Ammonicrinus jankei, Bohatý, 2011

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 : 630-631

Ammonicrinus jankei sp. nov.

Figs. 4B , 14B , 15C .

1952 Ammonicrinus wanneri Springer, 1926 ; Ubaghs 1952: 210, fig. 2, pl. 1: 1–7, pl. 2: 1–7.

1978 Ammonicrinus wanneri Springer, 1926 ; Ubaghs 1978: T78, fig. 57: 8.

pars 2003 Ammonicrinus wanneri Springer, 1926 ; Webster 2003: GSAwebpage, A. wanneri Springer, 1926 , Ubaghs 1952: 210, fig. 2, pl. 1: 1–7, pl. 2: 1–7 and Ubaghs 1978: T78, fig. 57: 8, only.

Etymology: After Eberhard Janke (Elsdorf), for his help in sampling of material, especially from time−consuming washings, for the present publication.

Type material: Holotype: SMF−XXIII.167a.

Type locality: Locality 8: Hill range near the “Steineberg”, N of Kerpen ,

S of Flesten within the Hillesheim Syncline (Eifel, Rhenish Massif,

Rhineland Palatinate, Germany).

Type horizon: “Rommersheim Formation” ( Ubaghs 1952: 206). My studies at the type locality suggest that the species came from the Freilingen Formation (upper Eifelian, Middle Devonian) .

Diagnosis.—An Ammonicrinus , distinguished by a crown with a rhombic outline, smooth cup ossicles and radiating ridges on radials, radials convex and protrude conically toward the lateral−exterior; arms formed by very wide, V−shaped and medium short brachials; mesistele distinguished by irregularly arranged columnals with longer and shorter LCEE, which are relatively wide, columnals of the mesistele interconnected with several columnals having broadened extensions that could interlock in a coiled position and are combined with smaller, “regular” columnals, mesistele sculptured by irregular tubercles (several tubercles could possibly be spine−tubercles but spines not preserved); shape of coiled stem, covering the crown, oblate spheroidal; cup nearly completely covered by the mesistele. Other skeletal elements unknown.

Ammonicrinus jankei sp. nov. is similar to A. sulcatus . The species differs in several characteristic morphologies: A. sulcatus has fine tubercles on the cup ossicles and the radials are convex and protrude conically toward the lateral−exterior. The cup ossicles of A. jankei sp. nov. are unpustulated but the radials have as many as six radiating ridges and each one has a slightly lobe−like enlarged appendage. The columnals of the mesistele of A. jankei sp. nov. are thinner in cross section than those of A. sulcatus and have irregularly arranged nodular tubercles instead of finer columnal sculpturing observed in A. sulcatus . The planispirally coiled, proximal column of A. sulcatus is relatively low, wide and barrel−shaped, due to the relatively short extensions of the columnals of the mesistele. In contrast, the shape of the coiled stem that covers the crown of A. jankei sp. nov. is oblate spheroidal.

Description.—The crown is mainly distinguished by its shape that shows a characteristic rhombic outline in lateral−anal view ( Fig. 4B 3 , B 4 ), which is caused by the radials, which are convex, conical, and extending toward the lateral−exterior. The cup is nearly completely covered by the mesistele. The ossicles of the cup are consistently unpustulated, with up to six radiating ridges on radials ( Figs. 4B 2 , 14B ). The lateral−most radials have a slightly lobe−like enlarged appendage that could possibly support the lateral water faecal−ejection ( Figs. 4B 2 , 14B ). The short arms are formed by very wide and V−shaped brachials, which are nearly straight in proximal position; the distal brachials are somewhat curved laterally. The species developed one single rhombic radianal plate obliquely at left below the C radial, followed by a larger anal X and several smaller anal plates forming a short and curved tube that presumably channelled the faecal material toward that point from where the excrements could be ejected toward the lateral−exterior. The short and narrow proxistele causes distinct impressions of columnals on the cup, proximal tube and subsequent arms ( Fig. 4B 4 ). The mesistele is sculptured by irregularly arranged tubercles and is distinguished by irregularly arranged columnals with longer and shorter extensions, showing regular columnals that are interconnected with several columnals with broadened LCEE that could interlock in coiled position. Several tubercles could possibly be badly preserved spine−tubercles (spines not preserved). Shape of the coiled stem that cover the crown is oblate spheroidal ( Fig. 4B 1 ). The connection between disti− and mesistele, the morphology of the dististele and of the holdfast are unknown.

For dimensions of the studied material, see indication of size within the figure descriptions.

Stratigraphic and geographic range.—(?)Junkerberg and Freilingen formations (Eifelian) to lower (?)Ahbach Formation (uppermost upper Eifelian) of the Hillesheim Syncline (Eifel, Rhenish Massif, Rhineland Palatinate, Germany). The species has its maximum distribution within the Freilingen Formation.

