EVOLUTIONARY STUDY OF MARINE RELIC INVERTEBRATES

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(1) Ecological and taxonomic research : Kase, Hayami, Hanai, Tabuki, and Mori have found a peculiar primitive invertebrate faunas in the submarine caves in the tropical and subtropical Western Pacific. They collected many live and dead samples of the faunas and analyzed their ecological and taxonomic characteristic as a basis for future evolutionary researches.(2) Developmental biological research : Tanabe has investigated the mode of embryonic shell development in the primitive ectocochliate cephalopod Nautilus with the help of Mr. K.Uchiyama of the Toba Aquarium, and recognized a disks-shaped univalved organic shell (cicatrix) in the early stage. A similar shaped disk-shaped or low cap shaped primary shell is also known in extant Monoplacophora, suggesting their phylogenetic relationships.(3) Molecular systematic research : Endo, Ueshima, Ozawa, and Chiba have conducted DNA analysis of some primitive invertebrates such as brachiopods and stalked crinoids to establish their phylogenetic relationships at higher taxonomic levels.(4) Theoretical research : Chiba constructed numerical models to explain the log-term phenotypic-level evolution based on the theory of quantitative genetics.