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Simple geographical models using chronometric parasitic characteristics were applied to substantiate the determination of the host-loyality index of fleas. A mathematical relationship was inferred between the number of fleas feeding on a single rodent within a time unit and their quantily and the duration of an once-through parasitizing.

Eleven species of myobiid mites (Myobiidae) of the genera Myobia (7 species) and Radfordia (4 species) are recorded in a territory of the exUSSR. One new species is described: Radfordia (s. str.) mironovi sp. n. from the Apodemus flavicollis (Meichior) collected in the Crimea. A new diagnosis of the subgenus Myobia and a list of myobiid species recently recorded in the exUSSR are given.

The paper gives illustrated description of two new cestodes of the genus Pseudhymenolepis: P. crociduri sp. n. and P. spasskii sp. n. from the white-toothed shrew, Crocidura suaveolens collected in Turkmenistan. Specific differences of the new cestode species from closely related species are shown. Problems of morphology of alive eggs, the structure of the uterus and host specificity of some species of the genus Pseudhymenolepis are discussed.

Bielopolskaya (1952) mentions eider duck Somateria mollissima of the Murman Coast as a new host for Hymenolepis setigera (Froelich, 1789) (= Tschertkovilepis setigera). This tapeworm is known as a common parasite of geese. In the Zoological Institute one of Bielopolskaya's slides (N 1631) is presented. It is interesting to compare the morphology of eider duck's parasite with the same of Tsch. setigera from Anser anser. The investigation revealed that it is quite different. The scolex of Tsch. setigera resembles that of Diorchis, with short rostellum and oval suckers (fig. 1, a). The length of the rostellar hooks is 0.038-0.042 mm. They are of "rostel-loid" type as the guard is well-developed but much shorter than the blade (fig. 1, б). The topography of gonads is rather peculiar. The middle testis is situated antiporally to the median line of the proglottis, the female gonads lie just near the antiporal testis (fig. 1, в). The similar topography of gonads is in Wardoides nyrocae (fig. 2). Testes are present even in pregravid proglottids. Cirrus is very expessive, 0.3 X 0.045-0.05 in dimentions. The spines in its middle part attain 0.015 in length. The ovarium consists of 5-7 lobes (fig. 1, г). Uterus is sac-form, with numerous eggs in it. The length of the gravid strobile is more than 200 mm, it consists of several thousands of proglottids. Worms on the slide N 1631 undoubtedly belong to the genus Microsomacanthus as their scoleces have a rostrum (fig. 3, a, б). The length of rostellar hooks is 0.045 mm, their guard is rudimental (fig. 3, в). Gonads are slightly displaced to the antiporal side (fig. 3, г). Cirrus is 0.12 X 0.012-0.018 in dimentions, the longest spines attaining 0.006 mm are in its middle part. The ovary is small, 3-lobed; two lateral lobes are much more voluminous than the middle one. Testes are resorbed rapidly, so they are absent in the female zone of the strobile (fig. 3, д). The young uterus is tube-form, curved like a yoke, with its lateral ends turned onward. The number of eggs in it is restricted to about 40 (fig. 3, e). Pregravid strobile consists of 300 proglottids. Material of Bielopolskaya is identical to Microsomacanthus heterospinus Spassky et Jurpalova, 1964. This species described from eider duck of the Bering Sea in morphologically very close to the type species of the genus Microsomacanthus, M. microsoma (Creplin, 1829). However, the precise characteristic of M. microsoma is lacking. So we preliminary redetermine the material from the Barents Sea eider ducks as M. heterospinus. Deep distinctions observed between Tsch. setigera and M. heterospinus do not permit to consider them in the limits of one genus. The diagnosis of the genus Microsomacanthus given by Chaplinski, Vaucher (1994) is too vague. To our opinion, the validity of the genus Tschertkovilepis Spassky et Spasskaja, 1954 with the type species Tsch. setigera is out of question.

The penetration glands of Triaenophorus nodulosus undertake great structure modifications during a life cycle. A pair of gland cells in oncosphere provided with specialized ducts degenerates and appears „de novo" during a morphogenesis process of plerocercoids. Most high specialized structure of penetration glands is reached in the invasion plerocercoid stage. A gland apparatus of the invasion plerocercoids consists of two types of gland cells, ducts of which open into the funnel-like depression. This depression is provided with special muscles to accelerate the excretion. In the incapsuled plerocercoids and adult worms the penetration apparatus is simplified. The penetration glands are represented by single cells situated in a parenchyma of scolex and in anterior parts of the worm body.

