Chapaev3-1_PM belongs to the Chapaev3 group of the Chapaev superfamily of DNA transposons. Chapaev3 transposons are present in animal genomes, including mammals (Chapaev3-1_ET in the Echinops telfairi hedgehog tenrec), reptiles (Chapaev3-1_AC and Chapaev3-2_AC in the Anolis carolinensis lizard), fish (Chapaev3-1_OL in the Oryzias latipes medaka), jawless vertebrates (Chapaev3-1_PM and Chapaev3-2_PM in the Petromyzon marinus lamprey), insects (Chapaev3-1_AA, Chapaev3-2_AA, and Chapaev3-3_AA in the mosquito Aedes aegypti; Chapaev3-1_DA and Chapaev3-1_DW from Drosophila ananassae and D. willistoni; Chapaev3-1_NVi in the parasitoid wasp Nasonia vitripennis); annelids (Chapaev3-1_HR, Chapaev3-2_HR, Chapaev3-3_HR and Chapaev3-4_HR from the leech Helobdella robusta), flatworms (Chapaev3-1_SM in the planarian Schmidtea mediterranea), and cnidarians (Chapaev3-1_HM, Chapaev3-2_HM, Chapaev3-3_HM in Hydra magnipapillata). Unlike 4-bp target site duplications introduced by canonical Chapaev transposons, members of the Chapaev3 group generate 3-bp TSDs upon their insertion in a host genome (usually TWA). Chapaev3 transposases are composed from the N-terminal ~105-aa Chapa zinc finger and a 260-aa Chapaev-like D-x54-D-x198-E catalytic core. All known Chapaev3 transposons have invariant 5'-CAC and GTG-3' termini. In terms of identities between their transposase protein sequences, Chapaev3 transposons form a very compact cluster, when the average identity is ~50%, which is higer than in other metazoan transposons. Also, the identities between TPases of Chapaev3 transposons do not follow a phylogenetic tree of their host species. Presumably, most of the Chapaev3 transposons have evolved through horizontal transfer between distant species in a "big bang"-like scenario. For instance, the hydra Chapaev3-1_HM and planarian Chapaev3-1_SM transposases are 70% identical to each other; the hydra Chapaev3-2_HM and leech Chapaev3-3_HR transposases are 63% identical to each other. The most clear example of a horizontal transfer role includes the tenrec Chapaev3-1_ET and lizard Chapaev3-3N1_AC families. In both genomes, the Chapaev3 transposons have lost their mobility more than a fiew million years ago: Chapaev3-1_ET elements are ~87% identical to their consensus sequence, and Chapaev3-3N1_AC elements are 80-90% identical the Chapaev3-3N1_AC consensus. At the same time, the Chapaev3-1_ET and Chapaev3-3N1_AC consensus sequences are 97% identical to each other! While the tenrec genome contains a few hundred copies of Chapaev3-1_ET (mostly non-autonomous elements), the lizard genome contains a few thousand copies of Chapaev3-3N1_AC (only a few copies of an autonomous transposon that are ~87% identical to the Chapaev3-1_ET consensus). In accordance with horizontal transfer of Chapaev3 transposons in tenrec and lizard (some 20-50 million years ago), Chapaev3 transposons are not present in genomes of other mammals (primates, rodents, dog, cow, marsupials, platypus). Chapaev3-1_PM is a young family of lamprey Chapaev3 transposons: genomic copies of Chapae3-1_PM elements are ~95% identical to their consensus sequence, which was derived from multiple alignment of 20 Chapaev3-1_PM elements. Chapaev3-1_PM contains 140-bp terminal inverted repeats. The 562-aa Chapaev3-1_PM transposase is encoded by two exons (in most Chapaev3 transposons the TPases is encoded by one ORF).