Dictionary of Ichthyology  

gephyrocercal = a secondary condition of symmetry in the caudal fin where the original caudal fin has been lost and the interval is bridged by caudal elements. Symmetrical internally and externally, e.g. Mola, Fierasfer, Carapus. Sometimes applied to any secondary internal symmetry - a synonym of diphycercal.
Tail of Mola mola from "A Guide to the Study of Fishes" by D. S. Jordan, 1905. Photograph by Brian W. Coad.

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