Life, as we know it on Earth, is dependent on solar electromagnetic radiations. Since life appeared on this planet, light has indeed been one of the most important selective evolutionary forces for living organisms. Most of the organisms respond in some way to light, moving, orienting, flying, or swimming towards or away from it. Despite their absence of eye sensus stricto, echinoderms are no exception to the rule. Numerous echinoderm species are indeed light sensitive and sea urchins and brittle stars exhibit a large opsin gene diversity. Opsin light receptors are defined as the primordial actors of visual-like photoreception. Based on multiple transcriptome analyses, we present new findings in echinoderm opsin diversity. The specific case of two ecologically distinct brittle stars is approached including behavioural and molecular results. Even Amphiura filiformis do not exhibit escape behaviour upon light; light is known to control its feeding activity. Ophiopsila aranea exhibits clear escape behaviour upon light of various wavelengths. A comparative view of opsin gene expression is envisaged. Rhabdomeric opsin is proposed to be involved in the visual-like process of O. aranea. Even opsin can be considered as the basis of the light perception, skeleton structures are suspected to be important for the emergence of visual-like behaviour in echinoderms.
Delroisse, J., Ullrich-Lüter, E., Valero-Gracia, A., D’Agniello, S., Arnone, M.-I., Mallefet, J., & Flammang, P. (2014). Molecular basis of the echinoderm vision. In Royal Belgian Zoological Society (RBZS) (ed.), ZOOLOGY 2014 (p. p. 142). https://hdl.handle.net/2078.5/39261