Order Echinoida in Japan is now classified into the following five families: Temnopleuridae, Toxo-pneustidae, Strongylocentrotidae, Echinometridae and Parasaleniidae. With the exception of the Parasaleniidae, four of the families are commonly found in shallow waters in Japan. Interrelationships among these four families have been extensively studied by many workers using morphological criteria or at the biochemical and molecular levels, and four different theories have been proposed (Jensen, 1981; Smith, 1984; Mortensen, 1928–1951; Shigei, 1986; Matsuoka, 1988). To examine these theories, I attempted to obtain hybrids using 14 species (4 species of the family Temnopleuridae: Temnopleurus toreumaticus, Temnopleurus hardwickii, Temnopleurus reeversii and Mespilia globulus; 3 species of the family Toxopneustidae: Toxopneustes pileolus, Tripneustes gratilla and Pseudoboletia maculata; 4 species of the family Strongylocentrotidae: Strongylocentrotus intermedius, Strongylocentrotus nudus, Hemicentrotus pulcherrimus and Pseudocentrotus depressus; and 3 species of the family Echinometridae: Anthocidaris crassispina, Echinostrephus aciculatus and Echinometra mathaei).