During the past twenty years, a number of molecular analyses have been performed to determine the evolutionary relationships of Onchocercidae, a family of filarial nematodes encompassing several species of medical or veterinary importance. However, opportunities for broad taxonomic sampling have been scarce, and analyses were based mainly on 12S rDNA and coxI gene sequences. While being suitable for species differentiation, these mitochondrial genes cannot be used to infer phylogenetic hypotheses at higher taxonomic levels. In the present study, 48 species, representing seven of eight subfamilies within the Onchocercidae, were sampled and sequences of seven gene loci (nuclear and mitochondrial) analysed, resulting in the hitherto largest molecular phylogenetic investigation into this family. Although our data support the current hypothesis that the Oswaldofilariinae, Waltonellinae and Icosiellinae subfamilies separated early from the remaining onchocercids, Setariinae was recovered as a well separated clade. Dirofilaria, Loxodontofilaria and Onchocerca constituted a strongly supported clade despite belonging to different subfamilies (Onchocercinae and Dirofilariinae). Finally, the separation between Splendidofilariinae, Dirofilariinae and Onchocercinae will have to be reconsidered.

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The review deals with the species of Rhabdiasidae Railliet, 1915 occurring in the Holarctic. Descriptions of 26 species from the genera Rhabdias Stiles et Hassal, 1905 (21 species), Entomelas Travassos, 1930 (4 species), and KurolonemaSzczerbak et Sharpilo, 1969 (1 species) are presented. Additionally, 5 species of Rhabdias are listed as species inquirenda, and 4 species are included into the review, since they have been reported close to south-eastern border of Palaearctic (the exact distribution is unknown). Keys to the Holarctic species and diagnoses of the genera are provided. An overview of the information on the biology, morphology and taxonomy of Rhabdiasidae is also presented, as well as the host-parasite list of Holarctic Rhabdiasidae.

Rhabdias bakeri n. sp. is described from specimens found in lungs of the wood frog, Rana sylvatica, from North Dakota. The new species has previously been mistakenly identified as Rhabdias ranae Walton, 1929, a common parasite of the leopard frog, Rana pipiens. The new species differs from R. ranae and Rhabdias joaquinensis Ingles, 1935 by the shape and size of pseudolabia, shape and size of buccal capsule, and wider esophageal bulb. Molecular analysis based on the partial sequences of nuclear 18S rDNA gene, complete sequences of internal transcribed spacer region, and partial sequences of 28S gene demonstrates clear differences between Rhabdias from Ra. sylvatica and Ra. pipiens, and supports the status of R. bakeri as a new species.

We studied variation in the structure of component communities of helminths in sand lizards, Lacerta agilis, from 30 localities in the Ukraine and Bulgaria. Thirty-five separate samples of lizards, with a total of 661 completely censused infracommunities, yielded 30 helminth species (4 cestodes, 10 trematodes, 3 acanthocephalans and 13 nematodes). In its range within the Ukraine, L. agilis serves as the final host for 13 species of which only 3 (S. lacertae, S. hoffmanni and P. molini) can be considered as lizard specialists. A characteristic feature of these helminth component communities was the large proportion of heteroxeneous helminth species for which L. agilis serves as paratenic host. Sand lizards in the meadow steppeland zone were primarily parasitized by larval helminths that represented a major proportion of the total number of all worms recovered while those sampled in the grassland/forest transition zone were characterized by substantially higher proportions of adult helminths using lizards as final hosts. However, L. agilis was parasitized by a much higher proportion of lizard specialists in the ‘typical' habitats of the meadow steppeland zone as opposed to those located in ‘marginal' habitats in the grassland/forest transition zone, where helminths were shared to a greater extent with amphibian hosts.

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