Ultrastructure of epidermal sensillae in three species of acoela

Abstract

© INVERTEBRATE ZOOLOGY, 2019. The investigation of the cellular organization of Acoela is of great interest for evolutionary morphologists and neurobiologists, since within this group we can observe the various stages of the formation of the nervous system and sensory organs characteristic of higher Bilateria. However, up to date the ultrastructure of epidermal sensory structures was described only for a relatively small number of acoel species. In the present work, four types of monociliary receptors were found in the epidermis of three species of this taxon (Otocelis rubropunctata, Symsagittifera japonica and Amphiscolops sp.). In the epidermis of O. rubropunctata there are three types of receptors - sensillae with a thin rootlet (with microvilli and without them), sensillae with a thick rootlet and receptors without a rootlet with stereocilia. In S. japonica the sensillae without a rootlet and with two circles of microvilli were found. Finally, in Amphiscolops sp. the sensillae with a thick rootlet and receptors without a rootlet with stereocilia were described. The distribution of certain types of ciliary receptors in various Acoela species is analyzed and their classification is proposed.