A tale of two genera: new species and phylogenetic insights into deep-sea brittle stars Asteroschema and Ophiocreas (Ophiuroidea: Euryalidae)

Abstract Asteroschema and Ophiocreas are two diverse genera within the family Euryalidae, playing important ecological roles in deep-sea environments and contributing to the resilience of vulnerable ecosystems. However, the phylogenetic relationship between the two genera remains unclear owing to ambiguous diagnostic characters. In this study, 176 specimens, representing 24 species from both genera, were examined morphologically. Four genes (COI, 16S, 18S, and 28S) were sequenced for molecular species delimitation and phylogenetic reconstruction. The systematic issues were clarified, and a new classification was proposed, transferring 15 species from Asteroschema to Ophiocreas. The presence or absence of coloured bands or patches on the arms and disc was identified as the key character distinguishing the two genera. Additionally, three new species, Asteroschema maculatum sp. nov., Ophiocreas nudusorale sp. nov., and Ophiocreas jiaolongi sp. nov., were described based on morphological differences in the shape and arrangement of epidermal ossicles, the colour of bands and patches, and the shape of the lateral arm plates, supported by phylogenetic analysis. Our research also revealed that both genera are found primarily in the western tropical Atlantic and the Indo-Pacific regions, highlighting these areas as significant hotspots of marine biodiversity.