Special Growth Morphology and Genesis of Nacreous Layer of Hyriopsis Cumingi from E'zhou, Hubei Province

The growth morphology of nacreous layer of shell of freshwater Hyriopsis Cumingi from E’zhou, Hubei Province, is studied by using the polarizing microscope.The results indicate that, besides the normal shape of sheet,the special morphology of crystallization aggregates in nacreous layer consists of the highlight band, tiny fibrous layer, prismatic layer and yellowish brown band or zone.The formation of highlight band and tiny fibrous layer is associated with the abnormal secretion of epithelial cell on the mantle tissues. The prismatic layer on the growth root of the shell may be the texture of recrystallization caused by the external mechanic force. The content variation of organic matrix in the yellowish-brown band or zone shows that mussel’s metabolization gradually retrieves from the abnormal to the normal states. The parallel laminations in the nacreous layer indicate that the secretion surface of mantle tissues maintains constant migration from the root to the rim of shell. The growth laminations on both sides of the prismatic layer suggest the two movement directions of secretion surface of mantle tissues, one is from the mussel’s growth root to the rim on the internal surface of the shell,the other is from the external to the internal of the shell vertically to the nacreous layer.