dcsimg

Caecilians (Order Gymnophona)

provided by EOL authors
Caecilians (Order Gymnophiona) and their closest fossil relatives are amphibians that are grouped as the clade Apoda. The name caecilian derives from the Latin 'caecus', meaning "blind", due to the small or sometimes nonexistent eyes. Carolus Linnaeus named the first species he described as Caecilia tentaculata (2).Gymnophona derives from the Greek for 'naked snake', as caecilians were thought to be related to snakes.

Caecilians lack limbs; smaller species superficially resemble worms, while larger species resemble snakes. The tail is short or absent and the cloaca is near the end of the body. The skin is smooth and contains calcite scales, which are probably a secondary development, rather than suggesting that caecilians are related to the fossil Stegocephalia (2). The skin has many ring-shaped folds (annuli), partially encircling the body, giving a segmented appearance. It has glands that secrete a toxin to deter predators (1).

Caecilians' vision is limited to dark-light perception (4) and their anatomy is highly adapted for burrowing. They have a strong skull and use their pointed snouts to force their way through soil or mud (2). In most species, the bones in the skull are reduced in number and fused together, while the mouth is recessed under the head. The muscles are adapted to pushing their way through the ground, with the skeleton and deep muscles acting as a piston inside the skin and outer muscles. This lets the animal anchor its hind end in position, forcing the head forwards and pulling the rest of the body up to reach it in waves. In water or very loose mud, caecilians swim like eels (1). Aquatic caecilians in the family Typhlonectidae have a fleshy fin running along the rear section of their bodies to enhance propulsion in water (5).

All but the most primitive caecilians have two sets of muscles to close the jaw; other creatures have one pair. These are more highly developed in the most efficient burrowing caecilians and seem to help keep the skull and jaw rigid (1).

Adapting to an underground life, the eyes are small and covered by skin for protection, but caecilians are not blind. Their sight is limited to simple dark-light perception. All caecilians have a pair of tentacles, located between the eyes and nostrils. These are probably used for a second olfactory capability, in addition to the normal sense of smell based in the nose (1)

Except for two lungless species (Atretochoana eiselti and Caecilita iwokramae) all caecilians have lungs, but also use their skin or mouths for oxygen absorption. Often, the left lung is much smaller than the right one, an adaptation to body shape also found in snakes.

Caecilians mostly live hidden in the ground, but some live in water. They are found in wet, tropical regions of Southeast Asia, India, Bangladesh, and Sri Lanka, parts of East and West Africa, the Seychelles, Central America, and in northern and eastern South America. In Southeast Asia, they occur as far east as Java, Borneo and the southern Philippines, but have not crossed Wallace's line and do not occur in Australia or nearby islands.

Mature caecilians seem to feed mostly on insects and other invertebrates. Captives will eat earthworms.

Caecilians use internal insemination. Males insert a penis-like organ, the phallodeum, into the female's cloaca for two to three hours. About 25% of lay eggs, which are guarded by the female. In some species, the young are already metamorphosed when they hatch; others hatch as larvae, which are not fully aquatic, but spend the daytime in the soil near the water (1). About 75% of caecilians give birth to already-developed offspring. The fetus is fed inside the female with cells lining the oviduct, which they eat with special scraping teeth.

Wilkinson et al. (8) divided the Gymnophiona into nearly 200 species and 9 families (8). A tenth family, Chikilidae, has since been discovered (9). The classification is based on morphological and molecular evidence (8,9,11,12):

Rhinatrematidae - 2 genera, 11 species; South America

Ichthyophiidae - 3 genera, 50 species; South and Southeast Asia

Scolecomorphidae - 2 genera, 6 species; Africa

Herpelidae - 2 genera, 9 species; Africa

Chikilidae - 1 genus, 3 species; India

Caeciliidae - 2 genera, 42 species; South and Central America

Typhlonectidae - 5 genera, 13 species; South America

Indotyphlidae - 7 genera, 21 species; Seychelles, India, Africa

Siphonopidae - 7 genera, 19 species; South America

Dermophiidae - 4 genera, 13 species; Africa, Central and South America

The currently accepted phylogeny is based on molecular evidence examined by Wilkinson et al. (8) San Mauro et al. (12) and with the addition of Chiklidae as its relations were determined by its describers (9)

