Abstract
In this paper, molecular analyses of Baikal hydras from the ‘oligactis group’, based on COI and ITS1–5.8S–ITS2, and morphological analysis of their holotrichous isorhizas, were performed. Low genetic diversity and shared haplotypes were found between Hydra oligactis Pallas, 1766 and Hydra baikalensis Swarczewsky, 1923 specimens, which is evidence of the mixing of these lineages. Genetic distances among all Baikal hydras (0.006) were less than the interspecific distances of other hydras. The size of hydras and proportions of their holotrichous isorhizas varied depending on microhabitat and environmental conditions. Our combined molecular and morphological approach proves that H. baikalensis is synonymous with H. oligactis
Highlights
Hydra is a member of the ancient phylum Cnidaria, class Hydrozoa, order Hydroida, family Hydridae
The consensus tree topology based on c oxidase subunit I (COI) (27 unique haplotypes) indicated that Baikal H. oligactis and H. baikalensis did not form separate clades, but instead were clustered together with representatives of Hydra robusta Itô, 1947 from Japan and China and H. oligactis from Japan and Europe, forming a neighboring clade with the majority of hydras from Western Europe and North America (Fig. 1A)
Low genetic distance between the latter two species could be a consequence of shared ancestral polymorphism
Summary
Hydra is a member of the ancient phylum Cnidaria, class Hydrozoa, order Hydroida, family Hydridae. Freshwater representatives of Hydra inhabit virtually all zoogeographical regions except the Pacific Ocean Islands and Antarctica Peretolchina et al / ZooKeys 912: 1–12 (2020)
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