In the present study, phylogenetic relationships of European and Far Eastern representatives of the genus Aspidogaster Baer, 1827 were analysed: A. conchicola Baer, 1827, A. limacoides Diesing, 1834, A. ijimai Kawamura, 1915 and A. chongqingensis Wei, Huang & Dai, 2001. Based on ITS1-5.8S-ITS2 rDNA sequence data, an obvious differentiation was seen between specimens of A. limacoides sensu stricto from the European part of Russia and A. limacoides sensu Chen et al., 2010 from China (13.7%); the latter parasites were recognized as A. chongqingensis. Aspidogaster chongqingensis was more closely related to A. ijimai than to A. limacoides s. str. Specimens of A. ijimai from the Amur River, Khanka Lake (Russian Far East) and China were grouped into a single clade with low intra specific molecular differentiation (d = 0-0.3%). Specimens of A. conchicola from the European part of Russia, the Russian Far East and China also formed a single distinct clade. Genetic differentiation between European and Chinese samples of this species was two times lower (d = 0.45%) than between Russian Far East and European or Chinese samples (d = 0.96%), suggesting a long-term separate existence of A. conchicola in the Russian Far East.
In this paper, we review, continent by continent, the trematode fauna of freshwater fishes of the 'Old World', a vast area consisting of the Palaearctic, Ethiopian, Oriental and Australasian zoogeographical regions. Knowledge of this fauna is highly uneven and clearly incomplete for almost all regions, sometimes dramatically so. Although the biggest problem remains the completion of the 'first pass' of alpha taxonomy, there are in addition great problems relating to biogeography and elucidation of life-cycles. For the latter, molecular data, i.e. matching DNA sequences of larval stages and corresponding adults, may represent a powerful tool that should be used in future studies. Another challenging problem represents the existence of cryptic species and, in particular, considerable decrease of experts in taxonomy and life-cycles of trematodes.
Acanthobdellidans are unique in their organisation and phylogenetic relationships due to having transitional characters that combine features of oligochaetous and achaetous annelids. Alongside the relatively well-studied Acanthobdella peledina Grube, 1851, there is another member of the group, Paracanthobdella livanowi (Epshtein, 1966), with five rows of chaetae and an anterior sucker. It appears that the anterior sucker is weakly developed in small juveniles but acquires a deep cavity in adults. Smaller individuals of P. livanowi can be distinguished from A. peledina, which does not possess an anterior sucker, by the varying breadth of their chaetae. The mid-body segment consists of two doubled annuli in juveniles and is quadri-annulate in large individuals. In Kamchatka freshwaters, hosts of P. livanowi mostly include Salvelinus spp. and more rarely Gasterosteus aculeatus, Oncorhynchus mykiss and O. kisutch. New information on the distribution and the biology of P. livanowi is presented.
Genetic divergence and phylogenetic relationships of four species of the genus Crepidostomum Braun, 1900 sensu Caira, Bogĕa (2005) were revealed using partial sequences of 28S ribosomal RNA gene. Genetic divergence between C. cf. farionis (Muller, 1784) and C. nemachilus Krotov, 1959 was 3.1%, which corresponds to the mean value of interspecific divergence between Crepidostomum species. These two species, therefore, can be recognized as bonafide species. However, we found no genetic differences between 28S rRNA gene sequences of C. nemachilus and C. cf. metoecus Braun, 1900 in spite of considerable morphological and ecological differences. Maximal values of genetic p-distances were revealed between C. cf. auriculatum Wedl, 1857 and C. cf. farionis. Phylogenetic relationships of Crepidostomum spp. for which sequence data are available, along with species in other related genera (Bunodera Railliet, 1896 and Allocreadium Loss, 1900) showed a paraphyly of the genus Crepidostomum. Considerable differentiation of C. cf. auriculatum from other Crepidostomum species was revealed, which may reflect the original description of this species in a separate genus Acrolichanus Ward, 1917. Our results are consistent with the conventional systematics that places the four genera (Crepidostomum, Bunodera, Megalogonia and Allocreadium) within the same family.
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