Hox genes are the key regulators of axial regionalization of bilaterian animals. However, their main function can be fulfilled differently in the development of animals from different evolutionary branches. Early patterning of the developing embryos by Hox gene expression in the representatives of protostomes (arthropods, mollusks) starts in the ectodermal cells. On the contrary, the instructive role of the mesoderm in the axial patterning was demonstrated for some deuterostomian animals (vertebrates, echinoderms). This makes it more difficult to understand the ancestral state of axial regionalization. To resolve this question, it is necessary to expand the number of models for investigation of the early axial patterning. Here we show that three Hox genes of the polychaete A. virens (Annelidae, Lophotrochozoa) — Hox2, Hox4 and Lox5, are expressed in the mesoderm anlagen of the three future larval chaetigerous segments in spatially and temporally colinear manner before the initiation of Hox expression in the l