Caelians are limbless amphibians that resembles 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 primary grooves. Blunt heads are used for digging. Their movement is serpentine. Their fertilisation is internal and males have a copulatory organ (phallodeum). Offspring may develop internally or externally. 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 nostrill. The sensory tentacle is used to identify prey. Caecilians occur in the tropics worldwide except Papua-Australia. Approximately 160 species in seven families (Caecilidae, Icthyophidae, Rhinatrematidae, Scolecomorphidae, Typhlonectidae, Uraeotyphlidae) are known. Sri Lanka is represented by only family Icthyophiidae.
Family- Ichthyophiidae (Asian Tailed Caeclians)
The family consisits of +35 species that belong to two genera: Caudacaecilia and Ichthyophis. 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 family Ichthyophiidae are known from Sri Lanka. Further a cryptic fourth species has been recently discovered through DNA analysis. But this fourth species has not been formally described. All three species of caecilians known from Sri Lanka belongs to the genus Ichthyophis and all of them are endemic to the island. They are restricted to the wet and intermediate zones of Sri Lanka. The three species are Ichthyophis glutinosus, Ichthyophis pseudangularis and Ichthyophis orthoplicatus. 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. 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.
Species of Ichthyophis Fitzinger, 1826 in Sri Lanka
Ichthyophis glutinosus Linnaeus, 1758E
Ichthyophis pseudangularis Taylor, 1965E
Ichthyophis orthoplicatus Taylor, 1965E
Abreviations in superscript
E- Endemic Species, Ex- Extinct species, Cr- Critically Endangered Species