797. INTRASPECIFIC VARIATION IN THREE SPECIES OF GLOSSAULAX (GASTROPODA : NATICIDAE) FROM THE LATE CENOZOIC STRATA IN CENTRAL AND SOUTHWEST JAPAN

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  • 797. 西南日本後期新生代層産の Glossaulax (ツメタガイ属) (腹足綱 : タマガイ科)の 3 種の種内変異
  • 西南日本後期新生代層産のGlossaulax(ツメタガイ属)(腹足綱:タマガイ科)に3種の種内変異〔英文〕
  • セイナン ニホン コウキ シンセイダイソウサン ノ Glossaulax ツメ

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Abstract

The intraspecific variation within three Glossaulax species, G. hyugensis (Shuto), G. nodai, n. sp. and G. hagenoshitensis (Shuto), which had flourished in the late Cenozoic waters of Japan, was studied on the basis of more than 600 individuals collected from 24 localities. The three species overlap stratigraphically and geographically, and are distinguished from other Glossaulax species by having a nearly flat umbilical wall and a spiral angulation dividing the base and the umbilical wall. "Dimorphic" variation is recognized in the callus morphology of the adults of G. hyugensis and G. hagenoshitensis. One adult variant of G. hyugensis is similar to that of G. hagenoshitensis, and the other adult variant of the former species is similar to that of the latter, whereas the frequency of the similar adult variants of the two species is extremely different. G. nodai, however, is uniform in callus morphology throughout growth. In the callus morphology, the juvenile of G. hyugensis and that of G. hagenoshitensis are similar to G. nodai, and to one form of the adult "dimorphic" variation of G. hyugensis, respectively. Furthermore, G. hagenoshitensis is divisible into two allopatric forms in the sculpture of subsutural area and of umbilical wall margin. The mode of the ontogenetic variations of the three species is explained by a heterochronic model in which an imaginary ancestral species is presumed. G. hagenoshitensis has been taxonomically confused with Polinices sagamiensis Pilsbry and Glossaulax reiniana (Dunker), but is clearly distinguished from these two species on the basis of umbilical morphology.

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