The DNA of the Antarctic scallop Adamussium colbecki was found to contain a highly repeated sequence identifiable upon restriction with endonuclease BglII. The monomeric unit - denominated pACS (about 170bp long) - was cloned. Southern blot hybridization yielded a ladder-like banding pattern, indicating that the repeated elements are tandemly arranged in the genome and therefore represent a sequence of satellite DNA. Sequence analysis of five different clones revealed the presence of various subfamilies, some of which showed a high degree of divergence. In each clone, regions homologous to the mammalian CENP-B box were observed. A region homologous to the CDEIII centromeric sequence of yeast was also found in one of the clones. These observations suggest a relationship of the pACS family to the centromeric area in A. colbecki.