It has been recently shown that P. omphalodes sensu stricto is primarily a parasite of Microtus agrestis (L.) and M. arvalis (Pallas) in Europe and probably elsewhere in western Eurasia ( Haukisalmi et al. 2004). There is another, rather host-specific species in M. oeconomus (i.e. Paranoplocephala jarrelli Haukisalmi, Henttonen & Hardman, 2006) that occurs in the root/tundra vole throughout its Holarctic range. The P. omphalodes - like taxon occurring in the eastern Beringian endemic Microtus miurus Osgood is also specifically distinct (i.e. Paranoplocephala batzlii Haukisalmi, Henttonen & Hardman, 2006; see Haukisalmi et al. 2006).
The present molecular phylogenetic analysis shows unequivocally that the P. omphalodes -like cestodes in Buryatia do not represent the true P. omphalodes ( Fig. 1).
The Buryatian specimens form a monophyletic group that is sister to the divergent North Alaskan subclade of P. jarrelli. The topology and high statistical support of the tree suggests that these two clades are both independent species, forming a sister group for the true, Holarctic P. jarrelli.
In the present material, the Buryatian P. cf. omphalodes occurred exclusively in Microtus fortis and M. oeconomus. Paranoplocephala omphalodes has earlier been report- ed from M. maximowiczii, M. oeconomus, Myodes rufocanus and Apodemus peninsulae in Buryatia and adjacent regions ( Machul’skii 1958; Zhaltsanova 1992). The earlier Buryatian records of P. omphalodes from Myodes rufocanus probably represent another, recently described species (i.e. Paranoplocephala buryatiensis Haukisalmi, Hardman, Hardman, Laakkonen, Niemimaa & Henttonen, 2006; see below).
Paranoplocephala cf. omphalodes from Buryatia may be primarily associated with the Asian Microtus species, i.e. M. fortis and M. maximowiczii, because it is not known from M. oeconomus outside Buryatia. Paranoplocephala cf. omphalodes will be later described as a new species.
Paranoplocephala cf. omphalodes was present in seven of the 12 study sites, highest prevalences being 20-23% ( Table 1).
Voucher specimen: MSB Endo 153 from M. oeconomus (Nizhnaya Ivolga).