Ultrastructure of the mandibular organ of the shrimp, Penaeus japonicus, in untreated and experimentally manipulated individuals.

The fine structure of the mandibular organ of the shrimp, Penaeus japonicus, was studied. The cells of mandibular organ contain mitochondria, smooth endoplasmic reticulum and Golgi complex. These organelles do not show any change during molt cycle. Prominent changes were observed in the cells after some steroids or proteinaceous substance. Some changes in the cells also occurred after the eyestalks were ablated. The function of the mandibular organ was considered.