The sea urchin Echinometra mathaei (Blainville) which belongs to the order Echinoida, occurs in abundance on shallow reefs throughout the tropical to warm Indo-Pacific region. Though Okinawan E. mathaei had been considered as a single species showing extensive morphological variation in test shape and spine colour, it was recently shown that the genus Echinomtra consists of four independent species (Uehara & Shingaki, 1984, 1985; Arakaki et al., 1998). However, the scientific names of these four complex species found in Okinawa are still unclear. These Echinometra are tentatively described here as Echinometra sp. A, B, C and D. Echinometra sp. A is characterised by white-tipped spines, a definite bright milled ring and dark skin on the peristome. Echinometra sp. B is characterised by spines with no white tip, with very faded milled rings and dark skin on the peristome. Echinometra sp. D is characterised by spines without a white tip but with a definite bright milled ring and bright skin on the peristome. In the field, these two Echinometra sp. exhibit a richly coloured variation in spines. Echinometra sp. D is characterised by deep black spines with well-defined milled rings and dark skin around the peristome. Only black-spined individuals have been found so far. In addition, these species show different distribution patterns, habitat preference and agonistic behaviour. It has also been shown that these two species are not possible to cross-fertilise under sperm at limiting concentration.