An ultrastructural study of the eye of Gomphiocephalus hodgsoni, a collembolan from Antarctica

Abstract

The collembolan Gomphiocephalus hodgsoni is one of a few hexapods occurring in Antarctica. Male and female individuals do not differ with regard to their eyes. Both possess eight single-lens eyes. In the adults, each lens has a diameter of 10–12 μm and covers an almost spherical crystalline cone made up of four unequal moieties. When we accepted homogenous refractive indices, known from pterygote insect eyes, and then calculated the focal length of the dioptric apparatus, we found that light could be focused on the retina. The retinal cells of each eye are grouped in two tiers and surround the centrally fused rhabdom. Rhabdomeric microvilli, approximately 1.3 μm long, possess a diameter of 80 nm and are typically aligned in one direction. More proximally, however, two rhabdomeres with microvilli perpendicular to the larger, more distal, rhabdom appear. Signs of light-induced damage, despite the bright summer radiation in Antarctica, were not seen. Ricegrain-like screening pigment granules, measuring 0.8×0.45 μm in dimensions, densely surround each rhabdom and shield the cytoplasm of the surrounding cells. The orthogonal arrangement of the microvilli suggests that G. hodgsoni could be sensitive to light-polarization. This ability might be of importance in detecting tiny amounts of meltwater in close proximity to the insect.