Ten ant species, namely: Messor structor, Formica cinerea armeniaca, F. cunicularia, F. fusea, F. rufibarbis, F. sanguinea, F. transcaucasica, Ctaglyphus aenescens, C. albicans armenia, Proformica pilosiscapus, were found to serve as supplementary hosts in spreading of Dicrocoelium lanceatum larvae. Among them, C. albicans armenia is a new host record, M. structor and F. cunicularia are reported as hosts for the first time for the Transcaucasus and Armenia republic respectively. A prevalence and intensivity of ant infection rate are evaluated. Ecological and faunistic characteristics of all examined ant species being recorded as D. lanceatum supplementary host in Armenia are compiled. Data concerning F. rufa occurrence and its experimental infection with D. lanceatum larvae seems to be questionable.

An immature specimen of Aspidogaster conchicola was recorded from Bithynia tentaculata collected in the Pleshcheyevo lake. A. conchicola was also found in bivalve molluscs Anodonta cygnea, Unio pictorum and Crassiana crassa in the Kotorosl river and Sutka river (Yaroslavl region). A gastropode mollusc is recorded as a host of A. conchicola for the first time in Europe. Points of records and hosts of A. conchicola in exUSSR are listed. A host specificity and distribution of this parasite in the Unionidae and in gastropod molluscs are discussed.

The fine structure of the scolex nervous system of the Triaenophorus nodulosus was examined. The ultrastructures of ganglions, central comissure, and bothrium nerves are described. Five ultrastructural types of neurons, processes of muscle cells and cells of excretory ducts have been observed. The synaptic contacts in neuropile of ganglions and bothrium nerves are described in detailes. An interrelation of nervous and excretory systems, which is similar to the neuroglyal relations in high animals, has been recovered. The wall cell processes of excretory ducts cover the ganglions, pierce into neuropile and surround the groups of processes and neurons. The distribution of the serotonin (5-HT) in plerocercoids and adult Triaenophorus nodulosus was investigated. The distribution nervous system elements being immunoreactive to RFamide is shown in total specimens and semi-thin microscopic sections of adult worms. The presence of RF-immunoreactive (IR) synaptic vesicles with electron dense contents in presynaptic tips of assymmetric synapses in the region of hook muscles are shown by means of electron immunocytochemistry techniques.

An ultrastructure of microsporidia spores of Glugea anomala from Pungitius pungitius, G. gasterostei from Gasterosteus aculeatus, G. fennica from Lota lota, G. hertmgi from Osmerus eperlanus, G. acerinae from Gimnocephalus cernua and Glugea sp. from Perca fluviatilis is described. Similar spore organisation in these microsporidian species has been established. A conclusions about close phylogenetic relationships of species examined and homogeneity of the genus Glugea are proposed. Problems of species validity of G. anomala, G. gasterostei and G. weissenbergi from sticklebacks and microsporidian species from a common ruff and perch are discussed.

In ixodid tick collections of 1957, 1959, 1960 years from different regions of the Krasnoyarsk area the ixodid ticks Ixodes pavlovskyi, I. apronophorus, I. maslovi have been recorded for the first time. The latter species was previously known only by the male and female. The description of the I. maslovi nymph is given for the first time. In materials from the Bering's Isiand one female and three larvae of I. berlesei have been found on the Snow bunting Plectrophenax nivalis.

A new species, Blastocystis agrionemidis, was found in Horsfield's tortoise. Sizes of blastocysts in culture are 5-17.5 µm. Individuals oval and round shape were met more often, which diameter was 12.5-15 µm, the number of nuclei varies from 1 to 2, the central vacuole was colored up to Giemsa in dark-biue or grey-blue. Optimum temperature for cultivation is 18 ± 2°.

The microsporidia Eimeria alces Arnastauskiene, 1971 has been recorded from fecal probes of elks (Alces alces) in the Bryansk region. The oocyst measure 40.6 + 2.0 X 28.6 + 1.0 mkm.

Summary is absent.