Brittle stars are among the most active and fastest moving echinoderms. They have the ability to show complex locomotory behaviors and use their flexible arms to produce a coordinated movement. Despite the interest in their movement, little is known about the intra- and interspecies variation in arm flexibility and movement. We performed a two-dimensional (2D) image processing on horizontal movement of three ophiuroid species (Ophiolepis superba, Ophiocoma scolopendrina, Macrophiothrix hirsuta), using two novel parameters, ‘sinuosity’ and ‘slip angle’, in a biological context to infer the ophiuroid movement and flexibility. The result illuminated the variability of individual arm use in the studied species. In addition, an investigation on relationship between morphological structure and its function showed that arm length and the extended keel in vertebrae can play a role in angle direction and flexibility of ophiuroid arms.

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