Meeting Abstract
Snapping shrimp have specialized armor, termed the orbital hood, that covers their head and eyes. It has been proposed that orbital hoods protect the heads of snapping shrimp but impair their visual abilities. To explore the relationship between armor and vision in these animals, we examined the optical properties of the orbital hood, the morphology and physiology of the visual system, and the visually influenced behaviors of the big claw snapping shrimp Alpheus heterochaelis. We find that the orbital hoods of A. heterochaelis are made of transparent carapace that transmits 80-90% of incident light to their reflecting superposition eyes. Electroretinography (ERG) shows that the eyes of A. heterochaelis respond maximally to 500 nm light and demonstrate a flicker fusion frequency of > 40 Hz. Microspectrophotometry (MSP) reveals that the eyes of A. heterochaelis have two middle-wavelength sensitive (MWS) visual pigments that maximally absorb light at 501 and 519 nm. Behavioral trials using optomotor assays show that snapping shrimp demonstrate spatial vision with an angular resolution of ~ 8°. After discovering that A. heterochaelis has a functional visual system, we tested our hypothesis that the orbital hoods of snapping shrimp protect their heads from the shock waves produced by their snapping claws. To do so, we recorded shock waves produced by A. heterochaelis using pressure sensors mounted inside and outside of the orbital hoods of intact individuals. We compared these results to those from trials using individuals from which we removed orbital hoods. From these experiments, we discovered that orbital hoods decrease the magnitudes of shock waves by at least 40%. We conclude that the orbital hoods of snapping shrimp facilitate spatial vision and may protect their neural tissues from shock waves.
