ИСТИНА

General morphology of annelid muscular system was well described using cLSM. Nevertheless morphology of muscular system of aberrant annelid group - Myzostomida is still poorly investigated and 3D reconstruction known only for one species. The muscular system of three species from genus [Myzostoma]: [M.ambiguum], [M.cf. gigas], and [M.polycyclus] was studied using cLSM and 3D reconstructions of muscles system were built. Main elements of muscular system are common in studied species; they are muscles of body wall, dorso-ventral muscles, muscles of introvert, parapodial muscular complex and muscles of lateral organs. Body wall musculature represented on the ventral side by longitudinal, transversal and ring fibers. Introvert can be divided into two parts: proximal part with strongly developed ring and radial layers, and distal part with thin longitudinal and ring fibers. Longitudinal muscles also covers entire introvert. Well developed retractors go from the dorsal and ventral side of introvert. Parapodial muscular complex consists of four pairs of muscle bunds going from the chaetae to body surface and one strong bund going to the center of body. All bundles join together and form star-shaped structure. Parapodia also include a muff of ring fibers enveloping the hook. Lateral organs have ring sphincter muscle and very thin oblique fibers enveloping the organ. Difference between studied species is in various degree of development of elements: in [M.cf. gigas] body wall musculature is the most developed, lateral organs have enveloping oblique fibers; in [M.polycyclus] parapodial muscles are strong but body wall is poorly developed; in [M.ambiguum] body wall and parapodial muscles are moderately developed, lateral organs have only ring sphincter muscle. Our results are similar with described for [M.cirriferum], but star-shaped structure, muff of ring fibers enveloping the hook and musculature of lateral organs are described for the first time.