Owenia fusiformis is an ancestral sister group to the annelids, it has a unique "head larvae" type named mitraria larvae. To identify the gene expressed in different tissues, especially the gene expressed in head region, we dissected the 5 female worms and 1 male worm to get 9 different tissues, and extracted their RNA. The sequencing were performed on BGISEQ-500 platform, and the mapping were done with Kallisto and normalization was performed with DEseq2. Overall design: We dissected 5 female worms to get the head and tail tissues 1 female worm to get the gut, muscle and overy tussues 1 male worm to get the cheate, testis, blood vessel and muscle tissues.