Gymnophiona

## About

Gymnophiona refers to an order of legless, serpentine amphibians, known as caecilians. The word caecilian is derived from the Latin *caecus*, meaning 'blind', in reference to the caecilian's blindness. Caecilians are not restricted to a single continent, being abundant throughout South America, Africa (Central) and Southeast Asia. Due to morphological similarities, gymnophionans were once classed as the closest relatives to snakes however, this is now known to be inaccurate, with caecilians being better classed as amphibians. Unfortunately, little is known about the evolutionary history and classification of caecilians. Though none of the families in this order are extinct, many of its members are sometimes referred to as 'living fossils' for their primitive appearance and nature, reminiscent of extinct amphibians.

## Extant Families

#### Rhinatrematidae

Rhinatrematidae, or the tailed-caecilians is usually sighted as the most primitive form of the caecilian order. Rhinatrematids are primitive even when compared to other caecilians, possessing numerous features of which other families lack. For example, rhinatrematids are visually different, having tails, external gills to support their aquatic lifestyle and mouths that are not located on the undersides of their heads. Beyond appearance based differences, rhinatrematids also exhibit behavioural differences, including their habit of laying eggs in soil crevasses and cavities and hiding in seepage areas until they perform their metamorphosis into their mature form. Rhinatrematids are also unique in that they are one of the few caecilian families which birth larval juveniles, rather than fully metamorphosed juveniles.

#### Icthyophiidae

Icthyophiidae is a family of Southeast Asian tailed-caecilians, also known for their primitive appearance. Unlike the also basal rhinatrematids, icthyophiids possess two sets of jaw-closing muscles. Other than this morphological difference, the family is similar to rhinatrematids in their differences to less-primitive caecilians, also having tails, external gills and a differently positioned mouth. Both families also share the behavioural characteristics of hiding in seepages and laying their eggs in dirt, as well as both families rearing larval young. Evidence has also been found that icthyophiid females defend their egg clutches.

#### Scolecomorphidae

Scolecomorphids are a family of caecilians which live only in Western and Eastern Africa, specifically in the countries of Cameroon, Tanzania and Malawi. scolecomorphids are also known as buried-eyed caecilians, as they only possess primitive vestigial eyes. Interestingly, scolecomorphids are also known to possess tendrils at the sides of their snouts. Members of scolecomorphidae also have grooves which circle their bodies, giving them a segmented appearance, common in other families. Unlike rhinatrematids and icthyophiids, scolecomorphids produce fully metamorphosed young, as opposed to the larval young common between the other two families.

#### Herpelidae

Herpelidae is a family also native to Africa however, it has a wider range, being distributed throughout sub-Saharan Africa. They are most commonly sighted for being the sister-family to chikilidae. They are the only other family to be exclusive to the African continent.

#### Chikilidae

Chikilids are a family that is found throughout Northeast India and is the most recently discovered gymnophionan family, being first discovered in 2012. Though this is the newest family, one of its members, the Kuttal caecilian ***(Chikila fulleri)***, is not new to science, having being discovered in 1904 and being placed in the Herpelidae family. Herpetologist Sathyabhama Das Biju of the University of Delhi, claims that as many as seven species of chikilid exist in every Northeast Indian province/state. Evidence suggests that chikilidae originated in Africa, similarly to that of its sister-family, Herpelidae. It has been said that chikilid caecilians are extremely devoted mothers, defending their eggs by coiling their bodies around them for months. Similarly to 75% of caecilians, chikilid young are already fully metamorphosed after hatching, rather than being larval.

#### Caeciliidae

Caeciliidae or the common caecilian family, is a family comprised of 44 species of caecilian endemic to areas of Central and South America, it is the largest and most diverse gymnophionan family. Though caeciliids lack some of the physical attributes found in primitive caecilians, such as their lack of a tail, specialised ramming skulls and oral positioning, they share the attribute of laying larval young and also laying their eggs in soil crevasses. Also similarly to basal groups, caeciliids are also known to hide in seepages when in their larval stage. Though it is the norm for caeciliids to rear larval offspring, some species have exhibited fully metamorphosed hatchlings.

#### Typhlonectidae

Typhlonectidae is another South American caecilian family. The members of this family can typically only be found within the range of the tropical Andes in Western South America. This family also includes the largest caecilian, the Eiselt's caecilian ***(Atretochoana eiselti)***. Some variation in the lifestyles of the genera can be found within the family in the form of their habitat preferences. To elaborate, the genera of Potamotyphlus and Typhlonectes live a completely aquatic life, whereas members of Chthonerpeton and Nectocaecilia are capable of land locomotion and are thus classed as semi-aquatic species, similarly to most other extant Amphibians.

#### Grandisoniidae

Grandisoniidae was formerly known as Indotyphlidae and many of its current members were at points classed as belonging to caeciliidae. In 2011, the genera Gegeneophis, grandisonia, Hypogeophis, Idiocranium, Indotyphlus, Praslinia and Sylvacaecilia were first placed into grandisoniidae, (at the time named Indotyphilidae). The reasoning for the name change is interesting, in that the family's Indian genera were originally named after Indotyphlini tribe however, it was later changed due to the nomenclature rule stating that grandisoniidae held a higher rank when compared to Indotyphlidae.

#### Siphonopidae

Siphonopidae is a family of caecilians commonly referred to also as common caecilians, for their range in Central and South America. Their morphology is almost identical to members of caeciliidae, sharing their ramming skulls, oral placement and lack of tail. However, siphonopidae is more accurately classed a sister-family to dermophiidae.

#### Dermophiidae

Dermophiidae is the sister-family to siphonopidae. Dermophiids are also classed as common caecilians however, in addition to their range in Central and South America, can also be found in African areas. They are unique among caecilians in that they are not oviparous and instead birth live young, in a similar fashion to mammals.

## Sources

* Caecilians | Wikipedia - https://en.wikipedia.org/wiki/Caecilian
* Rhinatrematidae | Wikipedia - https://en.wikipedia.org/wiki/rhinatrematidae
* Icthyophiidae | Wikipedia - https://en.wikipedia.org/wiki/Ichthyophiidae
* Scolecomorphidae | Wikipedia - https://en.wikipedia.org/wiki/scolecomorphidae
* Herpelidae | Wikipedia - https://en.wikipedia.org/wiki/Herpelidae
* Chikilidae | Wikipedia - https://en.wikipedia.org/wiki/chikilidae
* Caecilidae | Wikipedia - https://en.wikipedia.org/wiki/caeciliidae
* Typhlonectidae | Wikipedia - https://en.wikipedia.org/wiki/Typhlonectidae
* Grandisoniidae | Wikipedia - https://en.wikipedia.org/wiki/grandisoniidae
* Siphonopidae | Wikipedia - https://en.wikipedia.org/wiki/siphonopidae
* Dermophiidae | Wikipedia - https://en.wikipedia.org/wiki/dermophiidae