Molecular phylogeny based on increased number of species and genes revealed more robust family-level systematics of the order Euryalida (Echinodermata: Ophiuroidea).

Previous molecular analysis of the order Euryalida (Echinodermata: Ophiuroidea), has identified three monophyletic families, the Euryalidae, Asteronychidae and Gorgonocephalidae. However, family-level relationships have remained unresolved due to inadequate taxon sampling and insufficient molecular markers. Here, we present a family-level revision of the Euryalida based on sequences from mitochondrial genes (16S rRNA and COI) and a nuclear gene (18S rRNA) from 83 euryalid ophiuroids. The monophyly of the three families, Euryalidae, Asteronychidae and Gorgonocephalidae is confirmed. The Euryalidae and Asteronychidae+Gorgonocephalidae are assigned to superfamilies, the Euryalidea and the Gorgonocephalidea, respectively. Three subclades within the family Gorgonocephalidae are identified and assigned to three subfamilies; Astrotominae includes Astrocrius, Astrohamma and Astrotoma, Astrothamninae (subfamily nov.) includes Astrothamnus and Astrothrombus with Gorgonocephalinae including the remaining genera. Morphological characters are consistent with the newly recognised superfamilies and subfamilies.