陆栖肺螺类壳质超微结构的研究及其与半咸水螺壳的对比

STUDIES ON SHELL ULTRASTRUCTURE OF LAND SNAILS IN CONTRAST WITH BRACKISH WATER SNAILS

有关海相腹足类壳质超微结构的研究已有不少报道,而对非海相腹足类,尤其是陆栖肺螺类的壳质超微结构研究仍然非常少见。因此,本文拟通过一些陆栖肺螺壳和半咸水螺壳的壳质超微结构的研究,建立其壳质超微结构的类型,并对比这两大类群的螺壳在壳质超微结构上的区别。

This paper illuminates eight types of shell ultrastructure in nonmarine Gastropoda, namely, irregular simple-prismatic, fibrous-prismatic, fibrous-needle, crossed lamellar, crossed needle, cone complex crossed lamellar, plate and myostracal layer, among which the plate structure is a new type discovered only in Palaeostrobilops. This paper also disousses some interesting problems concerning the shell ultrastructure. As to the differences between the uhrastructure of Mesogastropoda (brackish water snails) andthat of Stylommatophora (land snails), five aspects can be considered: 1. In the type of shell structure, the plate structure appears only in Stylommatophora; 2. In the arrangement and combination of the shell layer, the regularity of several crossed lamellar layers overlapping each other generally involves the concentric crossed lamellar layer and the radial crossed lamellar layer from outside to inside in Stylommatophora, but it is just the opposite in Mesogastropoda; 3. In the uhrastructural character of the inner most layer, the fibrous-needle type generally constructs the inner most layer of Mesogastropoda, but the fibrous-prismatic type generally constructs that of Stylommatophora; 4. Judged from the difference of shell ultrastructure in the position of whorl, the crossed needle layer appears mainly in the inner shell layer in the early stage of the whorl in Mesogastropoda, but it appears in the middle layer near the aperture in Stylommatophora; 5. In the nuclear ultrastructure, it is composed of fibrous-needle layer and crossed lamellar layer in Mesogastropoda, but it is also intercalated with a myostracal layer in addition to the fibrous-prismatic and crossed lamellar types in Stylommatophora.