Other species: columnals that can be attributed to?Democrinus elongatus. To make the scatter plot clearer, only ~50% of columnals bearing rhizoids were represented. Envelopes encompass at least 90% of all groups of columnals. D and d used as growth index. Values in mm, except for ratios H/D (black straight lines at left). See Fig. 2 for abbreviations.