Calycocrinidae Moore and Strimple, 1973

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 : 622-623

Family Calycocrinidae Moore and Strimple, 1973 Genus Ammonicrinus Springer, 1926

Type species: Ammonicrinus wanneri Springer, 1926 .

Description.—The crown is short, rounded asymmetrically and incurved strongly in plane bisecting AE and CD interrays; the cup is either laterally uncovered by the mesistele ( A. kerdreoletensis ), partly visible in lateral respectively radial view ( A. doliiformis ), or completely covered by the mesistele (e.g., A. leunisseni sp. nov.); infrabasals reduced to 2 subequal, symmetrically disposed plates, which are larger than any of the three basals adjoining them on posterior side ( AB and EA basals lacking); A and E radials symmetrically disposed and distinctly larger than others, with margins of articular facets rather strongly curved; one single and rhombic radianal plate obliquely at left below C radial. The plates are either unsculptured (? A. kerdreoletensis ), sculptured with fine tubercles ( A. doliiformis , A. leunisseni sp. nov., A. sulcatus , A. wanneri ) or with radiating ridges on radials ( A. jankei sp. nov.). A large anal X is positioned above CD basal and followed by several smaller plates of the anal tube. The arms are formed by wide, short and straight or laterally somewhat curved brachials, branching isotomously on primibrachials 5 to 8 with up to 10 secundibrachials in some branches, followed by 10–20 tertibrachials. The stem is distinguished by the abrupt xenomorphic change between the dististele, which is composed of more or less elongated and cylindrical to barrel−shaped columnals; the mesistele, composed of columnals with herein termed lateral columnal enclosure extensions ( LCEE) covering the crown, and the proxistele with smaller lateral extensions on columnals; the dististele is either long and composed of numerous columnals (“exposed runner−type”, observed in A. kerdreoletensis ; “encased runner−type”, observed in all ammonicrinids, except of A. kredreoletensis ), short and composed of only few columnals, or reduced (“settler−type”, recognised in A. leunisseni sp. nov., A. sulcatus and A. wanneri ); the dististele can develop radices (rare, observed in A. leunisseni sp. nov.) and the distal−most dististele is connected with a substrate−controlled holdfast, in form of an attachment disc or a variously formed holdfast composed of radices; the LCEE of the mesistele are either constantly equally developed ( A. kerdreoletensis , A. wanneri ), composed of regularly or irregularly arranged columnals with longer and shorter extensions ( A. jankei sp. nov., A. sulcatus ), or interconnected with several columnals with broadened LCEE that could interlock in coiled position and are combined with smaller, “regular” columnals ( A. doliiformis , A. leunisseni sp. nov.); the connection between dististele and mesistele is either constant, by the development of a triangular columnal ( A. doliiformis ) or variously formed with floating transitions between those individuals with none or one to several columnals with LCEE on the proximal−most, barrel−like dististele and the following mesistele, which is solely distinguished by LCEE (observed in A. leunisseni sp. nov., A. sulcatus and A. wanneri ); the proxistele causes distinct impressions of columnals on cup. The axial canal is rarely tetralobate but typically pentalobate, with either five similar lumen angles or one lumen angle elongated (differences observed in one specimen). Ammonicrinus shows synarthrial articulation, with fulcra aligned and unequal ligmentary areas on either side of each fulcrum which produced the planispirally coiled proximal column covering the crown; shape of coiled stem narrow discoidal ( A. wanneri ), oblate spheroidal ( A. leunisseni sp. nov., A. jankei sp. nov.), or wide barrel−shaped ( A. doliiformis , A. sulcatus ). Mesi− and dististele are covered by echinoid−like tubercles, which bear articulated spines (recognised in A. doliiformis , A. leunisseni sp. nov., A. sulcatus and assumed in A. kerdreoletensis , A. jankei sp. nov.), mesistele sculptured by irregularly placed tubercles and additional spine−tubercles ( A. sulcatus ) or irregularly arranged ridges without tubercles on the exterior flanks ( A. wanneri ).

Stratigraphic and geographic range.—Devonian. Pragian (Lower Devonian) of the Czech Republic (see Hotchkiss et al. 1999: 331, fig. 2.21; Prokop 2009); upper Emsian (Lower Devonian) of the Armorican Massif ( France); lower Eifelian (Middle Devonian) of Vireux−Molhain, southern Ardennes ( France); lower Eifelian to Lower (?Middle) Givetian (Middle Devonian) of the Holy Cross Mountains ( Poland), the Rhenish Massif (Eifel, Sauerland and Bergisches Land, Germany), Cantabrian Mountains ( Spain) and Morocco (Harald Prescher, personal communication 2008; material not figured herein).

Because “ Ammonicrinus ? nordicus ” sensu Yakovlev and Ivanov (1956), from the Carboniferous of the Donetz Basin ( Russia), is herein excluded from Ammonicrinus sensu Springer (1926) , the genus is restricted to the Lower and Middle Devonian (Pragian–Givetian).