On <i>Ophioderma</i> (Echinodermata: Ophiuroidea) coming of age: morphological variations in three eastern Pacific species

Abstract Brittle stars undergo remarkable morphological changes during their transition to adulthood, extending beyond metamorphosis. Members of the genus Ophioderma exhibit particularly noteworthy morphological changes between the juvenile and adult stages. These growth changes have been a persistent source of misidentification in Ophioderma , even leading to the misclassification of juveniles to a different genus. In this study, the growth changes of three common eastern Pacific Ophioderma species were characterised: Ophioderma aija, Ophioderma occultum , and Ophioderma panamense . Their growth series, ranging from 2.5 to 26.7 mm disc diameter, were analysed by combining morphology, morphometrics, and DNA barcoding. Three size groups within the species were identified. In general, the morphological changes shown by the three species were highly similar and occurred at comparable sizes, allowing a pattern to be identified and reconstructed. However, differences between the species were observed throughout the series in quantitative (arm length, dorsal arm plates, number of arm spines) and qualitative (radial shields, colouration) characters. This work represents one of the few available contributions on the growth changes of Ophiuroidea from the eastern Pacific and so far in the genus Ophioderma .