Structural changes in olive ridley turtle eggshells during embryonic development

We examined the chemical composition and ultrastructure of the eggshells of olive ridley turtles, Lepidochelys olivacea , at various stages of embryonic development (freshly laid, 42 days developed and hatched). The eggshell is mainly composed of calcium carbonate present in its aragonite morph, and serves as a source of calcium for the developing embryo. Gradual utilization of eggshell calcium by the developing embryo was reflected by sequential reduction of calcium content from the fresh eggshell (191±32 mg), through 42 days into development (151±36 mg), to hatching (69±11 mg). Structurally, the shells of olive ridley turtle eggs were composed of an outer inorganic calcareous layer, an inner organic fibrous layer and a thin boundary layer that enclosed the egg contents. Calcium resorption by the developing embryo also brought about remarkable modifications in the structure of the eggshell. Fresh eggshells were composed of closely spaced, organized nodular shell units, disoriented spicules and a dense mat of membrane fibres. After 42 days of incubation, these nodules changed to polygonal units with large inter-spaces and loose fibrilliar membranes, whereas the hatched eggshell appeared amorphous and homogenous with disoriented membrane fibres. A 37% decrease in shell thickness (150±11 m in fresh to about 100±6 m in hatched) was observed between laying and hatching. This decrease in shell thickness and structural modifications, with respect to compositional changes, were the effect of calcium resorption from the eggshell by the embryo during its development.