Photoreceptor spectral diversity in the retinas of squilloid and lysiosquilloid stomatopod crustaceans
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We examined the retinas of 2 species of stomatopods in the superfamily Squilloidea, Cloridopsis dubia and Squilla empusa, and 2 species of the super-family Lysiosquilloidea, Coronis scolopendra and Lysiosquilla sulcata, using microspectrophotometry in the visible region of the spectrum.
Retinas of all species included numerous photostable pigments, such as green reflecting pigment, hemocyanin, colored oil droplets, and vesicles. Both lysiosquilloid species also had intrarhabdomal filters within specialized photoreceptors of the midband.
Squilloid species contained a single visual pigment throughout all photoreceptors, with peak absorption at medium wavelengths (near 515nm). Retinas of lysiosquilloids contained a diversity of visual pigments, with estimated λmax values ranging from 397 to 551 nm.
Spectral sensitivity functions were estimated for the lysiosquilloid species based on estimates of visual pigment λnax, photoreceptor dimensions, and specific absorbances of the visual pigments and intrarhabdomal filters. Ommatidia of midband Rows 1 to 4 contained pairs of narrowly tuned spectral receptors, appropriate for spectral discrimination, while ommatidia of midband Rows 5 and 6, and all peripheral ommatidia, had broad spectral sensitivity functions.
Lysiosquilloid stomatopods have retinas that closely resemble those of gonodactyloids both structurally and in their visual pigment diversity. In contrast, squilloids have retinas that are much simpler. These differences appear to be related to the habitats and activity cycles of species belonging to the 3 major superfamilies of stomatopod crustaceans.
Key wordsPhotoreceptor Retina Spectral sensitivity Stomatopod Visual ecology Visual pigment
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