Original paper
First record of cystidean and determinable pentacrinoid stages in fossil Crinoidea ‒ with new insights into the oral and anal endoskeletal anatomy of the Devonian subfamily Cupressocrininae (Eucladida)
Bohatý, Jan; Ausich, William I.
Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen (2025)
94 references
published online: Aug 8, 2025
manuscript accepted: Jul 2, 2025
manuscript received: Jun 16, 2025
DOI: 10.1127/njgpa/1274
Abstract
Cystidean and pentacrinoid stages of the Paleozoic crinoid subfamily Cupressocrininae (Eucladida) are presented for the first time from the Middle Devonian (middle Eifelian to middle Givetian) carbonate deposits of the Bergisch Gladbach-Paffrath Syncline (Bergisches Land, North Rhine-Westphalia) and the Eifel Synclines (Rhineland-Palatinate) of the Rhenish Slate Massif (Germany). This is the first evidence of a crinoid cystidean stage in the fossil record – as well as the first determinable pentacrinoid stages. Data for this study are based on specimens of various genera and species in the Cupressocrininae, and recent revisions to generic and species concepts within the Cupressocrininae are summarized. Specimens examined include calcareous preserved aboral cups, larval aboral cups with preserved primary peristomial cover plates (PPCPs), and crowns. In the course of ontogeny, six stages (1–6) can be distinguished from the post-doliolarian sessile cystidean and the pentacrinoid to the adult stage: (1) Late cystidean stage of the aboral cup ossicles has a fused infrabasal circlet, a stem facet with three or four peripheral columnar axial canals surrounding the central canal, five basal plates, and five semi-elliptical PPCPs positioned above these interradially. (2) In the early pentacrinoid stage, the radials are inserted into the aboral cup in a radial position on the upper corners of the basal plates. Above these radials, which are not yet in lateral contact with each other, the proximal primibrachials 1–2 are inserted between the PPCPs and the basals. (3) Middle pentacrinoid stage is characterized by the resorption or rejection of the PPCPs and lateral contact closure of radials and primibrachials 1–2, which have developed visible pinnules. The consolidating apparatus and the tubular anal sac in its CD-interradius is formed. (4) Late pentacrinoid stage is characterized by the development of the mono- or multilamellar exoplacoid layer and of its specific sculpturing. In addition, the radial plates gain increasing height. (5) Development of additional pinnule-bearing primibrachials and the further differentiation of the mono- or multilamellar exoplacoid layer and its specific sculpturing characterizes the young adult stage. This stage is also marked by the differentiation of species with clearly wider than long primibrachials and species with a clearly reduced infrabasal circlet. (6) The final development of the characteristic genus- and species-specific endoskeletal features of adults, includes a species with only two pinnule-bearing primibrachials. The previous assumption that the endoskeletal “consolidating apparatus”, characterizing the oral regions of the aboral cups in family Cupressocrinitidae, consists of five highly modified, unfused oral plates has been refuted. Development of the consolidating apparatus, which is primarily responsible for the muscular connection between the aboral cup and the first pinnule-bearing primibrachials, as well as for the positioning of the anal opening, is instead most likely linked to the development of the radial plates and is termed the “brachial muscular attachment elements”. All ossicles of the apparatus are newly described. Further findings on the homology of the endoskeletal anal structures of Cupressocrininae and Rhopalocrininae support and extend previous knowledge: both have a higher anal sac comprised of polygonal endoskeletal ossicles, which extends distally within the arms between the CD interray and the center of the consolidating apparatus.
Keywords
Devonian • Crinoidea • Eucladida • Cupressocrinitidae • ontogeny • cystidean stage • pentacrinoid stage