According to the latest revision of the genus Microsomacanthus Lopez-Neyra, 1942 (Cestoda: Hymenolepididae), most parasites of ducks and gulls are assigned to two subgenera that differ morphologically and biologically: the nominative taxon M. (Microsomacanthus) and the new taxon M. (Leuckartсohnacanthus) Galkin, Regel, 2010. Species that have no place in these taxa remain, however, within the genus Microsomacanthus s. l. Molecular-genetic analysis of 9 Microsomacanthus species showed the presence in NJ-phylogenetic tree of nucleotide sequences of a fragment of the 18S rRNA gene of two clades. One of them is formed by 3 species of the subgenus M. (Microsomacanthus), another one – by 5 ones of M. (Leuckartсohnacanthus). Haplotype from Microsomacanthus s. l. arcuata differs significantly from representatives of both haplogroups. This confirms the existence of at least two subgeneric taxa within the genus Microsomacanthus, as well as the presence of species worthy of their own subgenus.

The ultrastructure of the tegument of encapsulated tetrathyridia of the genus Mesocestoides Vaillant, 1863 (Cestoda, Cyclophyllidea, Mesocestoididae) from the liver of root voles Microtus oeconomus (Pallas, 1776) and the structure of the three-layered capsule surrounding them were studied for the first time. Several types of extracellular structures were noted on the surface of the tetrathyridia tegument: vesicles, fine granular material, and vacuoles. In addition, the phenomenon of shedding microtriches, which have expanded parts, was found. Host cells in contact with extracellular material show signs of destruction. A characteristic feature of the capsules surrounding the tetrathyridia is the reticular structure of the fibrous layer containing both native and degenerating inflammatory cells.

A fragment of 875 bp of the 18S rRNA gene was studied in 12 samples of Mesocestoides tetrathyridia from small mammals of 7 species collected in geographically distant localities. Five haplotypes were identified, differing from each other by 27 nucleotide substitutions in 24 sites. It has been found that the 18S rRNA haplotypes belong to two genetically distinct haplogroups. Molecular diversity indices were calculated for each of them. The conducted analysis allowed to suggest the following: 1) Mesocestoides sp. haplogroups A and B belong to two different species, but do not belong to any of the confirmed species of the genus; 2) the deletion of bp 729–747 and the insertion at site 761 of guanine can be regarded as a genetic marker for the species Mesocestoides litteratus.

A fragment of 875 bp of the 18S rRNA gene was studied in 12 samples of Mesocestoides tetrathyridia from small mammals of 7 species collected in geographically distant localities. Five haplotypes were identified, differing from each other by 27 nucleotide substitutions in 24 sites. It has been found that the 18S rRNA haplotypes belong to two genetically distinct haplogroups. Molecular diversity indices were calculated for each of them. The conducted analysis allowed to suggest the following: 1) Mesocestoides sp. haplogroups A and B belong to two different species, but do not belong to any of the confirmed species of the genus; 2) the deletion of bp 729–747 and the insertion at site 761 of guanine can be regarded as a genetic marker for the species Mesocestoides litteratus.

The article presents the data on structures of the nucleotide sequence fragments of the 12S ribosomal RNA gene (12S rRNA) for 19 tetrathyridia specimens of the genus Mesocestoides Vaillant, 1863 from representatives of 10 insectivore and rodent species from different regions of RussiaТs East and Alaska (USA). For the first time, the participation of three shrew species in the life cycle of Mesocestoides has been established. Nucleotide sequence fragments of the 12S rRNA gene have been analyzed phylogenetically. The researched tetrathyridia do not assumingly belong to any of the confirmed species of the genus; however, the identity of five of the 12S rRNA sequence fragments from micromammalian tetrathyridia and two nucleotide sequences of 12S rRNA from carnivorous mammals of Mongolia, placed in GenBank, has been established.

Приводятся первые данные по изучению тетратиридиев рода Mesocestoides Vail- lant, 1863 (Cestoda, Cyclophyllidea, Mesocestoididae) от красной полевки Myodes rutilus (Pallas) из Магаданской обл. методами молекулярной генетики. Получены полная нуклеотидная последовательность митохондриального гена cytb и частичная последовательность гена 12S рРНК Mesocestoides от естественно инвазированного хозяина. Фрагмент нуклеотидной последовательности 12S рРНК исследуемых тетратиридиев идентичен таковым из GenBank, определенным как M. lineatus (Goeze, 1782) от хищных млекопитающих Монголии. Га