Caecilians left a sparse fossil record. The putative earliest fossil, Eocaecilia, from the Jurassic, had small limbs and well-developed eyes (3). Anderson and co-authors (6) suggested that caecilians arose from the Lepospondyl group of ancestral tetrapods and may be more closely related to amniotes than to frogs and salamanders, which arose from Temnospondyl ancestors. Many groups of lepospondyls evolved reduced limbs, elongated bodies and burrowing behaviors. Morphological studies on Permian and Carboniferous lepospondyls have placed Eocaecilia among these groups (7). Divergent origins of caecilians and other extant amphibians may help explain the discrepancy between fossil dates for the origins of modern amphibia, which suggest Permian origins and earlier dates, in the Carboniferous, predicted by some molecular clock studies of DNA sequences. Most morphological and molecular studies of extant amphibians support monophyly for caecilians, frogs and salamanders and a molecular study based on multi-locus data suggest a Late Carboniferous–Early Permian origin of extant amphibians (10).

license
cc-by-3.0
copyright
Olingo
author
(Olingo)
partner site
EOL authors

Gymnophiona

provided by wikipedia EN

Gymnophiona is the group of amphibians that includes the legless caecilians and all amphibians more closely related to them than to frogs or salamanders (the "stem-caecilians").[2] The name derives from the Greek words γυμνος (gymnos, naked) and οφις (ophis, snake), as the caecilians were originally thought to be related to snakes. The body is cylindrical dark brown or bluish black in colour.The skin is slimy and bears grooves or ring like markings,there are minute dermal scales.

Evolution

Little is known of the evolutionary history of the caecilian lineage, which has left a sparse fossil record. The first fossil belonging to this group, a vertebra dated to the Paleocene, was not discovered until 1972.[3] The first pre-Cenozoic genus, Eocaecilia, had small limbs and well-developed eyes.[4]

In their 2008 description of the fossil batrachian Gerobatrachus,[5] Anderson and co-authors suggested that caecilians arose from the Lepospondyl group of ancestral tetrapods, and may be more closely related to amniotes than to frogs and salamanders, which arose from Temnospondyl ancestors. Numerous groups of lepospondyls evolved reduced limbs, elongated bodies, and burrowing behaviors, and morphological studies on Permian and Carboniferous lepospondyls have placed the early caecilian (Eocaecilia) among these groups.[6] Divergent origins of caecilians and other extant amphibians may help explain the slight discrepancy between fossil dates for the origins of modern amphibia, which suggest Permian origins, and the earlier dates, in the Carboniferous, predicted by some molecular clock studies of DNA sequences. Most morphological and molecular studies of extant amphibians, however, support monophyly for caecilians, frogs, and salamanders, and the most recent molecular study based on multi-locus data suggest a Late Carboniferous–Early Permian origin of extant amphibians.[7] The Late Triassic stem-caecilian Chinlestegophis from the Chinle Formation of Colorado bolsters the proposed pre-Triassic origin of Lissamphibia suggested by molecular clocks by filling a gap in the fossil record of early caecilians and suggesting that groups of stereospondyls, including Metoposauridae, are closely related to caecilians.[8]

Relationships

The most recent phylogeny of caecilians is based on molecular mitogenomic evidence examined by San Mauro et al. (2014).[9]

.mw-parser-output table.clade{border-spacing:0;margin:0;font-size:100%;line-height:100%;border-collapse:separate;width:auto}.mw-parser-output table.clade table.clade{width:100%}.mw-parser-output table.clade td{border:0;padding:0;vertical-align:middle;text-align:center}.mw-parser-output table.clade td.clade-label{width:0.8em;border:0;padding:0 0.2em;vertical-align:bottom;text-align:center}.mw-parser-output table.clade td.clade-slabel{border:0;padding:0 0.2em;vertical-align:top;text-align:center}.mw-parser-output table.clade td.clade-bar{vertical-align:middle;text-align:left;padding:0 0.5em}.mw-parser-output table.clade td.clade-leaf{border:0;padding:0;text-align:left;vertical-align:middle}.mw-parser-output table.clade td.clade-leafR{border:0;padding:0;text-align:right} Gymnophiona  

