Two neuronal chromoproteins (red-haemoprotein and yellow-carotenoprotein) initiate changes in ciliary activity on the gill of Mytilus. Photic, electrical and chemical stimulation of these chromoproteins correlate with fluctuations in ionic (calcium and iron) deposits in gill bulk tissue samples. Microspectrophotometric measurements of chromoprotein spectral band patterns reveal two or three absorption maxima for carotenoprotein and haemoprotein respectively. Under aerobic conditions, cilioinhibition and cilioexcitation results after activation of carotenoprotein or haemoprotein respectively. Carotenoproteins are only engaged during gradual anoxia. Immediate anoxia renders both chromoproteins inoperative. Changes in ciliary activity initiated by photic stimulation of neuronal chromoproteins are abolished by denervation of the gill. It is postulated that photoactivation and/or release of specific neurotransmitters lead to transformations in chromoproteins with subsequent neuronal regulation of gill ciliary activity.

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