1 - gill cover
2 - side line
3 - dorsal fin
4 - fat fin
5 - tail stem
6 - tail fin
7 - anal (sub-caudal) fin
8 - photophores
9 - ventral fin (doubles)
10 - pectoral fin (paired)
A) heterocercal
B) protocercular
C) homocercal
D) difitserkalny
The tail fin is the fin located on the tail of many aquatic animals: jawless , fish , some marine mammals ( cetaceans and sirens ), as well as some extinct marine reptiles. Its shape is closely related to the type of movement.
There are such types of caudal fins:
- 1. Protocercal ( primary-symmetrical ) - caudal fin, not bifurcated into two blades. Only in fish larvae .
- 2. Heterocercal - the caudal fin with lobes of significantly different lengths, with the upper lobe longer and the caudal spine entering into it. It is characteristic of cartilaginous and sturgeon-like fish (as well as for most of the shell-shaped and part of the lobedfish [1] ).
- 3. The reverse hetero -cercal ( hypo-cercal ) - caudal fin with lobes of significantly different lengths, the lower lobe being longer and the caudal spine (or end of the chord ) entering it . It is characteristic of ichthyosaurs , mosasaurs, and many (but not all) ostracoderms [2] [3] .
- 4. Homocercal - the caudal fin with lobes of the same size, with the end vertebrae of the spinal column merging into a rod-shaped bone ( urostyle , English urostyle ), which enters the base of the upper lobe of the fin, and the base of the lower lobe is supported by overgrown, rather wide lower arches of the vertebrae - hypurals . It is characteristic for the majority of ray-finned fish .
- 5. Difitserkalny - caudal fin, merging with the dorsal and anal fins. It is characteristic of a part of lapellate and some armored fish [1] .
Unpaired fins lacking a skeleton are found in amphibian larvae, in adult tailed amphibians, and some other animals. In cetaceans and sirens, the tail fins are equally lobed (symmetrical), but are located in the horizontal plane, since the ancestors of these animals retained the inherent ability of all mammals to bend when moving the body in a vertical plane when they returned to the aquatic environment.
Bony fish tail fin skeleton
The mechanical supporting structure of the caudal fin in fish is the skeleton . The muscles controlling the fin and the rays of the fin are attached to the skeleton of the caudal fin. Among the main elements of the skeleton of the caudal fin distinguish [4] :
- urostyle , or urosticular complex, which is a complex of several oral vertebrae , merged into a single bone during evolution;
- hypuralia - the lower bony elements attached to the ventral side of the urostyle and supporting the main rays of the fin;
- epuralia - the upper bony elements lying above the dorsal side of the urostyle;
- the upper and lower caudal cartilages found in many fish supporting the marginal rays of the caudal fin.
Notes
- ↑ 1 2 Cherepanov G.O., Ivanov A.O. Paleozoology of vertebrates. - M .: Publ. Center "Academy", 2007. - 352 p. - ISBN 978-5-7695-3104-0 . - S. 79, 142.
- ↑ Carroll R. Paleontology and evolution of vertebrates: In 3 volumes T. 1. - M .: Mir, 1992. - 280 p. - ISBN 5-03-001819-0 . - S. 37–55.
- ↑ Nelson J.S. Fish of the World Fauna. 4th ed. - Moscow: URSS, 2009 .-- 880 p. - ISBN 978-5-397-00675-0 . - S. 73-80.
- ↑ Bogutskaya N.G., Naseka A.M., Gerd A.S. Russian-Latin-English explanatory dictionary of terms // Nelson J.S. Pisces of World Fauna / Transl. 4th English ed. - M .: Book House "LIBROCOM", 2009. - 880 p. - ISBN 978-5-397-00675-0 . - S. 727-800.