Dumb Question??? Is there a difference between the O2 sensor and the Mass Air Flow Sensor?

Still trying to chase a rich fuel problem and wondering: (1) the question above; and (2) if there might be a MAF sensor on my 500SL. The O2 sensor has been replaced and that made no difference. So, if there is a MAF sensor, this might be a possibility.

Thanks,

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Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000