Annelids, like many other invertebrate animals, replace lost body parts in a process called regeneration. In particular, polychaetes, a class of generally marine annelid worms, are capable of regenerating to some degree. The degree of regeneration varies widely across the taxon. For instance, Pygospio elegans (Spionidae, Annelida) is capable of regenerating both head and tail segments, whereas Arenicola marina (Arenicolidae, Annelida) does not regenerate lost segments. The aim of the project is to assemble transcriptomes of two polychaetes - Pygospio elegans and Arenicola marina, - and to prepare data for further investigation of genes responsible for gradient expression in the body of annelids.