Quantitative karyotype of Choromytilus chorus (Mollusca: Bivalvia: Mytilidae)

Chromosomes of the mussel Choromytilus chorus were studied using mitotic metaphase plates from early embryos. The diploid chromosome number was 2n = 30, and the karyotype showed metacentric and submetacentric chromosomes. Heteromorphic pairs and the nucleolar organizer region (NOR) were not observed clearly. The karyotype of this species differs from those of other species of Mytilidae in chromosome number and chromosome morphology of metacentric and submetacentric chromosomes, and absence of subtelocentric chromosomes.