棘皮動物の生活史の多様性とその系統分類学的意義(第6回日本動物分類学会賞受賞記念論文)
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概要
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Echinoderms display a great range of life histories, which my students, colleagues, and I have documented though our studies of 42 species, including one echinoid, one holothuroid, four ophiuroids, and 36 asteroids. Here, the general features of echinoderm reproduction are reviewed as they concern the following topics: pairing behavior, brooding, sexual dimorphism, dioecism/hermaphroditism, and others. Larval form in these echinoderms has been modified in various ways through adaptation to planktonic, benthic, intra-gonadal, or intra-gastric larval habitats. The elucidation by Kanatani of the hormonal control mechanism of reproduction in asteroids has provided a means to investigate various aspects of their life history in detail, especially in the genera Asterina, Astropecten, and Luidia. We have found asteroids that pass through a wrinkled blastula stage, divergences among species of Asterina and Astropectinidae, astropectinid sea stars with a newly discovered barrel-shaped larva, and the limits of occurrence of the non-brachiolarian type of development in the Astropectinidae and Luidiidae. The life history of astropectinid species, including both a bipinnaria and a barrel-shaped larva, differs from that of luiidiids, with only a bipinnaria. On this basis, we suggest that the Astropectinidae and Luidiidae probably do not belong to the same ordinal-level taxonomic group. This result agrees with the 18S rDNA-based asteroid phylogeny previously reported by Matsubara and us.
- 2009-08-20