The Yuriyagai: J. Malacozool. Ass. Yamaguchi, 9(1). August 2003

Original Articles

A taxonomic note on Mancinella siro (Kuroda) and M. echinata (Blainville) (Gastropoda: Muricidae)

Koh-Siang TAN

Abstract Although Mancinella siro (Kuroda) and M. echinata (Blainville) possess shells that are remarkably similar to each other, they have generally been regarded as separate species in Japan. Currently, however, there is little supporting evidence to substantiate their status as two distinct species. In this study, several morphological traits of the two species in addition to the gross morphology of the shell were examined to assess their taxonomic position. While shell microstructure, radula, penis morphology and gross anatomy of the two species appear to be virtually indistinguishable from each other, consistent differences in the morphology of the shell aperture and operculum suggest their separate taxonomic status.

Key words: Muricidae, Mancinella, taxonomy

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Arthritica japonica, sp. nov. (Bivalvia: Galeommatoidea: Leptonidae), a commensal with the pinnotherid crab Xenophthalmus pinnotheroides White, 1846


Abstract At two western Japanese tidal flats Arthritica japonica sp. nov. lives attached to the legs and carapace of the brachyuran crab Xenophthalmus pinnotheroides (family Pinnotheridae). This is the fourth example reported of a commensal bivalve associated with crabs. The species is a brooding and probably cross-breeding simultaneous hermaphrodite which may reproduce at a shell length of less than 2 mm. Contrary to other members of the family, the outer demibranch has been lost, presumably as a result of the species' small adult size. The sperm cells have very long and narrow corkscrew-shaped heads.

Key words: Arthritica japonica, Xenophthalmus pinnotheroides, anatomy, taxonomy, commensal, Brachyura, Japan

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Distribution patterns of assimineid species (Gastropoda: Rissooidea) in the salt marshes of the Yoshino River, Tokushima Prefecture, Japan

Miki KURODA, Keiji WADA, Mahito KAMADA, Kôhei SUZUKIDA and Hiroshi FUKUDA

Abstract The authors surveyed the spatial and vertical distributions of assimineid species in the salt marshes of the estuary of the Yoshino River, Tokushima Prefecture over a cycle of four seasons. Assiminea hiradoensis and As. japonica were widely distributed from the lower to upper parts of salt marshes in the lower to upper reaches, with their densities being high in the lower part of the salt marsh. Angustassiminea castanea was distributed in the lower reach and As. parasitologica in the middle to upper reach, and these two species also inhabited the middle parts of the salt marshes. Assiminea yoshidayukioi was restricted to the upper part of the salt marshes in the upper reach. Factors influencing the distribution patterns of the five species is discussed in terms of the salinity gradient, density of reeds, litter coverage, degree of drying and others. All species except As. yoshidayukioi were observed to climb reed stalks in summer, but this behavior was not often observed in winter.

Key words: Assiminea hiradoensis, Assiminea japonica, Assiminea parasitologica, Assiminea yoshidayukioi, Angustassiminea castanea, vertical distribution, spatial distribution, reed, salt marsh, estuaries

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