2005 Fiscal Year Final Research Report Summary
Natural historical study on the heteromorphic polyps distributed on the periphery of colonies of Cytaeis uchidae Rees, 1962 (Hydrozoa; Cytaeidae) from Japan
| Project/Area Number |
16570087
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Biodiversity/Systematics
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| Research Institution | National Museum of Nature and Science, Tokyo |
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Principal Investigator |
NAMIKAWA Hiroshi National Museum of Nature and Science, Tokyo, Tsukuba Research Center, Senior curator (40249909)
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| Project Period (FY) |
2004 – 2005
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| Keywords | hydrozoa / Cytaeis uchidae / heteromorphic polyps / positional specific differentiation |
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| Research Abstract |
This natural historical study aimed to reveal the characters of the heteromorphic polyps that discovered in the colonies of Cytaeis uchiudae Rees, 1962 (Hydrozoa; Cytaeidae) from Japan.
1. Heteromorphic polyps were found in fixed specimens collected from Sagami Bay (type locality) about 50 years ago, as well as in living colonies collected recently from Sagami Bay and Asamushi, Mutsu Bay (ca. 600Km distant from the former) and so on. Clearly, the morphological variations found have not resulted from environmental influences, as heteromorphic polyps occurred widely in colonies, regardless of the age of their host gastropods. Therefore, heteromorphic polyps must be considered as having some special function.
2. The heteromorphic polyps were characterized by 1) the presence of highly elastic tentacles armed with huge nematocysts of basitrichous isorhizas, and 2) a distribution confined to that part of the colony which bordered the periphery of the aperture of the gastropod host Niotha livescens (Phillippi). The basitrichous isorhizas were also observed in hydrorhizas distributed only along the aperture of the host Furthermore, these nematocysts were observed being transferred from the hydrorhizas to the normal polyps. It was clarified that the heteromorphic polyps were modified from the normal polyps as a result of the ingression of basitrichous isorhizas.
3. Possibly, the occurrence of huge nematocysts in the highly elastic tentacles also has a defensive function against potential competitors.
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