The number that counts. Phylogenetic implications of the number of nurse cells in ovarian follicles of Coleoptera-Adephaga

The structure of polytrophic ovarioles in both Geadephaga and Hydradephaga is reviewed. Particular attention is paid to the significance of various morphological features and their bearing on the phylogeny of Adephaga. It is concluded that the number of nurse cells in the egg chambers is a valuable character in clarifying the phylogenetic relationships. The comparative analysis of the organization of egg chambers in aquatic and terrestrial adephagans, combined with other data suggests that a relatively small and constant number of nurse cells is a plesiomorphic condition for the Adephaga. This conclusion supports the notion that Haliplidae and Gyrinidae stand close to the ancestral stock of adephagous beetles.