Abstract
Four morphospecies of foraminifera, Glabratella opercularis, G. subopercularis, G. nakamurai, and G. patelliformis, all of which have similar test morphologies, were reclassified by the use of both morphological characters and interbreeding experiments. Because specimens of Glabratella have been shown to reproduce sexually, it should be possible to determine breeding populational boundaries within Glabratella and to compare these with morphologically based taxonomic boundaries. Using stable characters, three morphogroups were reclassified from the four morphospecies. Laboratory interbreeding experiments revealed that individuals belonging to the same morphogroup formed gamontogamous pairs and then reproduced. However, individuals belonging to different morphogroups did not produce any gamontogamous pairs. This indicates that each of the reclassified morphogroups represents a distinct breeding population. Within the same morphogroup, individuals collected from two different localities closer than 100km apart could interbreed with each other. However, individuals from more than 500km apart could not breed with each other, even though the morphological characters of the individuals were very similar. This suggests that the population structure of the P. opercularis morphogroup is very similar to those of ring species.
