ИСТИНА

Jaws are widely distributed among Trochozoa and presented by a cuticular structure formed by ectodermal epithelium in the buccal cavity. All classes of mollusks, except Polyplacophora have numerous representatives having different jaws. General morphology of gastropod jaws is well studied and structural characters (number, form and type of jaw plates) are used for taxonomy and cladistic analysis. At the same time the ultrastructure and type of jaw growth are unknown for Gastropoda that makes their comparison to other groups of Trochozoa impossible. The general morphology and ultrastructure of the jaws has been studied for nine species of Prosobranchia (Patellogastropoda (8 species) and Vetigastropoda ([Puncturella naochina])) and one species of Opistobranchia (Gymnosomatidae [Clione limacina]). Dorso-lareral jaw of Patellogastropoda has two symmetric parts, connected medially. Jaws of Patellogastropoda demonstrate different modifications from simple thin plate to thickened plate. Jaw of P.naochina composed of plate with numerous spines on the edge similar to opistobranch jaws with rodlets. The jaw complex of [C.limacina] consist of two symmetric parts (hook sacs). According to our data in morphology on the ultrathin level all jaws of investigated species are cuticular structures formed by ectodermal epithelium that squamous with short microvilli throughout of jaw except frontal part where cells with long microvilli. The place of growth located on frontal edge of jaw. Our data demonstrate that epithelium cells that format the jaws, possess comparatively long microvilli and the jaws continue to grow throughout the animal’s life. No evidence of shedding or replacement the jaws was found. The histogenesis of jaw formation in studied gastropods is similar with the polychaete one, except the type of jaw formation known for maxillae in fam. Dorvilleidae.