Ultrastructure of the Photoreceptors in the Pycnogonid species,Nymphon gracile(Leach), andPycnogonum littorale(Strom)

Abstract

In British pycnogonids the eyes are four in number and are sited on a tubercle which is situated on the dorsal surface of the cephalothorax. The shapes of the eye tubercles in some British species are described, together with the ultrastructure of the eyes in Nymphon gracile. The eye is simple with a cup‐shaped, non‐inverted retina similar to that found in a number of arachnids, with a single lens. The ultrastructure of the cuticle, hypodermal cells, tapetum, pigment cells and retinal cells is described. It is similar to that of other simple eyes from a variety of invertebrates.