Chloride cells of larval Notonecta glauca and Naucoris cimicoides (Hemiptera, Hydrocorisae). Fine structure and cell counts at different salinities.

The chloride cells of the larval waterbugs, Notonecta glauca L. and Naucoris cimicoides L., ultrastructurally resemble the caviform chloride cells of other aquatic insects as well as those of teleost fish. The predominant features are abundant mitochondria, basolateral plasma membrane infoldings and an apical cavity possessing numerous microvilli. After histochemical precipitation of chloride, dense deposits of silver chloride are present in the apical region. The cuticular area overlying the chloride cells is extremely reduced in thickness and differentiated into a plug-like structure. The 1st instars of Notonecta glauca raised from the eggs at various hypo-osmotic salt concentrations have identical numbers of thoracal chloride cells regardless of the external salinity. The number of cells progressively increases with each moult. However, in corresponding larval stages, there is a significant decrease in the number of thoracal chloride cells relative to increases in the external salinity. These results are consistent with the presumptive involvement of the chloride cells in osmotic hyperregulation.