Electrophoretic Study on the Phylogenetic Relationships among Six Species of Sea-Urchins of the Family Echinometridae Found in the Japanese Waters : Systematics and Taxonomy

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The family Echinometridae of the order Echinoida found in the Japanese waters is represented by six sea-urchin species belonging to the five different genera. They are Anthocidaris crassispina, Echinometra mathaei. Echinostrephus aciculatus, Echinostrephus molaris, Heterocentrotus mammillatus and Colobocentrotus mertensii. The phylogenetic and evolutionary relationships among these six members of this family were investigated by electrophoretic analyses of 18 different enzymes. The biochemical dendrogram for the six species constructed from the Nei's genetic distances between species for 26 genetic loci showed the following: (1) H. mammillatus and C. mertensii are largely genetically differentiated from the other four species, and these two species are considered to be more primitive sea-urchins among echinometrids from the molecular estimation of their divergence time. (2) A. crassispina endemic to Japan is more closely related to Echinometra than to Echinostrephus, and it is estimated that Anthocidaris has speciated in relatively recent geological age of the late Pliocene. (3) The two morphologically very similar species of Echinostrephus (E. aciculatus and E. molaris) are little genetically differentiated from each other, and therefore these two may belong to one and the same species. These electrophoretic results are discussed through the detailed comparison with other molecular and non-molecular results.