Ammonicrinus kerdreoletensis Le Menn and Jaouen, 2003

Bohatý, Jan, 2011, Revision of the flexible crinoid genus Ammonicrinus and a new hypothesis on its life mode, Acta Palaeontologica Polonica 56 (3), pp. 615-639 : 627-628

Ammonicrinus kerdreoletensis Le Menn and Jaouen, 2003

Figs. 6, 11 , 15A .

2003 Ammonicrinus kerdreoletensis Le Menn and Jaouen, 2003: 207 , 210–211, fig. 4A–C.

Holotype: LPB−1073. The type locality is Coupe de Kerdréolet , niveau

K2, L'Hôpital−Camfrout, Département Finistère (Brittany, France); and the stratigraphy is Kerdréolet Formation, Emsian (Lower Devonian).

Material.— Type material and new material no. GIK−2121 ( Fig. 11 ).

doi:10.4202/app.2010.0020

Description.— Ammonicrinus kerdreoletensis has a subspherical crown with a relatively large cup in comparison to the narrow width of the mesistele; the cup is not covered laterally by the mesistele and is clearly visible in lateral view ( Fig. 11 ); the cup ossicles are unsculptured(?). The mesistele is very long and composed of numerous columnals (“exposed runner−type”) that have nearly uncurved to slightly concave external flanks and thin cross sections ( Fig. 11 ), LCEE of the mesistele regularly arranged and very short ( Fig. 15A ), several columnals of the mesistele have very short and blunt lateral expansions on both lateral edges of the exterior flanks; connection between mesi− and dististele obviously distinguished by a narrow triangular columnal, which follows distally after the rapid narrowing of the columnals of the distal−most mesistele; dististele and attachment unknown; shape of coiled stem narrow discoidal; mesi− and dististele obviously covered by echinoid spine−tubercles, which presumably bear articulated spines (not preserved).

Discussion.—The numerous columnals of the mesistele of Ammonicrinus kerdreoletensis , the very short lateral expansions of the mesistele and the huge rounded crown clearly separates this species from all other ammonicrinids.

As stated above, the cup of A. kerdreoletensis is laterally not covered by the LCEE. That possibly implies feeding in the current ( Fig. 6) and negates the internal, respectively pumping proposal assumed for the younger ammonicrinids described herein. Furthermore, the new recovered material indicates that the stem of A. kerdreoletensis tapers toward the crown, which was obviously elevated up from the substrate into a possible low velocity current for feeding. Therefore, A. kerdreoletensis can be designated a morphological progenitor of the younger and encased ammonicrinids.

Stratigraphic and geographic range.—Emsian (Kerdréolet Formation) of the Coupe de Kerdréolet, niveau K2, L'Hôpital−Camfrout, Département Finistère (Brittany, France) and lower Eifelian of Vireux−Molhain (southern Ardennes, northern France).

Figures

Fig. 11. The lecanocrinid species Ammonicrinus kerdreoletensis Le Menn and Jaouen, 2003 (GIK−2121) from Vireux−Molhain (locality 12, Appendix 1), France, lower Eifelian (Middle Devonian); lateral view of long mesistele, proxistele and huge cup (arrow) on matrix. Scale bar 10 mm.

Fig. 15. Schematic sketches of different LCEE of the mesistele in uncoiled (above) and coiled positions (below), indicating evolution of perfecting the crown−encasing in coiled position by modifying the extensions form Emsian to Givetian. A. Lateral view of Ammonicrinus kerdreoletensis Le Menn and Jaouen, 2003, showing similar shaped columnals with very short LCEE; thus, the crown is laterally nearly unprotected in coiled position.B. Lateral view of Ammonicrinus wanneri Springer, 1926, with lengthened LCEE of the similar shaped columnals, which lattice−like guarded the crown in coiled position. C. Lateral view of Ammonicrinus sulcatus Kongiel, 1958, showing smaller columnals of the mesistele, which are interconnected with longer ones and afford lateral density of the coiled stem. D. Lateral view of Ammonicrinus doliiformis Wolburg, 1938a (for 1937), showing regularly or irregularly arranged columnals with longer and shorter LCEE, which were interconnected with several columnals showing broadened convex and concave extensions that could interlock in coiled position.