Peculiar and Novel Morphologies in Paleozoic Brittle Stars (Echinodermata, Ophiuroidea) from the Lower Devonian Hunsrück Slate of Germany

The ophiuroid fauna preserved in the Hunsrück Slate is the most diverse known from the fossil record. Recognized here are 16 species and 14 genera. Although preservation in the Hunsrück can be exceptional, the preparation methods available to the last systematic treatment of Lehmann (1957) were mechanically challenging and very time-consuming, limiting the number of specimens available for study. Improvement in airbrasive technology and fine-tuning of preparation techniques, primarily by German fossil collectors, provided the basis for the detailed study and redescription of Hunsrück Slate ophiuroids discussed here. Several unusual skeletal morphologies, some previously unknown in Paleozoic ophiuroids, could be identified or described in detail for the first time.

The cheiropterasterids Cheiropteraster giganteus and two species of Loriolaster exhibit an atypical skin membrane that covers the entire interradius between arm tips. Recognized here are unusual dorsal extensions of the lateral ossicles that appear to act as membrane supports near the disk margin in both taxa. Cheiropteraster giganteus also has peculiar ambulacrals that exhibit broad, pore-like openings that extend from the ventral to the dorsal surface. The laterals of Loriolaster are laterally elongated and ventrally flattened instead of providing support to and protection of the podial basins. The rare, multi-armed furcasterid Kentrospondylus decadactylus bears novel, V-shaped, prong-like articulations on its ambulacrals, features that are lacking in the otherwise very similar Eospondylus primigenius. New among known furcasterid morphologies, Lapworthura lehmanni has arms covered dorsally by spine-bearing scales. The ophiurinid Ophiurina lymani bears small diamond-shaped dorsal arm ossicles but lacks their ventral counterparts.

Soft-tissue preservation is recognized in at least four species of Hunsrück ophiuroids. Previously, pyrite textures of the disk membrane of Loriolaster were shown to be consistent with soft-tissue preservation. However, the latter form of morphological preservation must be carefully separated from artificial pyrite structures that are presented here.