Family HEMIEURYALIDAE Verrill, 1899

Type taxon. Hemieuryale von Martens, 1867 .

Diagnosis. Disc covered with thick plates with distinct centrodorsal and primary plates. Typically, one apical papilla flanked by a series of continuous lateral oral papillae. Bursal slits small, placed near margins of oral shields. Arms inserted laterally into the disc. Dorsal arm plates complete or replaced by a mosaic of small plates. Arm spines short and few. Spine articulation composed of two parallel ridges placed at an angle to each other (Verrill 1899a; Martynov 2010; Gondim et al. 2015).

Comments. Hemieuryalidae has been considered one of the least known families of Ophiuroidea, in regards to ecology, morphology, and phylogeny (Gondim et al. 2015). A recent study proposed moving Ophiochondrus and Ophiomoeris to Ophiacanthidae based on lateral arm plate morphology (Martynov 2010). Hemieuryalidae has peculiar ridges on its spine articulations, which are very different from other ophiuroids (Martynov 2010). The family has also been supported by a molecular phylogeny reconstruction using next-gen sequence-capture methodology (O’Hara et al. 2017). Hemieuryalids are associated with octocorals (Gondim et al. 2015) and hydrocorals (Hendler et al. 1995), but are also found as members of the epifauna (Borges, 2006). The family is comprised of 84 species distributed across ten genera (O’Hara et al. 2017). In Brazil, three species are recorded from three genera (Barboza & Borges 2012; Gondim et al. 2015).