Doppler ultrasound is a type of ultrasound that depends on the Doppler Effect, a change in the wave's frequency, which can occur from the motion of a reflector, such a red blood cell. We experience the Doppler Effect when, for example, an ambulance approaches us, passes and then drives away.
Definition of PLACODERM. : any of a class (Placodermi) of extinct chiefly Devonian fishes with an armor of bony plates and primitive jaw structures.ADVERTISEMENT. New Latin Placodermi, ultimately from GK plak-, plax + derma skin â more at derm-. any of a class (Placodermi) of extinct chiefly Devonian fishes with an armor of bony plates and primitive jaw structures. ADVERTISEMENT.
Fish Classification. The classification of fishes has undergone much change over the last few decades, and further changes are expected, partly because so many groups are poorly known.wo classes are extinct groups of fishes. Class Placodermi. An extinct group of fishes with bony plates covering the head, living from the Silurian to the Upper Devonian (443 to 360 million years ago); some are known from Canada.