title: Ultrastructural features and elemental distribution in eggshell during pre and post hatching periods in the green turtle, Chelonia mydas at Ras Al-Hadd, Oman.
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 Ca(2+) 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 CaCO(3), 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 H(2)O at 480 degrees C and CO(2) at 830 degrees C. Using the differential thermal analysis (DTA), aragonite was transformed to stable calcite at 425 degrees C.
authors.affiliation: Department of Biology, College of Science, Sultan Qaboos University, P.C. 123, Al-Khodh, Oman. snbahry@squ.edu.om
authors.forename: S N
authors.initials: SN
authors.lastname: Al-Bahry
authors.forename: I Y
authors.initials: IY
authors.lastname: Mahmoud
authors.forename: I S
authors.initials: IS
authors.lastname: Al-Amri
authors.forename: T A
authors.initials: TA
authors.lastname: Ba-Omar
authors.forename: K O
authors.initials: KO
authors.lastname: Melgheit
authors.forename: A Y
authors.initials: AY
authors.lastname: Al-Kindi
mesh_terms: D000818:Animals; D002118:Calcium / Q000032:analysis / Q000737:chemistry / Q000378:metabolism; D002119:Calcium Carbonate / Q000737:chemistry / Q000378:metabolism; D049033:Chorioallantoic Membrane / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D018360:Crystallography, X-Ray; D004602:Elements; D005260:Female; D008855:Microscopy, Electron, Scanning; D012965:Sodium Chloride / Q000737:chemistry / Q000378:metabolism; D013057:Spectrum Analysis; D013696:Temperature; D014426:Turtles / Q000033:anatomy & histology* / Q000502:physiology; D014867:Water / Q000737:chemistry / Q000378:metabolism; D015053:Zygote / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D004602:Elements; D014867:Water; D012965:Sodium Chloride; D002119:Calcium Carbonate; D002118:Calcium