Development and budding in the oozooids of Polyclinum aurantium (a colonial ascidian) (Protochordata)


  • Mitsuaki Nakauchi

    1. Department of Biology, Faculty of Science, Kochi University, Asakura, Kochi 780, Japan
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    • The research was carried out at the Dunstaffnage Marine Research Laboratory of the Scottish Marine Biological Association.

  • This work was supported by an International Exchange Research Scholarship from the Ministry of Education of Japan.


The life history of oozooids of a polyclinid ascidian, Polyclinum aurantium was studied by rearing them in small tanks. A newly metamorphosed zooid has four rows of stigmata, and lacks a postabdomen. Three (or four) new stigmatal rows are added to the original ones during oozooid growth; this phenomenon is exceptional in polyclinid ascidians. The post-abdomen appears about 20 days after metamorphosis and grows rapidly. Budding occurs 40-70 days after metamorphosis. Buds of three kinds are formed: one thoracic bud (“mother zooid”), one abdominal bud, and five to eight postabdominal buds. Both in formation of new stigmatal rows in the oozooid and in the mode of budding, Polyclinum and Sidneioides are alike, and they are different from other polyclinids. Budding in ascidinas is discussed from the viewpoint of its biological significance.,