Neurosecretory cell types in the eyestalk of the freshwater prawn Palaemon paucidens: an electron microscopic study.

In the medulla terminalis ganglionic X-organ (MTGX) of the eyestalk of the freshwater prawn, Palaemon paucidens, six peptidergic neurosecretory cell types (A-, B-, C-, D-, E-, and F-cells) are distinguishable on the basis of the different morphology of their elementary granules and rough endoplasmic reticulum (rER). All of these cell types seem to correspond to Type-IIIa cells or dispersing Type-IV cells, that have previously been differentiated at the light microscopic level (Hisano, 1974), as judged from the dimensions of their cell bodies and nuclei. Two other peptidergic neurosecretory cell types that are apparently comparable to the Type-II and Type-IIIb cells (Hisano, 1974), respectively, are recognized in parts of the optic ganglia other than MTGX, and these are now designated as G- and H-cells, respectively. All the remaining cell types, designated as Type-I, cluster-forming Type-IV, Type-V and Type-VI cells in our previous light microscopic study, have small cored-vesicles in their cytoplasm. It remains undecided whether these, possibly aminergic, neurons are neurosecretory or not.