Ultrastructural features and elemental distribution in eggshell during pre and post hatching periods in the green turtle, Chelonia mydas at Ras Al-Hadd, Oman

• Published in: Tissue & cell 2009-06, Vol.41 (3), p.214-221
• Main Authors: Al-Bahry, S.N, Mahmoud, I.Y, Al-Amri, I.S, Ba-Omar, T.A, Melgheit, K.O, Al-Kindi, A.Y
• Format: Article
• Language: English
• Subjects: Advanced Basic Science; Animals; Calcium - analysis; Calcium - chemistry; Calcium - metabolism; Calcium Carbonate - chemistry; Calcium Carbonate - metabolism; Chelonia mydas; Chorioallantoic Membrane - chemistry; Chorioallantoic Membrane - metabolism; Chorioallantoic Membrane - ultrastructure; Crystallography, X-Ray; Crystals; Eggshell; Elemental distribution and mapping; Elements; Female; Green turtles; Microscopy, Electron, Scanning; Sodium Chloride - chemistry; Sodium Chloride - metabolism; Spectrum Analysis; Temperature; Turtles - anatomy & histology; Turtles - physiology; Ultrastructure; Water - chemistry; Water - metabolism; Zygote - chemistry; Zygote - metabolism; Zygote - ultrastructure
• ISSN: 0040-8166; 1532-3072
• DOI: 10.1016/j.tice.2008.11.002

Abstract Eggshells were randomly collected from turtle nests immediately after oviposition and at the end of incubation to examine the ultrastructural features using scanning JSM-5600LV microscopy. Three layers were recognized; an outer calcareous, a middle multistrata and an inner membrane. The calcareous layer had loose nodular units varying in shape and size without interlocking attachments. In freshly laid eggs, each nodular unit had spicules arranged in folded stacks. The spicules became unfolded during incubation, to form radiating configurations. Elemental composition and mapping of the layers were analyzed using energy dispersive spectroscopy (EDS). The elements were unevenly distributed throughout the eggshell and Ca2+ decreased significantly after hatching. X-ray diffraction was used to identify the crystals of the eggshells. It revealed that nodular units of the calcareous were made up of CaCO3 , as aragonite (91%), calcite (6%) and vaterite (3%). The middle layer consisted of organic amorphous material with aragonite (89%) and calcite (11%). The shell membrane consisted of reticular fibers with crystals predominantly of NaCl halite. Thermogravimetry analysis of the calcareous layer indicated a complete evaporation of bonded H2 O at 480 °C and CO2 at 830 °C. Using the differential thermal analysis (DTA), aragonite was transformed to stable calcite at 425 °C.