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Still alive? Fine structure of the barrels made by Phronima (Crustacea: Amphipoda)

Published online by Cambridge University Press:  09 November 2005

Euichi Hirose
Department of Chemistry, Biology, and Marine Science, Faculty of Science, University of the Ryukyus, Okinawa 903-0213, Japan
Masakazu N. Aoki
Shimoda Marine Research Center, University of Tsukuba, Shimoda, Shizuoka 415-0025, Japan
Jun Nishikawa
Ocean Research Institute, The University of Tokyo, Nakano, Tokyo 164-8639, Japan


Amphipods of the genus Phronima are known to make a barrel-shaped house from the gelatinous matrix of pelagic tunicates or siphonophores. Among the seven barrels examined here, one barrel of Phronima curvipes was supposed to be made from a swimming bell of a siphonophore based on its morphology, while the other six barrels made by P. sedentaria were immunochemically and/or morphologically identified as tunicates (i.e. Thetys vagina, other salps and pyrosomas). Histological observation showed that the phronimids had completely eaten the animal tissues other than the gelatinous matrix (i.e. tunic or mesoglea). Tunic cells were found in the tunicate barrel and some were probably tunic phagocytes that appeared to be alive and functional. In the tunicate barrels, cuticular layers of the tunic were found on both the outer and inner side of the barrel wall. Tunic cuticle would be regenerated on the inner side after the epidermis was grazed by the phronimids. The cuticular layers would protect the tunic matrix from the invasion of microorganisms. In the barrel supposed to originate from Thetys vagina, there are minute protrusions on the tunic cuticle as found in the intact tunic of this species. In the barrel from a siphonophore, neither cells nor cuticle regeneration were found. No bacteria were observed in the barrel, suggesting that the barrel has some antibiotic system.

Research Article
© 2005 Marine Biological Association of the United Kingdom

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