Abstract
BackgroundWithin the genus Crepidostomum Braun, 1900, identification of species and taxonomic decisions made only on the basis of adult morphology have resulted in great problems associated with evaluating actual diversity and validity of species. Life-cycle data, while equal in importance to adult characters, are scarce, controversial or incomplete for most Crepidostomum spp. In this study, rDNA sequences generated from adult and larval Crepidostomum spp. and some other allocreadiid species were analysed to reveal the diversity and phylogenetic relationships of the species and their host range. Detailed morphological description based on light microscopy, SEM tegumental surface topography and genetic data are provided for the poorly known trematode C. oschmarini Zhokhov & Pugacheva, 1998 found in the intestine of two teleost fish species, Barbatula barbatula (L.) and Cottus gobio L.ResultsWe characterized 27 isolates of adult and larval parasites. Based on newly obtained 28S and ITS1-5.8S-ITS2 rDNA sequences, new intermediate and final hosts were ascertained, and life-cycles clarified for some allocreadiids. New knowledge on the diversity and phylogenetic relationships of European Crepidostomum spp. was gained. The validity of C. oschmarini was verified based on comparative sequence analysis. Ophthalmoxiphidiocercariae of C. oschmarini were recorded in sphaeriid bivalves Pisidium (Euglesa) casertanum (Poli). Additionally, morphological differences between gravid specimens of C. oschmarini and other related species were observed.ConclusionsSpecies of the Allocreadiidae parasitizing fishes in Europe are distributed among two monophyletic genera, Allocreadium and Bunodera, and two paraphyletic Crepidostomum clades. A complex of Crepidostomum metoecus (syn. C. nemachilus), C. oschmarini and Crepidostomum sp. 2 clustered in one clade, and a complex of C. farionis, Crepidostomum sp. 1 and, probably, C. wikgreni in the other. Molecular data indicated that C. oschmarini and Crepidostomum sp. 2 presumably have a wide geographical distribution in Europe. The new data provided evidence that Crepidostomum is a more diverse genus than can be judged from morphological data and host switching in this genus may occur independently of fish-host phylogeny.
Highlights
Within the genus Crepidostomum Braun, 1900, identification of species and taxonomic decisions made only on the basis of adult morphology have resulted in great problems associated with evaluating actual diversity and validity of species
Most taxonomic decisions have been made based on adult morphology, it should be noted that a number of species are morphologically very similar and there exist only a few morphological features useful for distinguishing species [3, 4]
The Crepidostomum metoecus complex consists of C. metoecus
Summary
Within the genus Crepidostomum Braun, 1900, identification of species and taxonomic decisions made only on the basis of adult morphology have resulted in great problems associated with evaluating actual diversity and validity of species. Crepidostomum farionis (Müller, 1784) and C. metoecus Braun, 1900 are among the most common and widely distributed freshwater parasites of salmonid fishes in Europe. Reliable features for differentiating these two species were obtained only in the second half of the 20th century (see [7]) and formerly C. metoecus was frequently mistaken for C. farionis. Both species have been known by numerous synonyms (see [1, 8]). Prior to the present study, C. farionis and C. metoecus were the only representatives of the genus to have been recorded in Lithuania and neighboring regions [6, 9]
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