Classification of Isocrinida (Echinodermata: Crinoidea) with the description of a new extant genus and species from the western Pacific

Abstract

Abstract Previous molecular phylogenetic reconstructions have highlighted frequent convergences and iterations of external morphological characters during the evolution of crinoids. Classifications of extant and fossil crinoids based on these characters need to be thoroughly revised. This is particularly the case for the Isocrinida. We propose a new classification of this order based on molecular data and ontogenetic analysis of the derived characters displayed on ossicles and their articulations. The argument is strengthened by the discovery and description of a species belonging to a new genus (Panglaocrinus isseliformis gen. nov., sp. nov.) closely related to the genus Isselicrinus, which was abundant and widespread during the Late Cretaceous and Eocene. Extant Isocrinida appear to be divided into two major lineages that we interpret as two distinct families: Isocrinidae and Balanocrinidae. Isocrinidae are represented by the subfamily Metacrininae (genera Metacrinus and Saracrinus), while Balanocrinidae comprise four subfamilies: Balanocrininae (Neocrinus), Diplocrininae (Endoxocrinus and Teliocrinus), Isselicrininae (Panglaocrinus), and Proisocrininae (Proisocrinus). In the absence of molecular data, the genus Cenocrinus has not been attributed to any subfamily, but its close relationship to Balanocrinidae is suggested. Possible relationships between Mesozoic and modern taxa are discussed, although descriptions of arms in the palaeontological record are often important details.