The retinas of mantis shrimps from low-light environments (Crustacea; Stomatopoda; Gonodactylidae)

1.	We examined microspectrophotometrically the retinas of 3 species of stomatopods in the superfamily Gonodactyloidea, all of which live in environments that are reduced both in the intensity and spectral range of natural illumination. Species examined were Odontodactylus brevirostris, O. scyllarus, and Hemisquilla ensigera.
2.	All 3 species had the typical gonodactyloid diversity of visual pigments, with 8 different photopigments residing in the 4 tiered rows of the midband and 2 additional types in the untiered classes of photoreceptors in the midband and peripheral retina. The spectral range covered by the max values of the visual pigments of each species was similar to that of other gonodactyloid and lysiosquilloid species.
3.	Apparent retinal adaptations in species of Odontodactylus for vision in dimly lit, spectrally narrow photic environments were seen primarily as specializations of the intrarhabdomal filters. These were of reduced diversity, and had reduced absorption at long wavelengths compared to the filters of other gonodactyloid stomatopods. Retinas of H. ensigera lacked both proximal classes of intrarhabdomal filter, and had the smallest total range of visual pigment max yet observed in mantis shrimps. These modifications decrease the spectral range and number of types of narrow-band spectral classes of phooreceptors, while increasing their sensitivity.