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Diplopleurozoa (phylum Cnidaria) Extinct, primitive class, known only from the Lower Cambrian, whose members have a bell-shaped body of elliptical outline, showing distinct bilateral symmetry. There is a median furrow along the main axis of the body, from which arise numerous, flat, simple segments which reach the periphery and are separated by narrow grooves. The margins are scalloped into short lappets, each bearing a simple tentacle.