The postembryonic development of most cyclophyllids within the intermediate host includes one invagination.This positions the remnants of the primary lacuna between the walls of the dense cyst.Some diplocysts, floricerci and ascocerci undergo two invaginations.In fully formed larvocysts belonging to these types, the remnants of the primary cavity are located between the walls of the additional outer envelope (exocyst).The presence or absence of a primary lacuna is the key characteristic used for metacestode classification.Nonetheless, the position of the primary lacuna during post-embryogenesis may also be important for understanding the evolution of the cestode lifecycle and phylogenetic relations among cyclophyllids.How to cite this article:

Morphological features of R a u s c h i ta e n ia a n c o ra (Mamaev, 1959), a cestode with atypicalmode of attachment («anchoring» in the wall of the host intestine), are considered. AtI he center of the overgrown scolex there is a rostellum, size of which is close to that of thedeveloped metacestode. Large suckers are composed mainly of loose parenchyma and fineradial muscle fibers. Fragments of host tissue are noted in the suckers’ cavity. Surface ofI he scolex is covered with large microtriches, which are in contact with the host tissue havingsigns of degradation. Distal cytoplasm is filled with vesicles coming from tegumentalcytons. Rostellar glands that are common to cyclophyllids are not found. Excretory canalscontain fluid (closer to the surface) and numerous lipid droplets (deeper located canals).

Two cysticercoids, belonging to ascocercus type, namely euascocercus and multicercus, were found in haemocoele of dragonfly larvae of the genus Aeshna from the lakes of the Magadan Province. The cysticercoid of Schistotaenia srivastavai Raush, 1970 (euascocercus) is formed of the outer (exocyst) and inner (endocyst) envelopes, containing the scolex and larval strobila. The outer and inner surfaces of the exocyst are represented by the tegument covered with microvilli. The microvilli of the outer tegument are restricted by the surface layer, consisting of granular and fibrillar material, and possess different structures at different stages of post-embryonic development. The multicercus of Mircia shigini (Konyaev et Gulyaev, 2006) is able to multiply asexually by the endogenous budding. The daughters' individuals are formed in the envelope of the multicercus that represents the tegument bearing microvilli. These microvilli are also restricted by the surface layer. The morphology and development of each individual cysticercoid of the multicercus is similar to those of euascocercus. The production of a great amount of cysticercoids, and the presence of the surface layer resembling the laminated layer of Echinococcus, relates multicercus to hydatid cysts.

The megalocercus of Dioecocestus asper (Mehlis 1831) from the haemocoele of dragonfly larvae possesses two envelopes: outer (exocyst) and inner (endocyst) ones. The exocyst contains the large endocyst and larval strobila with scolex attached to the latter. Outer and inner surfaces of these envelopes are organized as the tegument and have some structural differences. The exocyst is covered with slender microvilli. Its outer tegument contains numerous mitochondria; the inner one is filled with lipid droplets released into the exocyst's cavity. The well-developed protonephridial (excretory) system consisting of flame cells, collecting ducts and canals is the unique feature of the exocyst, noted for the first time. Thick (more, then 50 microm) distal cytoplasm of the outer tegument of the endocyst is the place of accumulation of uniform globules looking like a hyaloid layer. This outer layer together with underlying fibrous layer (up to 20 microm), apparently, protect the scolex and larval strobila during the transfer through feather clump in the stomach of grebes, definitive hosts of D. asper. Muscle cells of both envelopes retain their synthetic activity even in the fully developed metacestode. Probably, they are the main structural element, which produces fibers of the extracellular matrix and maintains the integrity of protective envelopes of the megalocercus.

The scoleces of Wardium chaunense penetrated into the intestinal wall of a snipe (Gallinago gallinago) were examined by light and transmission electron microscopy for the first time. Naturally, the scolex is characterised by a shorter length in comparison with when it is removed from the host. Ultrastructural characteristics of the main parts of the scolex, such as suckers, rostellum and rostellar sac are reported. Partial degradation of the radial muscles of the suckers is clearly recognised; this can be the result of a deep penetration of the scolex into the mucosa and subsequent loss of attachment function by suckers. The muscular walls of the rostellum and rostellar sac have a structure of the same type: an outer longitudinal layer of muscles is separated from the inner circular one with a thin basal matrix, which, also, surrounds each muscular fibre of the circular layer. Circular fibres consist of mutually perpendicular myofibrils, connected with the basal matrix by hemidesmosomes. Microtriches, covering the tegument, vary in shape in different regions of the scolex. They are absent on the apical part of the rostellum, and are slightly curved and can be considered as belonging to the fixative type on the suckers. Special sensory endings with a dense central body and without cilia are situated at the distal cytoplasm of the tegument of the suckers. Two glands, having the same syncytial structure, are disposed inside the rostellum and rostellar sac. Erythroid granules produced by the glands are released during an apocrine process into the host–parasite contact zone. Secretions of the cestode tegument in the form of vesicles and bubbles of granular material were also observed. It is suggested that the scolex attachment method of W. chaunense has the tendency of ‘anchoring’, which is an irreversible attachment used by some cestode parasites of the snipe.

