Annual dynamics and distribution of three Orthonectida species - Intoshia variabili, I. linei, Rhopalura littoralis - have been studied in the invertebrates in the White and Barentz Seas. Throughout years of observations Orthonectids show high stability, constant percent of infection and permanent location of the same spots. Mosaic pattern of their distribution has been revealed. Possible causes of difficulties in finding Orthonectids in nature are discussed.