Description of three new species of Zenometridae (Echinodermata, Crinoidea, Comatulida), with new insights on species and genus delimitation

Zenometridae A.H. Clark, 1909 is a family of Comatulida that co-habits with corals or sponges in the deep-sea. It comprises five species attributed to three genera, characterized by a cavernous centrodorsal cavity, a complete basal circlet with a large central lumen, and a concave fulcral bowl of the cirrus sockets. This study reveals a high cryptic diversity of the family, with three new species (Sarametra varians sp. nov., Sarametra subtilis sp. nov., and Sarametra acuta sp. nov.), two undescribed species, and a novel clade from the Pacific Ocean. The new species demonstrate limited intra-specific COI genetic divergence (< 0.4%), yet showing a spectrum of morphological variations that used to be considered as intergeneric differences. A review of characters is carried out based on the new specimens and type specimens of the five known species. COI, 16S, and 28S genes are used for phylogenetic reconstruction, providing the first molecular phylogenetic tree of the family. Genera Psathyrometra and Sarametra are monophyletic with robust supports. A novel clade, Zenometridae gen. et sp. indet., is retrieved as sister to the Sarametra clade. The integration of molecular and morphological data has led to a revision of the generic diagnosis, offering a better understanding of the taxonomy and evolutionary relationships of the family.