腹足類(リュウテンサザエ科)の石灰化蓋の構築構造

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The internal structure and mineralogy of the calcined opercula of five species of turbinid gastropods have been studied. The operculum consists of the inner organic and the outer calcified layers; the latter contains a small amount of organic matrix. In all species examined, the calcified layer has a shell microstructure of composite prismatic type. This microstructure is composed principally of acicular to thin prismatic aragonite crystals of about 0.1 to 1 μm in diameter, such componental crystals being aggregated to form a larger unit of the structure. The composite prismatic structure of the turbinid operculum is much more variable in form, size and branching manner of the aggregation of acicular crystals than that of the bivalvian shell. Furthermore, this microstructure of the operculum occasionally tends to change in structure by excessive enlargement in diameter of the componental crystals and has a structural similarity to an irregular prismatic type of the molluscan shell. Observations of such structural change indicate that the proportion of crystal nucleation and growth of the normal composite prismatic type may be strictly controlled by a physiological condition, for example, density of the secretion fluid, of the animal. In many individuals regardless of the species, small patches composed of a calcite blocky structure are present within the aragonite composite prismatic region. Judging from the internal thin bands (growth structure) of the patches and contact relation with the neighboring aragonite prisms, the calcite patches may initially be formed together with the surrouding aragonite parts. This occurrence may indicate that there is no obvious difference on the depositional conditions between aragonite and calcite in biological systems.
地学団体研究会の論文
1987-01-25

腹足類(リュウテンサザエ科)の石灰化蓋の構築構造

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