Figures

Fig. 4. First illustration of the actual plate diagram and definition of genus Ammonicrinus as a lecanocrinid Flexibilia by Ubaghs (1952). A. Ammonicrinus doliiformis Wolburg, 1938a (for 1937), SMF−XXIII−165a from the “Rommersheim Formation” of the Auburg, Gerolstein, Eifel, Germany (Ubaghs 1952: 220). View of coiled mesistele (A1); view of exposed proxistele (A2) (taken from Ubaghs 1952: pl. 3: 1, 3). B. Anomalous crown of “Ammonicrinus wanneri” from the “Rommersheim Formation” of the Steineberg, N of Kerpen, Eifel, Germany (Ubaghs 1952: 220) (= holotype of A. jankei sp. nov., no. SMF−XXIII−167a) coiled by the mesistele.View of the coiled mesistele (B1) (Ubaghs 1952: pl. 1: 3); partly excavated crown (B2), showing radiating ridges on radials and one slightly lobe−like enlarged appendage that possibly could support the lateral water respectively faecal−ejection (arrow) (Ubaghs 1952: pl. 1: 4); excavated crown in lateral view (B3, B4), the second “radianal plate” respectively “supplementary plate” (see arrows) is based on an anomaly (Ubaghs 1952: pl. 2: 3, 2); plate diagram (B5), showing the two anomalous plates (arrows) (slightly modified after Ubaghs 1952: 205, fig. 1); schematic drawing of the coiled specimen (B6); reconstruction of the assumed living feeding position (B7) (Ubaghs 1952: 110, fig. 2; p. 223, fig. 5). Not to scale.

Fig. 14. A. Schematic reconstruction of Ammonicrinus (strongly modified after Piotrowski 1977: 209, fig. 3) of a feeding Ammonicrinus within low−intensity current water. Alternating water pressure was possibly generated in the interior of the enrolled proximal stem by slow, bellow−like partial opening and closing (red arrows) of the base of the central mass; due to the synarthrial (bifacial) articulation of the ammonicrinid mesistele that developed two huge ligamentary facets (orange), separated by the fulcrum, bellow−like partial opening could possibly enabled by stiffening of the outer ligaments (see orange bars in A1); closing could be controlled by stiffening of the inner ligaments (see orange bars in A2). A1, suction during opening may result from low−pressure (P−) and create an ingesting water flow (blue arrow); A, ejection during closure (red arrow) resulted from overpressure (P+); to minimise faecal recycling, 2 the water ejection may have occurred laterally (blue arrows), feasibly at both lateral centres, which have “openings”. B. Lobe−like enlarged appendages (framed in red) could possibly support the lateral water faecal−ejection (modified from Ubaghs 1952: pl. 1: 4). C. Reconstruction of a feeding “encased runner−type” of A. leunisseni sp. nov., attached to a tabulate coral (model); the spined specimen dwelled enrolled on the muddy seafloor; alternating water pressure was obviously generated in the interior of the enrolled proximal stem globe by non−muscular, probably MCT−controlled, slow, bellow−like partial opening and closing of the oblate sphere at its bottom (dashed arrow); suction during opening created an ingesting water flow (see arrow on the left), which was funnelled in a “canal”, formed by the unspined interior of the columnals of the mesistele, whose U−shaped LCEE additionally formed a protection against immersive sediment; ejection during closure resulted from overpressure; to minimise faecal recycling, the water ejection occurred supposably laterally, feasibly at both lateral centres, which accordingly show “openings” (see arrows on the right). Not to scale.

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.

Fig. 3. The lecanocrinid species Ammonicrinus doliiformis Wolburg, 1938a (for 1937) from the Selscheid Formation of Ohle, Sauerland (Wolburg 1938a: 230). A. Casts of nearly complete specimen. Specimen attached to a brachiopod valve (right arrow) (A1), showing the characteristic triangular connection between mesi− and dististele (left arrow) and slightly compressed mesistele (from Wolburg 1938a: pl. 17: 1); detail view of the attachment disc (arrow) (A2), encrusting the brachiopod (from Wolburg 1938a: pl. 18: 8); detail view of the triangular connection between mesi− and dististele (arrow) (A3) (from Wolburg 1938a: pl. 17: 6a); detail view of the coiled, slightly compressed mesistele (A4) (from Wolburg 1938a: pl. 17: 4). B. Former assumed reconstruction of life mode, figured with a crown that protrudes toward the lateral−exterior (arrow) (from Wolburg 1938a: 240, fig. 5). C. Former assumed reconstruction of the crown (1938a: 233, fig. 4). Not to scale.

Fig. 2. The first figures of Ammonicrinus from Springer (1926) and Krause (1927). A. Ammonicrinus wanneri Springer, 1926 (from Springer 1926: pl. 6: 4a, b). A1, view of the extetrnal flanks of the coiled mesistele; A2, coiled mesistele in lateral view. B. Ammonicrinus leunisseni sp. nov. (= “A. wanneri” in Springer 1926: pl. 6: 5, 5b). B1, view of the extetrnal flanks of the coiled mesistele; B2, coiled mesistele in lateral view. C. Photograph of the holotype of Ammonicrinus wanneri Springer, 1926, USNM−S2115; lateral view of coiled mesistele; connection between mesi− and dististele, dististele and attachment missing (see fracture surface at distal mesistele). D. Photograph of USNM−S2115, the Springer (1926) original of “Ammonicrinus wanneri” (= A. leunisseni sp. nov. herein); lateral view of coiled mesistele; connection between mesi− and dististele, dististele and attachment missing (see fracture surface at distal mesistele). E. Ammonicrinus doliiformis Wolburg, 1938a (for 1937) (= “A. wanneri” in Krause 1927: pl. 8: 4, 2). E1, view of the extetrnal flanks of the coiled mesistele; E2, coiled mesistele in lateral view. A–D from the Middle Devonian, Eifel Limestone; Prüm, Eifel, Germany (Springer 1926: 25); E from the Middle Devonian of Sötenich, Eifel (Krause 1927: 456). A, B, E not to scale; C, D scale bars 10 mm.

Fig. 1. A. Reconstruction of the Ammonicrinus life time position (modified after Piotrowski 1977:208, fig. 2). B. Ammonicrinus plate diagram (not to scale).