Order - Gymnophiona (Caecilians)

Caecilians are limbless slender amphibians that resemble earthworms. Most are fossorial and live in moist soils close to streams, lakes and swamps. Few are aquatic. They are rarely seen due to their nocturnal behaviour and secretive nature. They have blunt bullet shaped heads and cylindrical limbless bodies with short tails. Bodies are segmented by grooves (primary grooves). Blunt heads are used for burrowing in to soil and they move by serpentine movement. Their eggs are fertilised inside the females body and males have a copulatory organ (phallodeum) to transfer sperms to the female's reproductive tract. Offspring may develop internally or externally. Minute scales (Dermal scales) are present in the skin. Their eyes are vestigial and lie beneath the skin or skull bones. They lack external ear openings. A short retractile sensory tentacle is present on each side of the head between eye and the nostril. The sensory tentacle is used to locate prey. Caecilians occur in the tropics worldwide except Papua-Australia. Approximately 200 species in ten families (Caecilidae, Chikilidae, Dermophiidae, Herpelidae, Ichthyophiidae, Rhinatrematidae, Scolecomorphidae, Siphonopidae, Typhlonectidae, Uraeotyphlidae) are known (Wilkinson et al., 2011; Kamei et al., 2012). Sri Lanka is represented by only family Ichthyophiidae.

Family- Ichthyophiidae (Asian Tailed Caeclians)

The family consists of +55 species that belong to two genera: Ichthyophis and Uraeotyphlus. The members of this family are distributed in India, Sri Lanka and Southeast Asia. Their primary annuli are divided by secondary and tertiary grooves. The body ends in a short true tail. The eyes are visible externally and lie in bony sockets beneath the skin. Their sensory tentacles lie between the eye and the nostril. The reproduction is indirect, i.e they have an aquatic larval stage.

Caecilians of Sri Lanka

Three species of caecilians that belong to the genus Ichthyophis are known from Sri Lanka. Further a cryptic fourth species has been recently discovered through DNA analysis (Gower et al., 2005). But this fourth species has not been formally described. All three species of Ichthyophis are endemic to the island. They are restricted to the wet and intermediate zones of Sri Lanka.

Species of Ichthyophis Fitzinger, 1826 in Sri Lanka

Ichthyophis glutinosus Linnaeus, 1758^E
Ichthyophis pseudangularis Taylor, 1965^E
Ichthyophis orthoplicatus Taylor, 1965^E

Both I. glutinosus and I. pseudangularis possess a yellow lateral stripe along their bodies but I. orthoplicatus lacks a yellow lateral stripe along the body. Ichthyophis glutinosus can be distinguished from I. pseudangularis by the presence of 329-415 annuli rings on body (vs 269-304 in I. pseudangularis). These caecilians are known to feed on earthworms and fossorial insect larvae. They deposit their eggs in burrows close to a waterbody. When the eggs hatch, small gilled eel like larvae wriggle overland to water to complete their metamorphosis (Breckenridge & Jayasinghe, 1979; Breckenridge et al., 1987).

Abbreviations in superscript

E- Endemic Species, Ex- Extinct species, Cr- Critically Endangered Species

References

Breckenridge, W.R., Jayasinghe, S. (1979) Observations on the eggs and larvae of Ichthyophis glutinosus. Ceylon Journal of Science (Biological Sciences), 13: 187–204.

Breckenridge, W.R., Nathanael, S., Pereira, L. (1987) Some aspects of the biology and development of Ichthyophis glutinosus (Amphibia: Gymnophiona). Journal of Zoology, 211: 437–450.

Gower, D.J., Bahir, M.M., Mapatuna, Y., Pethiyagoda, R., Raheem, D., Wilkinson, M. (2005) Molecular phylogenetics of Sri Lankan Ichthyophis (Amphibia: Gymnophiona: Ichthyophiidae), with a discovery of a cryptic species. Raffles Bulletin of Zoology, 12: 153-161.

Kamei, R. G., San Mauro, D., Gower, D.J., Van Bocxlaer, I., Sherratt, E., Thomas, A., Babu, S., Bossuyt, F., Wilkinson, M., Biju, S.D. (2012). Discovery of a new family of amphibians from northeast India with ancient links to Africa. Proceedings of the Royal Society B, 279: 2396–2401.

Wilkinson, M., San Mauro, D., Sherratt, E., and Gower, D.J. (2011) A nine-family classification of caecilians (Amphibia: Gymnophiona). Zootaxa, 2874: 41-64.