AbstractThe widely distributed Brachionus calyciflorus was studied for morphological variation based on material from all tropical areas. The subspecies B. calyciflorus borgerti Apstein is redescribed and its subspecific status affirmed. Various forms with local distributions were noted and described and the morphological differences are attributed to a variety of possible factors. From the distribution patterns it is clear that rotifers are governed by the general principles that apply to other invertebrates and are not cosmopolitan. There are evidently dispersal centres for Brachionus calyciflorus and its subspecies borgerti.