Microscopy and egg morphology of Mayflies

The chorionic structures of mayfly eggs can be categorized into three main classes (micropyles, attachment structures and chorionic sculpturing), according to their physiological function. Each class of structure shows a great variability as regards morphology, arrangement and distribution on the eggshell, and the combination of these features is the result of very particular chorionic patterns. The study of chorionic variability in both patterns and structures is very interesting for systematic purposes, because these features may be specific at different taxonomic levels. In addition, eggshell morphology allows us to identify female imagoes at species level when they lack valid taxonomic features, since eggs are completely formed in mature female nymphs. Light microscopy has already showed the great variability of the chorion structures in mayfly eggs and even allowed their classification. At present, this classification continues to be used as the basic reference in the morphological description of mayfly eggs, although it can only be done with SEM. Our morphological study on mayfly eggs, with both microscopy techniques, has allowed us to appreciate the beauty and complexity of the eggshell in this group of insects, as well as to describe new structures and to re-describe several aspects of chorion structures already known.