Some ultrastructural features of the nuchal organ of <i>Daphnia magna</i> Straus (Crustacea: Branchiopoda)

Abstract

The ultrastructure of the nuchal organ of first instar of Daphnia magna is similar to that described in the literature for presumed ion-transporting tissues in other crustaceans. The apical and basal plasma membranes are extensively amplified through microvilli and infoldings; mitochondria are abundant and distributed unequally between the two types of cells (dark and light) composing the organ, more being present in the dark cells. The two cell types differ also in the type of microvilli projecting from their apical surface. In proecdysis these microvilli are replaced by much smaller ones which are associated with the deposition of the new cuticle.