The Ultrastructure of Chrysemys picta Eggshell and Shell Membrane

Abstract

The structure of eggshells plays a multifunctional role in successful embryogenesis. The avian eggshells have been extensively studied while there are few studies on reptilian eggshells. Painted turtle eggs exhibit pliable shells and have received attention by researchers because of its availability but general morphological characteristics of their eggshells have not been previously reported. The objective of the study is to describe the ultrastructure of the eggshell and shell membranes of preincubated and post incubated eggs of painted turtles (Chrysemys picta) using a Scanning Electron Microscope (SEM). Painted turtles lay oval-shaped, pliable-shelled eggs, eggshell is composed of outer calcareous layer and inner shell membrane. Outer mineral layer composed of loosely arranged shell units separated with pores traversing through the calciferous layer to the membrane. The size of shell units and pores increase with incubation suggests that the developing embryo derives calcium and water from the eggshell. The outer mineral layer is connected to the multilayered shell membrane at the basal knob. The outer shell membrane is composed of randomly arranged fibers organized into rough, filamentous meshwork and the inner membrane is in contact with the albumin consist of smooth, parallel arranged, featureless f ibers. In conclusion, eggs of painted turtle showed some similarities in morphology to other species of turtles that lay pliable-shelled eggs, the description on structural characteristics of an eggshell is essential to understand the chemical composition of the eggshell and its development.