Does age matter in studying the crustacean eye?

Fifty randomly selected publications dealing with aspects of crustacean vision had their Materials and methods sections examined. In half of the articles gleaned, only the name of the animal under study was given; the other half mentioned ''adult'' or ''mature'' animals; twelve papers provided information on size or age of the experimental animal and six gave the sex. In Petrolisthes elongatus, rhabdom microvilli not only become more regular in outline as the animal grows, but also decrease in diameter from 90.4 +/- 21.2 nm in crabs of 5.0-8.9 mm carapace length via 86.6 +/- 13 nm in crabs of 9.0-12.9 mm carapace length to 79.7 +/- 7 nm in crabs of 13.0-16.9 mm carapace length. Approximately 400 cross sectional diameters of microvilli from identical regions in four eyes of each size class were measured and provided the basis for Anova-, Levene-, and t-tests. The three size classes possess microvilli of significantly different diameters and standard deviations. Our observations show that investigators of the crustacean photoreceptor have frequently neglected to consider the size of their experimental animals, but that this practice should not be continued as the now documented changes in microvillus diameters may influence the amount of visual pigment present and, thus, the photoreceptor's sensitivity to light.