Morphogenesis of the true ascocercus (euascocercus or euascocysticercoid) was studied in Schistotaenia srivastavai, a relatively rare parasite of the Red-necked Grebe Podiceps griseigena, and of intermediate hosts, damselfy and dragonfly larvae, in the Okhotsk-Kolyma region. Stages of postembryonic development were reconstructed by the material from spontaneously infected dragonflies' larvae, which corresponded to the published data on the development of metacestodes from the genus Tatria s. l. studied by Mrazek (1927) and Rees (1973). The euascocercus is the most widespread morphological modification of ascocysticercoids among Schistotaeniidae. According to Gulyaev (1989) and our data, the species of the family (the genus Mircia) have also a polycephalic modification of the ascocercus, or the multicercus. It represents a maternal individual that is filled with numerous small filial cysticercoids during the postembryonic development. These cysticercoids are formed of individual buds in the outer wall; later on, they are gemmated into the primary cavity of the maternal individual. Consequently, each daughter individual possesses its own single-layer exocyst, homological to the inner layer of the two-layered exocyst of the other ascocerci. Supposedly, exocyst's outer layer of monocephalic ascocerci is homologous to the outer wall of multicercus' maternal individual. Finally, diagnostic features of the third modification of ascocerci, namely megalocercus, described in the uniquely large metacestode Dioecocestus asper, corresponds to the characteristic of the metacestode Schistotaenia tenuicirrus, studied by Boertje (1975). S. tenuicirrus differs from D. asper in the spiral configuration formed on the entire surface of the endocyst (in D. asper, only on its dorsal side), and in a low number of proglottids in the larval strobile (D. asper possesses a multisegmental strobile). The reason, why so large protective envelopes (exo- and endocysts) develop in S. tenuicirrus with relatively small size of prospective body, remains unclear. Thus, life cycles of Schistotaeniidae represent all three modifications of the ascocerci: the true ascocercus (Shistotaenia, Tatria, Ryjikovilepis, Joyeuxilepis), the multicercus (genus Mircia), and the megalocercus (S. tenuicirrus).

: Metacestodes Dioecocestus asper (Cyclophyllidea) habe been found in larvae of dragonflies Aeshna spp. (Odonata, Anisoptera) from the lakes of the Upper Kolyma and northern Okhotsk seaboard basins (3.8 +/- 0.46 % of n = 1730 and 0.09 +/- 0.09 % of n = 1065, respectively) for the first time. Thus, participation of dragonflies in lifecycle of Dioecocestidae has been proved. Larvagenesis of D. asper (from spontaneously infested hosts) have been retraced from the stage of primary lacuna up to fully-developed metacestode. Process of development of the metacestode D. asper includes two invaginations. The first one follows the start of exogenous formation of undifferentiated anlage of the cystoscolex; as the result, the latter settles to the bottom of the forming two-layered exocyst homologous to the cercomer. Subsequent development of the prospecive part and the endocyst occurs in the closed amniotic cavity of the sacciform exocyst, the back pole of which preserves embryonic hooks and the front pole possesses the invaginational channel. At the stage of early scolexogenesis, the endocyst with the anlage of the strobila and the scolex separates from the exocyst and the excretory atrium forms on the back pole of endocyst. At the stage of late scolexogenesis, the formation of the larval strobila (differentiation of the sex) is completed and the second invagination starts. Strong retractors pull bottom of the stribila into the endocyst; simultaneously, the front part of it is also turned inside. The invaginational pore of the endocyst of fully-developed metacestode D. asper remains open; the scolex with the most part of the strobila is located outside the endocyst in the cavity of the exocyst. The encystment of the metacestode occurs when the temperature rises up to 40 degrees C (i. e., reaching the temperature of the definitive host). Morphogenesis of the uniquely large (among the cyclophyllid metacestodes developing in the invertebrate intermediate host) metacestode D. asper lasts for about two--three years and is associated with the developmental terms of the intermediate host, the larva of the Aeshna dragonfly, in climatic conditions of the Far North-East of Asia. Early stages of morphogenesis of D. asper were noted at the dragonfly larvae of the age of 0+ (at September) and 1+ (at June), and fully-developed metacestodes, only at elder ages. Owing to the extremely large size of D. asper metacestodes we refer them as a specific modification of cysticercoids: a megalocercus (Megalocercus). Common features were noted in the structure and morphogenesis of D. asper megalocercus and ascocerci of Schistotaeniidae. High morphological similarity of these metacestodes and their development in relative taxonomic groups of intermediate hosts, larvae of amphibiotic insects (the dragonfly larvae, and occasionally the larvae of mayflies or water-bugs), prove their belonging to the same philogenetically related group of metacestodes Cyclophyllidea, emerging independently from other groups of cysticercoids. We suggest naming this morpho-ecological group of larvocysts as ascocerci (or ascocysticercoids). The use of the name "ascocercus" as nominal nomenclature for group of larvocysts supposes the change of the name "ascocercus Schistotaeniidae" to "euascocercus".

