Heterocercal

Heterocercal (Gr. hetēros, 'unequal,' and kērkos, 'tail'), Agassiz term for the tail of Elasmobranch and most Ganoid fishes, in which the vertebral axis is bent upwards in the tail, making the upper lobe much the larger (see the article STURGEON). In bony fishes also the axis is somewhat bent upwards in its termination, but the asymmetry is disguised, and the tail looks equal-lobed or homocercal. In some Teleosts and Ganoids, in a few Elasmobranchs, and in Dipnoi, the tail is genuinely symmetrical or diphycercal.