モクズガニのEpicaridizationについて
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概要
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About one-third of more than 1, 000 specimens of the fresh-water crab, Eriocheir japonicus collected in the River of Asahi, Okayama City, were parasitized by the entoniscid, Entionella fluviatilis. The results of studies of these specimens have been compared with the data of the same crabs bearing the entoniscid from the River of Yura, Tango Province, reported by Miyashita ('33; '35; '41). The effects of epicaridization upon female hosts are almost identical in both the collections, i. e., the female sexual characters remain in an undeveloped condition. In males, however, there are remarkable differences between the two. As is shown in Fig. 3, we can see local differences in sexual characters between the two collections even for normal crabs. The differences in parasitized crabs are much more remarkable than in the normal ones. In the River of Asahi, nearly all the parasitized male Eriocheir have transformed into intersexual conditions, showing the broadening of the abdomen and the loss of the bridge at the base of the copulatory styles. The findings are not comparable with those from the Yura specimens. Furthermore, in four extreme cases, one pair of female biramous pleopods are found (Fig. 2) The modifications of male abdomen produced by epicaridization become noticeable when the animal reaches the stage of 15mm carapace length. At that time the parasite attains the sexual moturity. The parasite, Entionella, seems to enter into the body of Eriocheir at the stage earlier than 6mm carapace length, because in this stage the parasite has developed far beyond the asticot form. The internal organs of the host are affected to varying degrees by the parasite which occupies a greater part of the haemocoel of the host from the very early stages of development. The liver becomes smaller, and the gonad is not found both in young and old specimens. The thoracic ganglion is often deformed probably by the pressure exerted by the parasite. Moreover, the histological study of the ganglion reveals the decrease of the nerve cells and the changes of their destribution (Fig. 7).
- 1953-10-15
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