We report a unique shell margin that differed from the usual shell structure of Pinctada fucata.We observed empty organic envelopes in the prismatic layer and the formation of the nacreous layer in the shell margin.All the characteristics of the growing margin indicated that the shell was growing rapidly.To explain this anomaly,we propose the concept of "jumping development".During jumping development,the center of growth in the bivalve shell jumps forward over a short time interval when the position of the mantle changes.Jumping development explains the unusual structure of the anomalous shell and the development of annual growth lines in typical shells.Annual growth lines are the result of a discontinuity in the shell microstructure induced by jumping development.
LIU XiaoJunYAN ZhenGuangZHENG GuiLanZHANG GuiYouWANG HongZhongXIE LiPingZHANG RongQing
Three variants of the sequence of formation of the nacre-prism transition layer were observed in Pinctada fucata (Bivalvia, Mollusca) shells. In each case, the layer was formed by the organic matrix secreted by the mantle, together with the interprismatic organic envelope. The continuity of the organic phase throughout the shell was maintained as the new nacreous layer was formed on the nacre-prism transition layer. Changes in the interprismatic organic envelopes on either side of the nacre-prism transition zone indicated that the organic matrix of the nacre-prism transition layer becomes embedded into the organic phase of the prismatic layer. It is concluded that penetration and erosion of the prisms by the organic matrix generates a strong bond between the prismatic and nacreous layers.
LIU XiaoJunLIU ChangSUN JuanZHOU YuJuanZHENG GuiLanZHANG GuiYouWANG HongZhongXIE LiPingZHANG RongQing
