Ontogenetic change of distributional patterns of pore systems in Cythere species and its phylogenetic significance

Species of Cythere (Ostracoda, Crustacea) have about one hundred normal pore systems on each valve of the carapace. These can be classified into five types on the basis of morphological features. They were examined in the light of intraspecific variation and interspecific difference. Each of the five pore systems has its own mode of ontogenetic increase in number. Comparison among fourteen Cythere species shows that the distributional patterns are completely identical in the A-3 stage, but that they are classified into four and eight groups in the A-2 and A-1 stages, respectively. In the adult stage the pattern becomes diversified among the fourteen species, though homologous relationships are still recognized between different species. The similarity and difference of the pore patterns, which are traceable until the last ontogenetic stage, can be used to determine phylogenetic relationships. These findings were applied to the reconstruction of phylogeny of the eleven living and three extinct species of Cythere. □ Crustacea. Ostracoda , Cythere, Ontogeny. Phylogeny, pore system, pore canal. speciation, laroal morphology.