Genetic variation in the planktonic chaetognaths Parasagitta elegans and Eukrohnia hamata

Two species of planktonic chaetognaths, Parasagitta elegans (Verrill) and Eukrohnia hamata (Mobius), from waters off Japan were analyzed electrophoretically and found to display very low levels of genetic variabhty. Nineteen enzyme loci were examined for 7 population samples of P, elegans, and the proportion of polymorphic loci (P,,,,) and average frequency of heterozygotes per locus ( H ) were calculated as 0.11 and 0.026, respectively. Fifteen enzyme loci were examined for 2 populations of E. hamata, and and H were calculated as 0.10 and 0.038, respectively. On the basis of allele frequencies at 2 enzyme loci it is possible to suggest that P. elegans population samples collected in the Sea of Japan were reproductively isolated from those in the Oyashio. Moreover it would appear that 4 population samples of P. elegans in the Sea of Japan are representative of a panmictic population. Differences in allele frequencies between population samples of the Oyashio suggest that these populations are genetically structured. It appears that genetic structuring exists in the 2 population samples investigated for E. hamata also. P. elegans and E. hamata expressed no common alleles over all the loci assayed indicating that the 2 species are phylogenetically very distant within the phylum Chaetognatha.