Kamardin N.N.1, Sirenko B.I.2 2017. Ultrastructural study of the osphradia in Polyplacophora // Invertebrate Zoology. Vol.14. No.2: 140–147 [in English].
1 Saint-Petersburg Scientific-Research Centre for Ecological Safety, Russian Academy of Sciences, Korpusnaya Str., 18, St. Petersburg, 197110, Russia. E-mail: firstname.lastname@example.org
2 Zoological Institute of the Russian Academy of Sciences, Universitetskaya nab. 1, St. Petersburg, 199034, Russia. E-mail: email@example.com
ABSTRACT: The investigation of ultrastructure of osphradia in ten polyplacophoran species from suborders Acanthochitonina and Chitonina revealed a number of similar, primitive structures. In all specimens, each osphradium resembles a more or less isolated shaft or fold of specialized single-layered epithelium located in the mantle cavity immediately behind the last pair of gills. Ciliated, microvilliferous, and secretory supporting cells, as well as peripheral processes of receptor cells with several cilia forming the receptor surface of the osphradium were discovered. On the osphradial surface, there is no division into zones, which are characteristic of the osphradia in the gastropods. It is undoubtedly the organ of the chemical sense, performing the initial role of the interoreceptor and reacting to a change in the physico-chemical characteristics of the fluid in the mantle cavity (O2, pH, osmolarity, etc.). Perhaps, osphradium acts as a distant chemoreceptor in complex behavioral acts, such as homing. However, due to the large plasticity of the molluscs, it is possible to form other sensory structures, which, especially in primitive groups (for example: Lepidopleurida), can partially perform the osphrasdial functions. If we take into account the absence of osphradia and the presence of numerous parts of sensory epithelium in the mantle cavity of the most primitive forms of chitons belonging to the order of Lepidopleurida, then probably osphradia in the more advanced chitons, the Chitonida order, as an independently developed organ, possibly not homologous to the osphradia of other molluscs (Gastropoda, Bivalvia and some Cephalopoda).
KEY WORDS: ultrastructure, osphradium, Acanthopleura brevispinosa, Ischnochiton hakodadensis, Tonicella marmoreal, receptor cells.