Eocaecilia micropodia

     

Rubricacaecilia monbaroni

Apoda

Rhinatrematidae

Stegokrotaphia

Ichthyophiidae

Teresomata

Scolecomorphidae

       

Chikilidae

   

Herpelidae

         

Caeciliidae

   

Typhlonectidae

       

Indotyphlidae

     

Dermophiidae

   

Siphonopidae

                   

References

Specific references:

  1. ^ Nussbaum, Ronald A. (1998). Cogger, H.G.; Zweifel, R.G., eds. Encyclopedia of Reptiles and Amphibians. San Diego: Academic Press. pp. 52–59. ISBN 0-12-178560-2..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""'"'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
  2. ^ Evans, Susan E.; Sigogneau-Russell, Denise (2001). "A stem-group caecilian (Lissamphibia: Gymnophiona) from the Lower Cretaceous of North Africa". Palaeontology. 44 (2): 259. doi:10.1111/1475-4983.00179.
  3. ^ Estes, Richard; Wake, Marvalee H. (22 September 1972). "The First Fossil Record of Caecilian Amphibians". Nature. 239 (5369): 228. doi:10.1038/239228b0. Retrieved 18 August 2009.
  4. ^ Jenkins, Parish A.; Walsh, Denis M. (16 September 1993). "An Early Jurassic caecilian with limbs". Nature. 365 (6443): 246. doi:10.1038/365246a0. Retrieved 18 August 2008.
  5. ^ Anderson, Jason S.; Reisz, Robert R.; Scott, Diane; Fröbisch, Nadia B.; Sumida, Stuart S. (2008). "A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders". Nature. 453 (7194): 515–8. doi:10.1038/nature06865. PMID 18497824.
  6. ^ Huttenlocker, A. K.; Pardo, J. D.; Small, B. J.; Anderson, J. S. (2013). "Cranial morphology of recumbirostrans (Lepospondyli) from the Permian of Kansas and Nebraska, and early morphological evolution inferred by micro-computed tomography". Journal of Vertebrate Paleontology. 33 (3): 540. doi:10.1080/02724634.2013.728998.
  7. ^ San Mauro, D. (2010). "A multilocus timescale for the origin of extant amphibians". Molecular Phylogenetics and Evolution. 56 (2): 554–561. doi:10.1016/j.ympev.2010.04.019. PMID 20399871.
  8. ^ Jason D. Pardo; Bryan J. Small; 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 114 (27): E5389–E5395. doi:10.1073/pnas.1706752114.
  9. ^ San Mauro, D.; Gower, D. J.; Müller, H.; Loader, S. P.; Zardoya, R.; Nussbaum, R. A.; Wilkinson, M. (2014). "Life-history evolution and mitogenomic phylogeny of caecilian amphibians". Molecular Phylogenetics and Evolution. 73: 177–189. doi:10.1016/j.ympev.2014.01.009. PMID 24480323.

license
cc-by-sa-3.0
copyright
Wikipedia authors and editors
original
visit source
partner site
wikipedia EN

Gymnophiona: Brief Summary

provided by wikipedia EN

Gymnophiona is the group of amphibians that includes the legless caecilians and all amphibians more closely related to them than to frogs or salamanders (the "stem-caecilians"). The name derives from the Greek words γυμνος (gymnos, naked) and οφις (ophis, snake), as the caecilians were originally thought to be related to snakes. The body is cylindrical dark brown or bluish black in colour.The skin is slimy and bears grooves or ring like markings,there are minute dermal scales.

license
cc-by-sa-3.0
copyright
Wikipedia authors and editors
original
visit source
partner site
wikipedia EN