Gymnophiona - caecilians

The caecilians are a group of limbless, burrowing amphibians, which superficially resemble earthworms or some limbless lizards (snakes, amphisbaenians). Together, caecilians form the order Gymnophiona - one of the three extant amphibian orders, along with Anura (frogs and toads) and Caudata (newts and salamanders).

Diversity and Lower Taxonomy:

The Gymnophiona currently comprises 183 extant species of caecilian. Until recently, these were grouped between the following six families: Caecilidae, Ichthyophiidae, Rhinatrematidae, Scolecomorphidae, Typhlonectidae, and Uraeotyphlidae. However, in 2006, Frost et al. revised amphibian phylogeny, proposing that only three of the previous six caecilian familial groupings - Caecilidae, Ichthyophiidae, and Rhinatrematidae - represented distinct families. The remaining three groupings are now thought to be embedded within these three major lineages, with caecilian taxonomy as follows:

• Caecilidae - 123 species
  • 21 genera including 104 species
  • Scolecomorphinae (6 species in 2 genera)
  • Typhlonectinae (13 species in 5 genera)
• Ichthyophiidae - 50 species in 3 genera (including the genus Uraeotyphlus)
• Rhinatrematidae - 10 species in 2 genera

Distribution and Habitat:

Most caecilians inhabit moist tropical and subtropical regions of South and Central America, South and Southeast Asia, and Sub-Saharan Africa. A single species inhabits Trinidad & Tobago.

Almost all caecilians are terrestrial, but they are elusive as they spend the majority of their lives underground. They burrow primarily in forests, but also in grassland, savanna, shrubland, and wetlands.

Members of the suborder Typhlonectinae are known as aquatic caecilians, and inhabit freshwater systems. At least four typhlonectin species are exclusively aquatic.

Conservation Status (IUCN):

Of the 172 species of caecilian present on the IUCN Red List, over 66% (114 species) are lacking enough data to have their extinction threat assessed (Data Deficient).

For the 58 species for which there is sufficient data for assessment, 52 are considered ofLeast Concern. The remaining 6 species are threatened with extinction, with fourVulnerable, one Endangered (Grandisonia brevis), and one Critically Endangered(Boulengerula niedeni).

Features:

• No appendicular skeleton - they are completely limbless and have no shoulder girdle, but there is a kink in the spine where the pelvic girdle once was.

• 95-285 presacral vertebrae (those anterior to the sacral vertebrae, which once fused with the pelvic girdle).

• Compound, akinetic skull formed of joined plates of bone - this is an excellent and typical adaptation for a fossorial animal (also seen in burrowing lizards, and burrowing mammals, such as the golden moles), allowing the head to be used like a spade to dig, push, and pack earth when burrowing in underground tunnels.

• Reduced eyes.

• 200+ lymph hearts situated intersegmentally under the skin.