To investigate the roles of protein kinase C (PKC) isoforms in Echinoderms, we cloned starfish cDNAs for novel, atypical, and conventional PKCs. They showed highest homology with PKCdelta, iota, and alpha isoforms respectively. It was predicted from the whole genome sequence and by RT-PCR that sea urchin has only one isoform of each PKC subgroups. It is thus likely that these isoforms are the prototypes or ancestors of the PKC subgroups. The phylogenetic tree suggests that atypical PKC was first formed by evolution from the common prototype of AGC protein kinase family, and novel and conventional PKCs next. RT-PCR analysis indicated that novel and atypical PKC mRNAs are expressed ubiquitously in all tissues of adult starfish, whereas conventional PKC mRNA is expressed mainly in the ovary and oocytes, and only slightly in the tube foot and stomach. Upon heterologous expression, only atypical PKC was expressed in the functional form in insect cells.