In view of earlier results, suggesting a considerable stability in the number and distribution patterns of caudal papillae and papillae-like structures in the male of some ascaridoid species, these features are analysed more generally within the superfamily Ascaridoidea. They include the single pair of phasmids on the tail, four pairs of distal papillae some of which are considered in some cases to occur anterior to the level of the cloaca, two pairs of paracloacal papillae, a median papilla or plaque, and numerous pairs of proximal papillae some of which may be situated posterior to the level of the cloaca. The exceptions to this general pattern and the systematic and phylogenetic significance of caudal morphology are discussed.

Hatched, ensheathed third-stage larvae of Contracaecum osculatum, 300-320 microns long, were shown to be infective to copepods, to nauplius larvae of Balanus and to small specimens of fishes (sticklebacks, O-group eelpout). Other fishes such as gobies and small flatfishes became infected by ingesting infected crustaceans. Cod were infected by being given infected small fishes. In the crustacean paratenic hosts, little growth of the larvae occurred, if any. In the liver sinusoids of sticklebacks and gobies the length of most of the unencapsulated third-stage larvae had not even doubled within 6 months of infection. The fate of larvae (max. 2 mm long) given to cod via infected intermediate fish hosts was apparently decided by the size of the larvae only. Small larvae became encapsulated and eventually died in the liver and wall of the gastrointestinal tract. Larger larvae migrated to the liver parenchyma, where some grew to a length of as much as 10 mm. The growth of the larvae in sticklebacks was shown not to be affected by an increase in temperature (infected fish being transferred from 8 degrees to 14 degrees and 20 degrees C), by the intensity of infection and, partly, by the age of infection (e.g. some 2-week-old and 6-month-old larvae were of identical size). In the liver and mesentery of plaice the third-stage larvae developed via copepod paratenic hosts to infectivity (i.e. to more than 4 mm in length), showing that the life cycle may be completed with an optional paratenic invertebrate host and only one intermediate fish host.(ABSTRACT TRUNCATED AT 250 WORDS)

The fine structure of the mature spermatozoon of the pseudophyllidean tapeworm Eubothrium crassum, a parasite of salmonid fishes, has been studied by transmission electron microscopy for the first time. The mature spermatozoon of E. crassum is filiform and tapered at both extremities. It contains two axonemes of unequal length showing the 9 + "1" pattern of Trepaxonemata. The anterior extremity exhibits a crested body 50-100 nm thick. It spirals around the outside of the anterior region of the spermatozoon. The nucleus is electron-dense, exhibiting a fibrous appearance in its middle (the broadest) region. The cortical microtubules are of two types and are situated parallel to the spermatozoon axis. The cytoplasm is slightly electron-dense and contains numerous electron-dense granules in region II of the spermatozoon. A ring of electron-dense, centred microtubules surrounds the axoneme, together with the underlying ring of moderately electron-dense, subjacent submicrotubular material in region V. The anterior and posterior extremities of the spermatozoon lack cortical microtubules and contain a single axoneme. Our results reveal several peculiarities, in which the spermatozoon of E. crassum differs from those of other pseudophyllidean cestodes.

Contracaecum spp. are common parasites of seals and piscivorous birds. The world‐wide distribution which has been attributed to the species C. osculatum needs verification. In the present study thc intra‐specific variability of some taxonomically significant characters was studied in this species. Features analysed include the length and morphology of the distal end of the spicules, the number of proximal caudal papillae and the number of papillae in the region of the first 25 cuticular transverse striae anterior to the cloaca, delined as the Pts zone (precloacal transverse striae zone). The spicules reach their maximum length only in fully grown worms. while the morphology of the distal end of the spicule is determined early in the life of adult male worms. Included is a detailed analysis of the observed morphometric variability in the distal end of the spicule. The number of cuticular transverse striae in relation to papillae in the Pts zone remains constant in different length classes of the parasite. A redescription of the parasite is provided, bascd on material obtained from grey seals in the Baltic Sea, to serve as a basis for discussions on the taxonomy of the genus.

Contracaecum sp. larvae (L3) from fish were identified using nucleotide sequences of the internal transcribed spacers ITS-1 and ITS-2 of the ribosomal DNA. The nematode larvae originated from fish in a freshwater situation (crucian carp Carassius carassius, from Selment Wielki Lake in Mazury, northeastern Poland) and a brackish-water region (Caspian round goby Neogobius melanostomus from the Baltic Sea, Gdafisk Bay at the Polish coast). Two strains (Contracaecum rudolphii A and B) of Contracaecum rudolphii senso lato, a parasite common at the adult stage in fish-eating birds, were identified. In fish from the freshwater site, only the strain temporarily designated C. rudolphii B was identified; in the brackish-water region, both strains were found, suggesting that fish serve as paratenic host for both genotypes. Contracaecum rudolphii sensu lato has been recorded in several species of fish-eating birds in Poland, particularly in the great cormorant, Phalacrocorax carbo, in which the abundance is highest. The results, although based on a restricted number of larvae, suggest that the life cycles of both genotypes can be completed in the Polish region and that at least one of them, C. rudolphii B, can develop both in fresh and brackish water.

Studies of the morphology of Ascaris suum larvae developing in the egg during embryonation in vitro at room temperature showed that 2 molts take place within the egg. The first larval stage (L1) appeared in the egg after 17-22 days of cultivation, the first molt to the second larval stage (L2) took place from day 22 to day 27, and the second molt to the third larval stage (L3) started on day 27 and continued during the 60-day observation period. Infectivity of the eggs was studied by oral egg inoculation in mice and showed that the L3 are the infective stage for mice. Molting to the L3 stage occurs gradually over a period of 2-6 wk, and it is recommended to have an additional maturation period so the infectivity of an egg batch may reach maximum level.

The otariid seal parasite Contracaecum ogmorhini Johnston & Mawson, 1941 is redescribed based upon new material and the type specimens. The geographical records of this species indicate that it has an antiboreal circumpolar distribution with an isolated population on the south‐west coast of North America. The species is considered to be morphologically more similar to Contracaecum spp. from birds than to those from phocid seals: its possible evolution is commented upon. The material identified as C. osculatum (Rudolphi) by Flores‐Barroeta et al. is considered conspecific with C. ogmorhini, thus suggesting that it is this species, and not C. osculatum, which is responsible for abnormal tissue migration and brain damage in pinnipeds.

Nuclear-encoded large-subunit ribosomal DNA sequences were used to infer a phylogenetic hypothesis for 17 taxa (16 nominal species) of the genera Contracaecum and Phocascaris. Phylogenetic trees based on these data have been used to assess the validity of the taxonomic distinction between these genera, which was based on the presence or absence of certain structural features, rather than on explicit hypotheses of evolutionary history. Phylogenetic hypotheses based on parsimony, likelihood, and neighbor-joining analyses of these sequence data strongly support the hypothesis that species of Phocascaris are nested within the clade of Contracaecum species hosted by phocid seals, and are more closely related to species of the Contracaecum osculatum complex than to other Contracaecum species. Alternative tree topologies representing Phocascaris as not nested within the C. osculatum complex were significantly worse interpretations of these sequence data. Phylogenetic analysis also provides strong support for the monophyly of all taxa (Contracaecum and Phocascaris) from phocid seals, which is consistent with Berland's (1964) proposal that such species form a natural group; however, his proposal to recognize all species in phocid seals as Phocascaris, with all species from birds as Contracaecum would result in a paraphyletic Contracaecum, according to the molecular phylogenetic hypothesis.