Ophiovalida Thuy, Eriksson & Numberger-Thuy 2024

Clade Ophiovalida clade nov. Diagnosis Ankhurid ophiuroids with the water vessel canal at least partially open and with lateral arm plates devoid of ambulacral groove spines. Etymology From ‘validus’, Latin for ‘valid, strong’, because the node in question represents the origin of the modern ophiuroid bauplan. Taxa included Muldaster haakei, Ophiurina lymani Stürtz, 1890 and all members of the clade Myophiuroidea. Remarks We introduce the new clade name Ophiovalida clade nov. to designate the key node in the evolution of ophiuroids marked by two major skeletal innovations, 1) partial opening of the water vessel canal and 2) the loss of ambulacral groove spines. The node in question is exceptionally well-studied in terms of stratigraphic dating, phylogenetic signal and paleoenvironmental context (Thuy et al. 2022). Specifically, it marks the transition between two temporally consecutive species, Ophiopetagno paicei and Muldaster haakei. Given its significance as the ‘moment of birth’ of the modern ophiuroids, we decided to name the clade bound to this specific node.