日本産 Glossaulax (Gastropoda : Naticidae) の進化 : 第一部 : G. didyma, G. vesicalis, G. bicolor および G. reiniana の進化

抄録

Japanese Glossaulax ranges in age from the Middle Miocene to Recent, and consists of the following seven species : G. didyma (Roding), early Middle Miocene-Recent; G. vesicalis (Philippi), Early Pleistocene-Recent; G. hyugensis (Shuto), Early Pliocene-Late Pliocene; G. hagenoshitensis (Shuto), Late Pliocene-Early Pleistocene; G. nodai Majima, Late Pliocene-Early Pleistocene; G. bicolor (Philippi), Late Miocene-Recent; and G. reiniana (Dunker), Late Pliocene-Recent. Among them, the evolution of G. hyugensis, G. hagenoshitensis and G. nodai is discussed in part II of the present study. Glossaulax didyma is considered to be a descendant of a Glossaulax species in northwestern America where Glossaulax ranges in age from the Eocene to Recent. In Pliocene time, G. didyma gradually changed its morphology and increased its morphological variability. Glossaulax vesicalis evolved from G. didyma. In Late Pliocene time, G. didyma had a local population that showed an extremely wide range of morphological variation, including one variant very similar to the earliest known individuals of G. vesicalis. This population appears to be a transitional population between G. didyma and G. vesicalis. Glossaulax bicolor and G. reiniana are considered to be descendants of G. didyma. They share some important characters with G. didyma.