The Development of the Vermiform Embryos of Two Mesozoans, Dicyema acuticephalum and Dicyema japonicum

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The pattern of cell division and the cell lineage of the vermiform embryos of dicyemid mesozoans were studied under the light microscope using fixed and stained specimens of two species, namely, Dicyema acuticephalum, which has 16 to 18 peripheral cells, and Dicyema japonicum, which has 22 peripheral cells. An agamete first divides into two apparently equivalent daughter cells which remain in contact with one another. One of these cells becomes the mother cell of the head of the embryo. The other cell divides again equally to produce the prospective axial cell and the mother cell of the trunk and the tail of the embryo. The division proceeds spirally in the early stages but becomes bilateral from the fifth cell division onward. The embryo finally exhibits apparently bilateral symmetry. In two lines of cells, namely, those descended from the prospective axial cell and those from the mother cell of the head , extremely unequal divisions occur and the resultant, much smaller cells from each unequal division degenerate and ultimately disappear during embryogenesis. At the thirteen-cell stage, peripheral cells surround the prospective axial cell. At the final stage of embryogenesis, the prospective axial cell divides into two daughter cells . The anterior one is the axial cell itself and the posterior one is incorporated into the axial cell to form an agamete. Differences in numbers of peripheral cells are due to the number of times that divisions of the mother cells occur. The cell lineage of the calotte differs between D. acuticephalum and D. japonicum.
社団法人日本動物学会の論文
1994-04-15

The Development of the Vermiform Embryos of Two Mesozoans, Dicyema acuticephalum and Dicyema japonicum

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