Systematization and description of composition and structure of the monogeneans from the genus Dactylogyrus Diesing, 1850 mostly having five rayed ventral (additional) bar of the haptor and parasitizing mainly Palaearctic Barbinae and Leuciscinae, were carried out. These dactylogyrids have Palaearctic origin and occur in the north-western Africa, central and southern Europe, Transcaucasia, middle Asia, Mesopotamia and also in India and the Malacca Peninsula. Previously the analysis of dactylogyrids' distribution by continents (Gerasev et al., 1996), geographical regions (Gerasev, Timofeeva, 1997), taxonomic groups of hosts (Gerasev, 2008a, 6), and different taxonomic groups of host inside one geographical division (Kolpakov et al., 2007; Gerasev et al., 2007, 2008) was performed. This analysis have not been always resulted in the understanding of conjugate evolution of these parasites and their fish hosts, as well as in the resolving of problems concerned with speciation of monogeneans and phylogeography of their hosts. Therefore, in present work we consider more than one geographical region, different fish taxa, and the morphological groups of worms reflecting morphological variational series of types of copulatory organ and additional bar. Typification of copulatory organ, additional bar, anchors, and type of seating for 11 Palaearctic morphological groups of dactylogyrids mainly having five rayed additional ventral bar, were carried out. Four morphological groups of dactylogyrids of African, Indian, and different Palaearctic origin also parasitizing Palaearctic barbs were additionally included into analysis. In all, 92 species of dctylogyrids from 78 host species were considered. Analysis of speciation and phylogeny of dactylogyrids having five rayed additional ventral bar of haptor; conjugate evolution of these dactylogyrids and their fish hosts (mainly Barbinae); point of origin of Palaearctic polyploids Barbinae, and expansion of these fishes over the territory of Palaearctic will be discussed in next article.