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Related to Homocercal Fin: heterocercal fin
the superficially symmetrical caudal fin of bony fish, in which the axial skeleton does not continue within the fin plate, which is formed from dermal rays alone. The homocercal fin arises in phylogenesis by means of the reduction of the axial skeleton in the upper lobe of the heterocercal fin. The internal asymmetry is retained inasmuch as the hypurals support the upper as well as the lower lobe.