from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Relating to, having, or being a tail fin in which the upper lobe is larger than the lower and the vertebral column extends into the upper lobe, as in sharks.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. Of a fish's tail, such that the vertebral column bends and extends upwards into the upper lobe of the tail, making it larger than the lower lobe; as in sharks, rays, and skates.
from the GNU version of the Collaborative International Dictionary of English
- adj. Having the vertebral column evidently continued into the upper lobe of the tail, which is usually longer than the lower one, as in sharks.
from The Century Dictionary and Cyclopedia
- In ichthyology, having an unequally divided tail or caudal fin. Contrasted with homocercal.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adj. possessing a tail with the upper lobe larger than the lower and with the vertebral column prolonged into the upper lobe
This so called heterocercal tail is only known to exist, as a permanent adult feature, in the sturgeons of to-day.
Paddlefish are not closely related to sharks, but they do share some common characteristics including a skeleton primarily composed of cartilage, and a deeply forked, abbreviate heterocercal tail fin (the top fin lobe is slightly larger than the lower fin lobe).
These are the even-lobed, or homocercal (Fig. 68), and the uneven-lobed, or heterocercal (Fig. 69).
Now, in the development of a teleost fish (Fig. 68), as has been shown by Alexander Agassiz, the tail-fin is first like Fig. 70; then becomes heterocercal, like Fig. 69; and, finally, becomes homocercal like Fig. 68.
The lecturer dwelt chiefly on the argument of Agassiz, which he summarises as follows: "Homocercal fishes have in their embryonic state heterocercal tails; therefore heterocercality is, so far, a mark of an embryonic state as compared with homocercality, and the earlier heterocercal fish are embryonic as compared with the later homocercal."
Their tails, too, though both heterocercal, were diverse in their type.
Then with all his force the captain drove the pole down; the aim was good, for the next instant there was a tremendous swirl in the water, the long, heterocercal tail, through which the creature's spine was continued to the end of the upper lobe, rose above the surface, and was brought down with a tremendous blow which raised a shower, and at the same time Captain Bradleigh's arms were dragged lower and lower, till he loosened his hold, and the pole of the boat-hook disappeared.