Thornback eels
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| Gosline , 1960 |
The thorn-back eel-like (Notacanthiformes ( Gr .:, “Noton” = back, “akantha” = thorn, Lat .: “Forma” = shape)) are an order of marine bony fish . The marine fish live worldwide in the deep sea between 125 and 4900 meters, mostly between 450 and 2500 meters.
features
Thorn-back eels have an elongated, eel-like, pointed body with a long anal fin that is about half the length of the body and has grown together with the rudiments of the caudal fin. The caudal fin skeleton is reduced or absent. If lost, the tail is easily regenerated. The pectoral fins sit relatively high on the body, the pelvic fins standing far below are supported by 7 to 11 fin rays. The gill membranes are separated. The number of Branchiostegal rays is from 5 to 23. A relatively large swim bladder is present. The mouth is below, the teeth are small. The intestine is short and there are some pyloric tubes . Some species have luminous organs . Thorn-back eels are 10 cm to 1.2 meters long.
Notacanthiformes are only three synapomorphies defined :
- A large connective tissue node is embedded between the wing bone and the maxillary.
- The maxillary has a backward spine on the back of its upper edge.
- The pelvic fins are usually connected by a membrane.
Larvae
The leptocephalus larvae of the thorn-back eel are longer than the adult animals, a maximum of two meters. The transparent larvae show more than 300 V-shaped muscle segments . A normal caudal fin is missing, but a thread-like extension is found. The dorsal fin is short and is supported by about ten fin rays. It is located behind the middle of the body. Older larvae have small pelvic fins. Some Leptocephalus larvae of the thorn- back eels have been described as separate species under the generic names Tilurus and Tiluropsis .
External system
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After Wiley & Johnson, 2010
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After Nelson, 2006
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The systematic position of the thorn-back eel-like within the Elopomorpha and their sister group is still controversial. The American ichthyologist Joseph S. Nelson puts them in his standard work on the fish system Fishes of the World as a subordination Notacanthoidei to the order of the fish-like (Albuliformes). Wiley & Johnson list nine synapomorphies for a sister group relationship between the thorn-back eels and the eels (Anguilliformes). The two cladograms show the alternative possibilities for the systematic position of the thorn-back eel-like:
Internal system
There are two families, six genera and about 27 species.
- Lizard eels (Halosauridae)
- Thornback eels (Notacanthidae)
literature
- Kurt Fiedler: Textbook of Special Zoology, Volume II, Part 2: Fish , Gustav Fischer Verlag, Jena 1991, ISBN 3-334-00339-6 .
- Joseph S. Nelson : Fishes of the World . John Wiley & Sons, 2006, ISBN 0-471-25031-7 .
- EO Wiley & G. David Johnson: in A teleost classification based on monophyletic groups. in Joseph S. Nelson, Hans-Peter Schultze & Mark VH Wilson: Origin and Phylogenetic Interrelationships of Teleosts. Publishing house Dr. Friedrich Pfeil, Munich 2010, ISBN 978-3-89937-107-9 .
Web links
- Thornback Eels on Fishbase.org (English)