Mexican dermal root ( Dermophis mexicanus )
|Müller , 1832|
The Caecilian (Gymnophiona, Apoda) or Caecilians form of almost 200 kinds of the smallest order in the class of amphibians (Amphibia). Despite the name caecum, they are neither completely blind nor do any species root in the ground.
Sneak amphibians have no limbs, and the tail is also greatly reduced. The cloaca is at the rear end of the body, which often resembles the front end. Small sneak amphibians (around 10 centimeters in length) can easily be mistaken for earthworms , while large species (around 1 to 1.6 meters in length) appear snake-like.
The skin of the sneak amphibian is smooth and often dull dark in color. Some species have colored stripes or spots on the sides. In the past, they were regarded as related to the extinct tank burrows due to the calcareous scales embedded in the skin and the fused skull bones ; today these properties are interpreted as secondary adjustments. The jaw and palate have teeth.
The alternative name, blindwheels, is derived from the eyes, which are often receded and covered by skin, which can therefore only see simple light-dark contrasts. Perception occurs mainly through smelling and with two feelers between the nose and eyes. Floor vibrations also play a role in orientation. The respiration takes place through the right lung, is back usually formed while the left. Gas exchange also takes place via the skin and the oral mucosa, especially in the lungless caecum. From the latter, however, no observations on living animals are known, even if in 2010 another species was known from Venezuela in addition to the Atretochoana eiselti , known only in two preserved specimens .
Sneak amphibians occur in the tropics and subtropics of Southeast Asia , Africa, and Central and South America . They usually reside in the upper soil and litter layers of forests and live on small animals, especially earthworms . They prefer wet areas, often near bodies of water. Poolworms, which have fully adapted to aquatic life, are found in slow-flowing rivers such as the Amazon , Orinoco, and the Colombian river systems.
Because of their hidden way of life, the sneak amphibians are a little-known group of amphibians. Zoologists assume that not all species have yet been described.
Reproduction and development
The insemination takes place inside the body of the female. The male has a mating organ that can be extended out of the cloaca for sperm transfer, the so-called phallodeum.
There are egg-laying species, but around 75% of the species are viviparous. The young hatch in the womb and are fed in the fallopian tubes before they are born. The gestation period of the females can be up to 10 months. The egg-laying species lay their eggs in burrows on land. The oviposition sites require a certain amount of moisture and substrate, and the dams often have to wander long distances to the appropriate places. Caeces also move more over land during the mating season, usually at night and when it rains. In some species brood care is known; in the first two months the mother's skin serves as food. The young animals live amphibiously - they are in the water for night hunting, during the day they are buried in the bank area.
The majority of the caecilians are specialized earthworm hunters. Burrowing caecilians are only found where earthworms are also found in the ground. To do this, there must be constant moisture in the soil, it is not found in places with greater drought. However, they can retreat deep into the ground together with the earthworms in the dry season. The stomachs of the Afrocaecilia taitana species contained termite capsules , but most of the stomach contents were organic matter that could not be identified. Some species also eat insect larvae, termite pupae and ants - but adult termites and ants are too quick to prey on. The aquatic swimming burrows ( Typhlonectes ) are also scavengers and help to remove deceased fish and mollusks, but they cannot prey on live fish. However, their main prey in the water are worms and other mollusks. They can easily be attracted to the biotope with dead fish. The Brazilian-Argentine swamp burrows ( Chthonerpeton ) are something between aquatic swimming burrows and the burrowing species.
As studies by Thomas Kleinteich from the University of Jena show, blind burrows reach an astonishing age. The long gestation period of up to 10 months and the late achievement of reproductive capacity at 10–12 years suggest that the adult stage can last a long time - it is estimated that the larger species can live to be around 80 years - if they do not beforehand fall prey to an enemy. Caecilians have few enemies, and many species also protect themselves with poisonous skin secretions. As Daniel Hofer was able to prove, the West African buntwühle (Schistometopum), for example, has an effective skin poison that causes other vertebrates in the same container to die within 2 days. As a specialized caecilians hunters some erdwühlende snakes are known as the East Asian rolling snake ( Cylindrophis ).
