ИСТИНА

New data on ultrastructure of Tricoma albimaris from the White Sea, North Russia are presented. Body cuticle consists of main rings covered with desms (thickenings) separated with interzones. The desms are built by concretions. The cuticle itself is structurally simple and thin, equal in thickness in main rings and interzones. Short finger-like projections arise from the cuticle into the desms - probably, the projections function in desm building. However, neither pores or canals in the cuticle nor indications on secretory activity in epidermal cells were revealed. Large vesicular amphids are covered with thin cuticle with indistinct radial striation. Cavity (fovea) of the amphid is filled with liquid substance and bundles of ciliary processes within. Phasmata, peculiar round paired lateral organs on the tail are open pits filled with transparent substance with ciliary processes; a nerve comes out anteriorly from the bottom of the pit. Ocelli, other highly peculiar organs of the most desmoscolecids including even deep-sea species, consist of electron-dense laminate material and lack any indication on receptors or nerve cells. Mouth opening small and round; small cheilostoma is formed by invaginated somatic cuticle and armed with teeth-like structures. Pharynx typical, with triangular internal lumen lined with thin cuticle. Midgut on the cross section consists of only two lateral cells; narrow internal lumen is filled densely with long microvilli arranged along the intestine axis. The project is supported by the grant RFBR 12-04-00781a. Keywords: Nematoda, Desmoscolecida, Tricoma albimaris, ultrastructure.