Development of the First Vertebra in Oryzias latipes and its Morphology in Beloniformes and Cyprinodontiformes

概要

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To examine morphological characteristics usable in classification of Beloniformes and Cyprinodontiformes, the first vertebrae of many specimens were compared anatomically. Development of the first vertebra in Oryzias latipes was observed first to provide an understanding of its morphology and articulation with the skull. The first vertebra of adult O. latipes consists of the centrum, condyles for exoccipitals, neural arches with parapophyses, a neural spine and a small dorsal compartment in the neural canal. Next, the morphology of the first vertebrae in Beloniformes and Cyprinodontiformes was examined. The first vertebra in Beloniformes was composed of the same components as in O. latipes, but there were morphological modifications in the components in the Cyprinodontiformes. The present observations suggest that the lower position of the parapophyses in neural arches is a common feature of the first vertebra in Beloniformes.