Definition of heterocercal in US English:

heterocercal

adjective

Zoology
  • (of a fish's tail) having unequal upper and lower lobes, usually with the vertebral column passing into the upper.

    Contrasted with diphycercal, homocercal
    • ‘The sturgeon heterocercal tail is extremely flexible and the upper tail lobe trails the lower during the fin beat cycle.’
    • ‘They also have a cartilaginous skeleton, heterocercal tail, and lack scales.’
    • ‘While the classical view of shark tail function was corroborated by the three-dimensional kinematic study of leopard sharks, the pattern of heterocercal tail function in sturgeon proved to be quite different.’
    • ‘The tail is heterocercal, with the upper lobe containing long, thread-like filaments.’
    • ‘The body shows well-developed paired lateral fins (presumably true pectoral fins), indicating good stability, dorsal and anal fins, and a heterocercal tail (the lower lobe of the tail is elongated).’

Origin

Mid 19th century: from hetero- ‘other’ + Greek kerkos ‘tail’.

Pronunciation

heterocercal

/ˌhedərōˈsərk(ə)l/