The family Caeciliidae (the “common caecilians”) branched off from the rest of the amphibian tree over 160 million years ago in the upper Jurrasic period when dinosaurs were still abundant in the earth’s terrestrial ecosystems. The genus Boulengerula diverged within this family almost 100 million years ago in the late Cretaceous period, and there are now just seven described species in this genus, which is referred to as the “African caecilians” or “Boulenger's Caecilians”, all present in East and Central Africa. This means they diverged from their closest relative at the same time as the divergence of the ancestors of humans and elephants!
Evolutionary Distinctiveness
Order: Gymnophiona
Family: Caeciliidae
The modern caecilians, with their limbless worm-like bodies, are perhaps the most unusual amphibians in appearance, and their behaviour can be equally strange. The order Gymnophiona (the caecilians) is thought to have diverged from other amphibian lineages about 370 million years ago in the Devonian period, over 150 million years before the first mammal.
The earliest caecilian is known from the early Jurassic period in Arizona, U.S.A. 190 million years ago and was named Eocaecilia micropodia because it had very small legs and feet. It also had well-developed eyes, suggesting that it was not an entirely subterranean species and may have had more in common with the salamanders than with the modern caecilians that became its descendents. Modern caecilians therefore underwent major changes in their evolutionary history as they developed elongated bodies and much-reduced eyes, and lost their limbs and latterly their tails.
Carl Linnaeus (the founder of modern taxonomy) described the first species of caecilian (Caecilia tentaculata) in 1758 and initially thought they were related to snakes. The taxonomic order name “Gymnophiona” is actually derived from the Greek words gymnos (meaning naked) and ophis (meaning snake). The caecilians where therefore originally referred to as “naked snakes” because they lack true scales covering their entire body and the first scientific efforts to classify them could not conceive that they were instead closely related to frogs and salamanders.
The family Caeciliidae (the “common caecilians”) branched off from the rest of the amphibian tree over 160 million years ago in the upper Jurrasic period when dinosaurs were dominating the earth’s terrestrial ecosystems. The genus Boulengerula diverged within this family almost 100 million years ago in the late Cretaceous period, and there are now just seven described species in this genus, which is referred to as the “African caecilians” or “Boulenger's Caecilians”, all present in East and Central Africa. This means they diverged from their closest relative at the same time as the divergence of the ancestors of humans and elephants!
Description
This species, like most caecilians, resembles a large earthworm. The body of this species is adapted for burrowing. The species has a bony skull which it uses to push through the soil, and the skin is very tough, the underlying skin layers being fused to the bones to stop them from shearing away during digging. The outer layers of the skin are also strengthened with keratin, which is the same material that forms our hair and fingernails.
Caecilians also have very reduced eyes, which are not visible because they are covered by a layer of bone and a protective - there is not even a conspicuous depression or elevation in the region where the eyes would be expected to lie. However, even though the eyes are covered by a layer of skin and bone, the species are still capable of simple dark-light perception. They possess retractable tactile tentacle sensors located either side of the head between the nostril and the place where their eyes should be found. The tentacles are short and globular, and emanate from small, circular holes.
Ecology
No information is available on the ecology of this caecilian, however it is assumed to be fossorial (burrowing) and to breed like other members of the genus by direct development, where the young emerge as small adults from the egg and there is no larval stage.
Habitat
The only individual collected was found in a small patch of primary montane forest, a fragment outlying the Nyungwe Forest 20km northeast of the collection locality.
Distribution
The single known individual was collected in Cyangugu Prefecture, Rwanda, at 2,000 metres above sea level. The distribution of the species is not known.
Population Estimate
There is no information on the population status of this species; only one specimen is known.
Population Trend
Unknown.
Status
This species is listed on the IUCN Red List of Threatened Species as Data Deficient, as only one individual has ever been collected.
Threats
Due to the fact that only one individual has ever been found, and that the distribution of this species is unknown, it is not possible to assess threats to this caecilian.
Conservation Underway
This species possibly occurs in the Nyungwe Forest Reserve, which may offer some protection, although its presence here has not been confirmed.
Conservation Proposed
Further research into this caecilian is required, including field studies exploring the species’ distribution, population monitoring, ecology, and habitat requirements.
Links
AmphibiaWeb
Global Amphibian Assessment
References
AmphibiaWeb: Information on amphibian biology and conservation [web application]. 2006. Berkeley, California: AmphibiaWeb. Available: . Accessed: 08 December 2006.
Frost, Darrel R. 2006. Amphibian Species of the World: an Online Reference. Version 4 (17 August 2006). Electronic Database accessible at: . American Museum of Natural History, New York, USA.
Halliday, T. and Adler, C. (eds.). 2002. The new encyclopedia of reptiles and amphibians. Oxford University Press, Oxford.
IUCN, Conservation International and NatureServe. 2006. Global Amphibian Assessment. . Accessed on 08 December 2006.
Obst, F.J., Richter, K. and Jacob, U. 1984. The Completely Illustrated Atlas of Reptiles and Amphibians for the Terrarium. T.F.H. Publication Inc., N.J., U.S.A
www.edgeofexistence.org/amphibians/species_info.php?id=1354