Investigations were undertaken using light and transmission electron microscopy to clearly delineate the morphology of the cercomer, i.e. the protective envelopes and tail appendage, in cysticercoids of Microsomacanthus paraparvula, which develop in the haemocoel of the caddisworm Grensia praeterita (Insecta: Trichoptera). Two protective envelopes, the exocyst and endocyst, were identified. The non-cellular exocyst is found to consist of granular material and of thin, dense membrane-like layers, which are located parallel to each other. The exocyst of the mature metacestode tightly adjoins the outer surface of the endocyst, containing prospective parts (the scolex and the neck), except for the areas at its poles. A long tail appendage is located outside the exocyst. Evidence was found to indicate the existence of active synthetic processes occurring in the tail appendage. Non-cellular exocysts are widely distributed within metacestodes of the families Hymenolepididae and Dilepididae, and, presumably, are formed by means of glandular secretions from the oncosphere, given the early appearance of non-cellular exocysts in ontogeny.

This study was designed to provide information on the ultrastructural traits of the cirrus sac of the male strobila of the dioecious cyclophyllidean tapeworm, Shipleya inermis Fuhrmann, 1908 from the small intestine of long-billed dowitchers, Limnodromus scolopaceus, in Chukotka, Russia. The cirrus sac is characterised by a thick muscular wall (comprising about 20 layers of longitudinal muscles) with the muscle cells being located outside the wall along the peripheral muscle layer and the presence of a thick, fibrillar septum inside the sac along the inner muscle layer of the wall. The epithelium of the intrabursal ducts is syncytial and has sunken perikarya. The ejaculatory duct is characterised by surface luminal microvilli and a large number of the sunken perikarya producing electron-dense secretory granules, which discharge into the duct lumen as an apocrine secretion. The cirrus is armed with two types of sclerotized structures formed by its epithelium, hooks of about 25 μm in length and microthrix-like structures on its luminal surface. The hooks are sigmoid in shape, have a blade circular in transverse section and about 3.5 μm in width, and taper at both extremities. The hook body consists of moderately electron-dense material mixed with a more electron-dense material and an electron-lucent core. The hook roots lie within the cirrus epithelium, where their lateral margins are composed of a thin covering of electrondense material with narrow lateral extensions. The usefulness of the ultrastructural characters of the cirrus sac as indicators of phylogenetic relationships within the Eucestoda is discussed.

The morphology of the rostellar sac gland in juvenile (from a thin intestine of pintail) and adult (attached to a cloaca wall) cestodes Cloacotaenia megalops (Nitzsch in Creplin, 1829) is studied for the first time.Fixation of the adult parasites to a cloaca wall is carried out by means of powerful suckers; the apical pit, a homologue of rostellum, is a place for secret release from gland.It represents the group of specialized tegumentary AEåëåçà õîáîòêîâîãî âëàãàëèùà Cloacotaenia megalops (Cestoda: Hymenolepididae)

Fine structure of rostellar glands has been studied in two cestode species different from one another by the level of rostellum development. Secretion of the rostellar glands and rostellar sheath of Dichoanotaenia clavigera are characterized by different morphology, as well as different sites and ways of secretion. In Platyscolex ciliata morphological differences of the secretion of the rostellar sheath gland in the sites of synthesis and excretion were revealed. Possible causes of the morphologically different types of secretion in the rostellar glands of cestodes are discussed.

The ultrastructure of the tegument of R. ancora penetrating into snipe's gut wall is described. Four different tegument areas - the sucker, the scolex, the neck zone and the part of strobila, which is lokalized outside the capsule are distinguished. Distinctions in the microtriches structure and secretory inclusions depends on the mode of cestode fixation and the host-parasite interaction.