The Development of Two Species of Tetilla (Demosponge)
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概要
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1. The fertilization and development of two species of oviparous sponges, Tetilla serica and Tetilla japonica, were described. The results of this study show that these two species have common features in their development, but this is very unusual as compared with that of other sponges. 2. The mature egg is released through the maternal osculum and fertilized outside the body. After fertilization, it immediately adheres to the substratum without a free-swimming larval period and develops directly ; this is not observed in other sponges. 3. These species have radiating fiber bundle on the egg surface, which are taken into the perivitelline space after fertilization. At this time the egg performs a sepcial type of rotation which is not known in any other eggs. 4. The radiating fiber bundles taken into the perivitelline space and the space itself will be incorporated into the larva as the development proceeds. This accessory covering of the egg is imagined to be the structure which carries substance to the larva from the maternal body, as has observed in other sponges. 5. The larvae of two species of Tetilla do not differentiate the columnar flagellated cell layer, characteristic of parenchymella larva, but differentiate directly adult ectosome and choanosome from undifferentiated cells of morula. 6. When the larva forms an aquiferous system and skeleton and develops to be a rhagon larva, alternation of body symmetry is seen in T. serica, not in T. japonica. 7. At present stage of study, the development of Tetilla seems very unique among the sponges, but with the progress of research on oviparous sponges, the relation within the Demosponges or the phylogenetic position in the Porifera of these species may possibly have to be reconsidered.
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