| Summary: | 碩士 === 國立臺灣海洋大學 === 海洋生物研究所 === 99 === Embryonic development means the study of processes of morphological changes from the fertilized eggs to the hatchling. The studies of developmental processes enable not only the scientist to understand the embryogenesis pattern of different species but form the foundation of phylogeny study. At present, the studies of leech embryonic development were focused on freshwater leech, family Glossiphoniidae, but very few describe the marine leech Ozobranchidae. In this experiment, we used transparent fertilized eggs to understand the developmental pattern of marine leech Ozobranchus branchiatus and to compare with other leeches.
Under 25℃ seawater medium, the incubation period of Ozobranchus branchiatus lasted for 254 hours. According to the egg’s morphological characters, we separated the developmental processes into 11 stages and compared with other leeches. The study results found that, early developmental pattern was similar to Acanthobdella, but not Glossiphoniidae or Hirudinidae. Besides, the early embryogenesis of O. branchiatus was maintained the characters of ancient ciltellates, like typical three cell stage. In the middle embryonic development stages, the germinal band fused in the embryonic middle line and formation the germinal plate, then segmentation. During segmentation, the germinal plate moved slowly to ventral middle line. In contrast, the germinal band of Glossiphoniid and Hirudinidae was fused directly in ventral middle line, follow by the segmentation. We proposed that O. branchiatus has no ability to swim, but is able to crawl on seabed and infects the sea turtle when they rest on seabed. The migration behavior of sea turtle also allow them to be distributed wide range of geographic areas. Finally, the O. branchiatus found in this study is also the first record in Southeast Asia and Taiwan.
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