| Budget Amount *help |
¥7,000,000 (Direct Cost: ¥7,000,000)
Fiscal Year 2000: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1999: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1998: ¥5,400,000 (Direct Cost: ¥5,400,000)
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| Research Abstract |
In this year I conducted two major researches in relation to this grant ; 1) SEM observation of the skeletal growth during developmental stages of three species of modern comatulids, 2) Fossil evidence about the presumable rapid evolutionary changes of the subclass Articulata across the Paleozoic-Mesozoic boundary.
Specimens of Oxycomanthus japonicus were collected from Koajiro Cove of Sagami Bay, and their spawning and development after fertilization were monitored. Also, pentacrinoid stage of two other comatulids, Antedon bifida and Decametra tigrina, were observed. The results include :
1. Anal plate was detected in pentacrioids of Oxycomanthus j. for the first time. This is the first report of anal plate from the suborder Oligophreatina. The anal plate were widely observed in the three subclasses of the Paleozoic, but this discovery from some articulata implies that its existence cannot be a good character of the articulata.
2. All three comatulids share synarthrial articulation in the pentacrinoid stalk. The present data, combined with previous data about pentacrinoids of various articulates, suggest that existence of synarthry in the pentacrinoid stalk would be a good synapomorphic character of the Articulata.
3. The number of columnals probably increases during the cystoid stage, but it is almost constant and longitudinal grow of each columnals are observed during the pentacrinoid stage.
Also data about Late Permian-Early Triassic articulates, both specimens (NE Japan, Nevada) and data from reference papers, shows the following :
4. Across the boundary, the number of ligamentary articulations in the arms suddenly decreased, and articulates have acquired the ability of arm autotomy at ligamentary acticulations. This evolutionary novelty must deeply be related to the suceess of the Articulata.
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