New type of egg attachment structure in Ephemeroptera and comparative analysis of chorion structure morphology in three species of Ephemerellidae

Ephemeroptera eggs vary greatly in their morphology, a characteristic that has been used to solve systematic problems. The eggs of Ephemerellidae may be considered among the most studied in mayfly families, especially with regard to the number of species for which they have been described (approximately 32 species corresponding to 12 genera). However, this study provides new details of the egg morphology of three species of this family, Serratella ignita (Poda 1761), S. spinosa (Ikonomov 1961) and Torleya major (Klapalek 1905). The main finding was that the morphology and organization of the lateral attachment structures do not resemble the type normally associated with‘knob terminated coiled thread’ (KCT). The particular characteristics of this structure, never before described for Ephemeroptera, led us to propose a new type of attachment structure, the ‘multithread‐folded with terminal fibre cluster’ (MFT). We also provide a detailed description of the chorion morphology of the eggs of the three species, identifying a tear‐shaped variation in the oval sperm guide and confirming the type III polar caps in the two species of Serratella Walsh, 1862.