During the up to 10-year youth phase, significant physical changes gradually take place. This may have led to various stages of youth being described as separate species in the past. In the case of species in particular, of which only one or two specimens are known today, genetic investigations still have to be carried out to determine whether they are own species or just juvenile phases of a known species.
The Rhinatrematidae, as the most primitive family, are compared to all other families as sister groups . The probable relationship of the families to one another, determined with the help of DNA sequencing , shows the following cladogram :
The sneak amphibians are divided into ten families and sometimes grouped according to their level of development.
- Family Caeciliidae Rafinesque, 1814 - burrows
- Family Chikilidae Kamei et al., 2012
- Family Dermophiidae Taylor, 1969
- Herpelidae Laurent family , 1984
- Family Ichthyophiidae Taylor, 1968 - Fish rooting
- Family Indotyphlidae Lescure, Renous & Gasc, 1986
- Family Rhinatrematidae Nussbaum, 1977 - nasal rooting
- Family Siphonopidae Bonaparte, 1850
- Family Scolecomorphidae Taylor, 1969 - Grave digging
- Typhlonectidae Taylor family , 1968
The exact number of genera and species within each family fluctuates depending on authority, especially because many species are only described by a single specimen copy.
Until 1993, sneak amphibians were only known to be fossilized from two fossil eddies from the Upper Cretaceous of Bolivia and the Paleocene of Brazil . Finally, in 1993, Eocaecilia was described, a sneaking amphibian from the Lower Jurassic that still had four short extremities with three toes each. Chinlestegophis is even older . The genus belongs to the parent group that leads to the sneak amphibians and lived in what is now North America in the Triassic . The fossils were found in the Chinle Formation . The skull of Chinlestegophis shows a mix of features between today's sneak amphibians and the stereospondyli , a group of the temnospondyli and is therefore an indication that today's amphibians have emerged from the temnospondyli.
- Amphibian Species of the World 6.0, Gymnophiona Müller, 1832 (Engl.)
- Database "Amphibian Species of the World" (Engl.)
- globalamphibians.org (Engl.)
- Werner Himstedt: The blind diggers. 1996, ISBN 3-89432-434-1 .
- Daniel Hofer: Blind burrows in the wild and in captivity. In: Herpetozo. Reports of the Austrian Society for Herpetology. Volume 11, Issue 1/2, July 1998, .
- Rachunliu G. Kamei, Diego San Mauro, David J. Gower, Ines Van Bocxlaer, Emma Sherratt, Ashish Thomas, Suresh Babu, Franky Bossuyt, Mark Wilkinson, SD Biju: Discovery of a New Family of Amphibians from Northeast India with Ancient Links to Africa. In: Proceedings of the Royal Society B . 2012, pp. 1–6. doi: 10.1098 / rspb.2012.0150 .
- M. Wilkinson, D. San Mauro, E. Sherratt, DJ Gower: A nine-family classification of caecilians (Amphibia: Gymnophiona). In: Zootaxa . 2874, 2011, pp. 41-64. (online) ( Memento from December 14, 2012 in the web archive archive.today )
- Amphibian Species of the World 6.0, Gymnophiona Müller, 1832 (Engl.)
- AmphibiaWeb: Atretochoana eiselti
- Marvalee H. Wake, Maureen A. Donnelly: A new lungless caecilian (Amphibia: Gymnophiona) from Guyana. In: Proc. R. Soc. B. vol. 277, no. 1683, March 22, 2010, pp. 915-922. doi: 10.1098 / rspb.2009.1662
- Baby cannibals. ( Memento from February 12, 2013 in the web archive archive.today ) Friedrich Schiller University Jena.
- Rachunliu G. Kamei include: Discovery of a New Family of Amphibians from North East India with Ancient links to Africa. In: Proceedings of the Royal Society B . 2012, p. 3.
- Farish A. Jenkins, Denis M. Walsh: An Early Jurassic caecilian with limbs. In: Nature . 365, 1993, pp. 246-250, DOI: 10.1038 / 365246a0
- Jason D. Pardo, Bryan J. Small, and Adam K. Huttenlocker. 2017. Stem Caecilian from the Triassic of Colorado Sheds Light On the Origins of Lissamphibia. Proceedings of the National Academy of Sciences of the United States of America. July, 2017, DOI: 10.1073 / pnas.1706752114