ABSTRACT
Echinometra mathaei is one of the most conspicuous animals on Okinawan coral reefs. This sea urchin is found abundantly in the intertidal rock pools, moats, and other subtidal habitats. More than twenty years ago, Dr Nishihira, an experienced field ecologist, noticed some subtle but distinct differences in the population of Okinawan Echinometra: E. mathaei seemed to be divided into subgroups according to their coloration, habitat, and behavior. Dr Nishihira and Dr Uehara, an developmental biologist, and their colleagues have extensively studied on this topic recently. Their conclusion is Okinawan E. mathaei is a complex of four species that are closely related but definitely different. The E. mathaei complex raises number of interesting questions to be answered and it provides an excellent system for the study of speciation in marine organisms living sympatrically.
