Multiple spectral classes of photoreceptors in the retinas of gonodactyloid stomatopod crustaceans

Abstract

1. We examined the compound eyes of 2 species of gonodactyloid stomatopods, Gonodactylus oerstedii and Pseudosquilla ciliata, using end-on microspectrophotometry of frozen sections of dark-adapted retinas. 2. The cornea and crystalline cones of both species were virtually transparent from 350 to 700 nm. Primary screening pigment granules in the retinular cells had the broad absorption spectra typical of ommochromes. Colored vesicles, of unknown function, also were found in the cytoplasm of the retinular cells. The intrarhabdomal filters appeared to act as long-pass spectral filters, and had maximum optical densities in situ of 0.94 to 11.1. 3. A variety of visual pigments were found in both species, each in a specific retinal region. Their maximum absorption peaked at wavelengths from 400 nm to well beyond 530 nm. 4. Spectral sensitivity functions of all retinal regions were estimated. In both species, each of the 4 most dorsal ommatidial rows of the central band had a pair of narrow spectral sensitivitity curves, usually separated by 50 to 75 nm. These 4 pairs covered the spectrum from below 400 to beyond 650 nm. The other 2 rows of the central band had identical, broad sensitivity functions. Spectral sensitivities of all peripheral ommatidia in each species were identical, but different from any region of the central band. 5. These stomatopod species have retained the typical crustacean layered rhabdoms in the peripheral retina and the 2 most ventral rows of the central band, but have converted the photoreceptors of the 4 dorsal rows of the central band into as many as 8 narrowly tuned spectral classes. This design could serve a high-quality hue discrimination system.