Redescription and designation of a neotype of Temnocephala talicei Dioni, 1967 (Platyhelminthes: Temnocephalida).

Temnocephala talicei was described from Uruguayan material found mainly on Aegla prado. Its original description was based principally on its distinctive penial stylet, and, therefore, many aspects of the species anatomy that are now important in the taxonomy of the genus were not contemplated; type specimens were never designated; and the material used to describe the species has been lost. The present work provides a redescription of the species based upon material collected from the type host and in the type locality. Given the possibility of confusion in its identification, and in order to preserve its taxonomic stability, a neotype of T. talicei is designated. The closest species to T. talicei is Temnocephala mertoni, from which it can be separated by the presence of conspicuous intestinal septa, a markedly asymmetrical sphincter in the vagina, markedly lobed testes, a straight penial stylet with a non-sinuous distal portion of the shaft, a characteristic large, 'mouthpiece'-shaped introvert without discrete thickenings, and approximately 10 crowns of well-developed spines of decreasing length placed throughout the whole extension of the introvert. A comparison of material from Uruguay, Argentina, and Paraguay shows that there is little variation in the morphometry of the species. Finally, a comparison of the post-tentacular syncytia of T. talicei and T. mertoni shows that this is not always a species-specific character.

A new Paravortex (Platyhelminthes, Dalyellioida) endoparasite of Mesodesma mactroides (Bivalvia, Mesodesmatidae) from Uruguay.

Many species of turbellarians (Platyhelminthes) are known to live associated with other organisms, especially invertebrates, as commensals or parasites. The family Graffillidae (Rhabdocoela) includes two genera that parasitize mollusks, Graffílla and Paravortex. Within the latter genus, six species were described as associated with mollusks. In other instances, unnamed Paravortex species were mentioned as parasites of other bivalves and of the body surface of fishes. In the present work, a new Paravortex species that was found in the intestine of Mesodesma mactroides from the Atlantic coast of Uruguay is described. In addition, a bibliographical revision of the known Paravortex species with their respective hosts, location, and distribution is made. Paravortex nicolli, described by Szidat for the Argentinean coast, is mentioned for the first time after the original description, and the authorship and date of description of Paravortex tapetis Noury-Sraïri 1989 are elucidated.

Monogeneans from Pangasiidae (Siluriformes) in Southeast Asia: I. Five new species of Thaparocleidus Jain, 1952 (Ancylodiscoidinae) from Pangasius pangasius, P. kinabatanganensis, P. rheophilus and P. nieuwenhuisii.

The examination of gill parasites from Pangasius pangasius (Hamilton, 1822); P. kinabatanganensis Roberts & Vidthayanon, 1991; P. rheophilus Pouyaud & Teugels, 2000 and P. nieuwenhuisii (Popta, 1904) (Siluriformes, Pangasiidae) in Southeast Asia revealed the presence of six species of Thaparocleidus Jain, 1952 (Monogenea, Ancylodiscoidinae). One has been previously described from P. pangasius: T. pangasi (Tripathi, 1957). The other five are new species: T. chandpuri n. sp. from P. pangasius; T. bahari n. sp. and T. sabanensis n. sp. from P. kinabatanganensis; T. redebensis n. sp. from P. rheophilus and T. mahakamensis n. sp. from P. nieuwenhuisii.

Patterns in metazoan parasite communities of some oyster species.

Metazoan parasite communities of Crassostrea gigas and Ostrea edulis from Great Britain, Crassostrea virginica from Mexico, and Saccostrea commercialis from Australia are described and summarized in terms of species composition, species richness, total number of individuals and dominance. Metazoan parasite communities in all host species were composed of turbellarians and the metacercarial stage of digeneans, with the exception of S. commercialis where only metacercariae were found. Arthropods, including one copepod and one mite species, were present only in British oyster species. All metazoan parasite communities of oysters had few species and low density of individuals. Richest communities were found in C. virginica at both component and infracommunity level. The least diverse component community occurred in S. commercialis. Infracommunities in O. edulis and S. commercialis never exceeded one species per host. The host response against parasites is suggested as the principal factor responsible for depauperate parasite communities of oysters. Environmental factors characteristic of tropical latitudes are likely to have enhanced both the number of species and the densities of parasites per host in the infracommunities of C. virginica.

Life history of the nematode Rhabdochona hellichi, a parasite of the barbel in the Jihlava River, Czech Republic.

From April 1992 until June 1993, the seasonal dynamics of Rhabdochona hellichi (Srámek, 1901) in its definitive host, the barbel (Barbus barbus), was studied in the Jihlava River (the Danube basin), Czech Republic. The parasite occurred in barbel throughout the year (overall prevalence 93% and intensity of infection 1-1384 [mean 78] nematodes per fish), but there were distinct seasonal fluctuations in prevalence and mean intensity values associated with the parasite's seasonal cycle of maturation. Prevalence was very high (usually 100%) during most months of the year, while lowest values were recorded in August and October. The highest values of mean intensity occurred in April. Both prevalence and mean intensity values increased with the body length of the hosts. The parasite exhibited a distinct annual cycle of maturation with egg-producing females present only from June until August, whereas larvae occurred in barbel mostly from September until April of the next year. Trichopteran (caddis-fly) larvae of the genus Hydropsyche (H. angustipennis and H. pellucidula) were found as natural intermediate hosts of R. hellichi (prevalence 4%, intensity 1-10 nematode larvae). The strictly seasonal maturation of this nematode may be associated with the temperature regime in the locality and seasonal cycles of maturation of its intermediate hosts.