Ultrastructural and physicochemical characterization of egg shells in Pomacea canaliculata.

CATALÁN M; BABOT E; FERNÁNDEZ S; WINIK B

Córdoba, Argentina

Congreso; XI Argentine Congress of Morphological Sciences. First Intemational Congress of Education and Research in Morphological Sciences. First Meeting of Histotechnology.; 2008

Sociedad Chilena de Anatomía

ULTRASTRUCTURAL AND PHYSICO-CHEMICAL CHARACTERIZATION OF EGG SHELLS IN Pomacea canaliculata (GASTROPODA, PROSOBRANCHIA). Marta Catalán, Esteban Babot, Silvia Fernández, Beatriz Winik Facultad Ciencias Naturales e IML. Universidad Nacional de Tucumán. Argentina. Ampullarids are amphibian gastropods with different modalities in egg laying. Some lay their eggs in the water and form eggs embedded in a jelly-like mass while others, such as Pomacea canaliculata, lay calcareous-shelled eggs above water level. The objective of this work is to determine the physico-chemical and ultrastructural characteristics of the egg shells of this species. The egg shell ultrastructure was studied by processing freshly laid eggs with the routine techique for transmission electrón microscopy (TEM). The calcium material in the egg shells was studied with scanning electrón microscopy (SEM) and its chemical nature and crystalline polytype were determined through X-ray difractometry (XRD). The egg shell exhibits a multilayer organization. It has strongly mineralized electron-dense layers alternating with electron-lucid non calcified ones. XRD shows that the egg shell is formed by high crystalline vaterite. SEM shows the cryptocrystalline appearance of the vaterite. On the outside, the egg shell has a mucous envelope of low electrón density with small electron-dense microfibrils. ■The laying of above water level eggs with a calcified shell would protect the embrryo against drying. • The layer organization would confer hardness and resistance to the egg shell. • The layer´s calcificaron would indícate the acidic nature of the organic substrate and determine its electrón density. • The instability of the vaterite would favor the movement of calcium from the pallial oviduct stores to the lumen to form the egg shell and from the egg shell to the embryo. • The high crystallinity of the vaterite would confer greater strength to the egg shell and contribute to its structural support. • The outer mucous envelope of the eggs would have an adhesive function.