Description

Caecilians completely lack limbs, making the smaller species resemble worms, while the larger species, with lengths up to 1.5 m (4 ft 11 in), resemble snakes. Their tails are short or absent, and their cloacae are near the ends of their bodies. !" #" 4" Their skin is smooth and usually dark$matte, but some species ha%e colorful skins. &nside the skin are calcite scales. 'ecause of these scales, the caecilians were once thought to be related to the fossil (tegocephalia, but they are now belie%ed to be a secondary de%elopment, and the two groups are most likely unrelated. 4" The skin also has numerous ring$shaped folds, or annuli, that partially encircle the body, gi%ing them a segmented appearance. )ike some other li%ing amphibians, the skin contains glands that secrete a to*in to deter predators. 1" The skin secretions of Siphonops paulensis ha%e been shown to ha%e hemolytic properties. 5" Caecilians+ %ision is limited to dark$light perception, ," and their anatomy is highly adapted for a burrowing lifestyle. They ha%e a strong skull, with a pointed snout used to force their way through soil or mud. 4" &n most species, the bones in the skull are reduced in number and fused together, and the mouth is recessed under the head. Their muscles are adapted to pushing their way through the ground, with the skeleton and deep muscles acting as a piston inside the skin and outer muscles. This allows the animal to anchor its hind end in position, and force the head forwards, and then pull the rest of the body up to reach it in wa%es. &n water or %ery loose mud, caecilians instead swim in an eel$like fashion. 1" Caecilians in the family Typhlonectidae are a-uatic, and the largest of their kind. The representati%es of this family ha%e a fleshy fin running along the rear section of their bodies, which enhances propulsion in water. ." /ll but the most primiti%e caecilians ha%e two sets of muscles for closing the 0aw, compared with the single pair found in other creatures. These are more highly de%eloped in the most efficient burrowers among the caecilians, and appear to help keep the skull and 0aw rigid. 1" /dapting to their underground life, the eyes are small and co%ered by skin for protection, which has led to the misconception that they are blind. This is not strictly true, although their sight is limited to simple dark$light perception. /ll caecilians possess a pair of tentacles, located between their 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" 1*cept for two lungless species 2 Atretochoana eiselti 3" and Caecilita iwokramae 4" 2 all caecilians ha%e lungs, but also use their skin or mouths for o*ygen absorption. 5ften, the left lung is much smaller than the right one, an adaptation to body shape that is also found in snakes.
citation needed"

Distribution
Caecilians are found in wet, tropical regions of (outheast /sia, &ndia, 'angladesh, and (ri )anka, parts of 1ast and 6est /frica, the (eychelles &slands in the &ndian 5cean, Central /merica, and in northern and eastern (outh /merica. &n /frica, caecilians are found from

7uinea$'issau (Geotrypetes) to southern 8alawi (Scolecomorphus), with an unconfirmed record from eastern 9imbabwe. They ha%e not been recorded from the e*tensi%e areas of tropical forest in central /frica. &n (outh /merica, they e*tend through subtropical eastern 'ra:il well into temperate northern /rgentina. They can be seen as far south as 'uenos /ires, when they are carried by the flood waters of the ;aran< =i%er coming from farther north. Their /merican range e*tends north to southern 8e*ico. The northernmost distribution is of the species Ichthyophis sikkimensis of northern &ndia. Ichthyophis is also found in (outh China and >orth ?ietnam. &n (outheast /sia, they are found as far east as @a%a, 'orneo, and the southern ;hilippines, but they ha%e not crossed 6allace+s line and are not present in /ustralia or nearby islands. citation needed"

Taxonomy

Ichthyophis from the (an /ntonio 9oo The name caecilian deri%es from the )atin word caecus, meaning AblindA, referring to the small or sometimes none*istent eyes. The name dates back to the ta*onomic name of the first species described by Carolus )innaeus, which he named Caecilia tentaculata. 4" The order name deri%es from the 7reek words BCDEFG (gymnos, naked) and FHIG (ophis, snake), as the caecilians were originally thought to be related to snakes. citation needed" The most recent classification of caecilians, by 6ilkinson et al. (!J11), di%ided the 7ymnophiona into 4 families containing nearly !JJ species. 1J" (ince then, a tenth caecilian family has been disco%ered, Chikilidae. 11" 1!" This classification is based on a thorough definition of monophyly based on morphological and molecular e%idence, 1#" 14" 15" 1," and it sol%es the longstanding problems of paraphyly of the Caeciliidae in pre%ious classifications without an e*clusi%e reliance upon synonymy. 1J" 1."

=hinatrematidae $ ! genera, 11 speciesK (outh /merica &chthyophiidae $ # genera, 5J speciesK (outh and (outheast /sia (colecomorphidae $ ! genera, , speciesK /frica Lerpelidae $ ! genera, 4 speciesK /frica Chikilidae $ 1 genus, # speciesK &ndia Caeciliidae $ ! genera, 4! speciesK (outh and Central /merica

Typhlonectidae $ 5 genera, 1# speciesK (outh /merica &ndotyphlidae $ . genera, !1 speciesK (eychelles, &ndia, /frica (iphonopidae $ . genera, 14 speciesK (outh /merica Mermophiidae $ 4 genera, 1# speciesK /frica, Central and (outh /merica

The most recent phylogeny of caecilians is based on molecular mitogenomic e%idence e*amined by (an 8auro et al. (!J14)