Shock wave-damping orbital hoods cover the eyes of snapping shrimp (Alpheus heterochaelis) without impairing spatial vision.

Abstract

Snapping shrimp are protected from the shock waves they produce and use as weapons by a transparent, helmet-like extension of their carapace termed the orbital hood. Orbital hoods cover the eyes of snapping shrimp and may affect their vision by refracting light. Microcomputed tomography reconstructions of heads from Alpheus heterochaelis show orbital hoods are unlikely to influence vision because their focal lengths (33±7 mm) are almost 500× longer than their distance from the underlying eyes (71±9 μm). Optomotor behavioral trials support this prediction: visual acuity did not differ between animals with intact orbital hoods and those from which we had removed orbital hoods. We conclude that the orbital hoods of snapping shrimp neither impair spatial vision nor make meaningful contributions to it. The morphology and microstructure of orbital hoods may be constrained by requirements of the visual system, but orbital hood function is primarily protective rather than optical.