The life-history of Mazocraes alosae Hermann, 1782 on one of its hosts, the Pontic shad Alosa immaculata Bennett, is described for the first time. This anadromous fish, which occurs off the coast of the Crimea and migrates from the Black Sea to the Sea of Azov and into the River Don for spawning, was studied throughout its migration and during all seasons. It is demonstrated that the period of reproduction of this monogenean is significantly longer than that reported for the population in the Caspian Sea, lasting from April to November with a peak in April-May, and continues both in the sea and the river. Experiments showed that water salinity does not limit the development of the eggs or the hatching of the oncomiracidia. Our data reveal that the abundance of M. alosae is not determined by the size or sex of mature fish and that shad of less than two years old can also be infected with this monogenean, although less frequently than older fish. The direction of the migration of A. immaculata, either from the Black Sea to the Sea of Azov and into the rivers or in the opposite direction, does not influence the number of monogeneans present on the host. The main factor affecting the dynamics of the abundance of this monogenean is season, and, as has been indicated previously in the Caspian Sea basin, there is a synchronisation between the parasite's life-history and both the host's spawning behaviour and the duration of its migration.
The external morphology of two bucephalid digenean parasites of Conger conger (Linnaeus) (Congridae, Anguilliformes) caught northwest of the Iberian Peninsula, Prosorhynchus crucibulum (Rudolphi, 1819) Odhner, 1905 and P. aculeatus Odhner, 1905, were studied using scanning electron microscopy (SEM). SEM techniques elucidated new external morphological details, mainly relating to the tegument and protruding organs, such as, in P. crucibulum, a papilla-like structure associated with the pharynx and, in P. aculeatus, the cirrus. The tegument bears scale-like spines, which in both species are arranged quincuncially. The spines of P. crucibulum are wider than long and cover the major part of the body and rhynchus. However, no spines were found in either the central apical depression of the rhynchus or in the middle of the ventral indentation. Also, spines were rarely seen on the tegument around mouth, around the genital aperture or close to the excretory pore. P. aculeatus has spines of a different shape, as wide as they are long and with a rounded margin. They cover the whole body and almost the entire rhynchus, but none were found in the middle of the rhynchus or on its neck region.
Three species of Magnibursatus Naidenova, 1969 are described from marine teleosts: M. skrjabini (Vlasenko, 1931), the type species of the genus, from the gobiid Zosterisessor ophiocephalus on the Bulgarian Black Sea coast; M. bartolii sp. n. from the sparid Boops boops off the Atlantic coast of Spain; and M. minutus sp. n. from the gobiid Neogobius eurycephalus on the Bulgarian Black Sea coast. M. bartolii differs from all other Magnibursatus species in its larger sinus-sac (length >250 µm, width >150 µm) and the more posterior location of testes. This species is also unusual in that it occurs in the branchial chamber and on the gills of its host. M. minutus is distinguished by the distinctly smaller dimensions of the body (length <1000 µm, width <200 µm), organs and eggs. These species are also distinguished from both M. caudofilamentosa (Reimer, 1971) and Tyrrhenia blennii Paggi et Orecchia, 1975. A key to the species of Magnibursatus is presented.
The surface structures and gland cells of the posterior rosette organ of Gyrocotyle urna Grube et Wagener, 1852, a member of the group presumed to be the most basal of the tapeworms (Cestoda: Gyrocotylidea), was studied by scanning electron and transmission electron microscopy. Surface structures on the outer (oriented away from the intestinal wall) and inner (in contact with the intestinal wall) rosette surfaces differ from each other and represent a transitional form between microvilli and microtriches typical of tapeworms (Eucestoda). The inner surface of the rosette possesses numerous glands. On the basis of the size and electron-density of their secretory granules, three types of unicellular gland cells can be distinguished. The least common type (Type I) is characterized by the production of small, round, electron-dense granules of about 0.3 µm in diameter, whereas another type of secretion (Type II) is formed from homogenous, moderately electron-dense, spheroidal granules of about 0.7 µm in diameter. The most common type of glands (Type III) is recognized by a secretion comprising large, elongate, electron-dense granules of about 1 µm long and 0.5 µm broad. The secretory granules of the three types of the glands are liberated by an eccrine mechanism and the gland ducts open via small pores on the inner rosette surface. The complex of secretory glands of the posterior rosette of G. urna is similar to those in the anterior attachment glands of monogeneans (as opposed to the types of glands present in other helminth groups). However, the tegumental surface structures of Gyrocotyle are supporting evidence for the relationship between the Gyrocotylidea and Eucestoda.