Permalink :  http://hdl.handle.net/2115/36704

Organic components of typical prismatic layers in several molluscan shells were reexamined by applying scanning electron microscopy to preparations treated with the freeze-dry or the critical-point-dry method, with the result showing the following: The interior of prisms is almost filled up with a spongy intraprismatic matrix. Also three principal types of prisms are distinguishable according to the state of development and the histochemical nature of a vertical (interprismatic) wall. Namely, prisms of type 1 are separated from their neighbor by a rigid vertical wall, and are represented by calcite simple prisms of Pinctada and aragonite simple prisms of Anodonta: prisms of type 2 are separated by a compound (partly rigid and partly spongy) vertical wall, and are represented by aragonite simple prisms of Unio; prisms of type 3 are separated by a spongy vertical wall, and are represented by composite prisms of Tapes and Peronidia. These findings suggest that type 2 is intermediate between types 1 and 3, and that transformation of an interprismatic matrix from a "primitive" rigid matrix to a more "advanced" spongy one has probably taken place in the course of evolution of prisms. In addition, the histochemical nature of the rigid matrix is acidophilic like the shell epidermis. Meanwhile, the spongy matrix, regardless of being inter- or intraprismatic, is basophilic, and will have some connections with mineralization of prisms.

FULL TEXT :  PDF