Bio Facts: Caecilian, Rio Cauca
Rio Cauca Caecilian
Gymnophiona Sub-order: Lissamphibia
The drainage systems of the Cauca and Magdalena rivers in western and northern Colombia to the general vicinity of Lake Maracaibo Basin in Venezuela. It occurs up to 3,280 ft (1,000m) above sea level. Suggestions of its occurrence in the Orinoco River, and from Trinidad require confirmation.
Aquatic species, living in rivers, marshes and lakes, usually in open areas, and is only rarely found on land.
T. natans grow to 45 cm (17.7 inches) to 55 cm (21.7 inches) in length. They are dark grey- black in color. The most distinguishing characteristic of all caecilians is their limbless, worm-like bodies.
In the wild, caecilians eat worms, caterpillars, termites, and small burrowing snakes.
IUCN – Least concern; CITES – Not listed
Caecilian behavior is not well known. They are not a well-studied order due to difficulty of finding them in their well-hidden burrows. They are thought to be solitary, coming together to mate but courtship rites and estrus cycles are also not known. The young are also thought to be rather precocial when born, with the mother not caring for them after birth. They stay underground until heavy rains drive them to the surface, presumably to avoid drowning.
While T. natans can and occasionally does breathe air at the surface, most of the respiration takes place through its skin.
The species is ovoviviparous, giving birth to young in water. The gestation period lasts app. 220 days. 3-7 live, fully developed young are born, which after only one year reach almost half the size of an adult at just under 10 inches (25 cm).
Inside the skin are calcite scales. Because of these scales, the caecilians were once thought to be related to the fossil Stegocephalia, but they are now believed to be a secondary development, and the two groups are most likely unrelated.
The skin also has numerous ring-shaped folds, or annuli, that partially encircle the body, giving them a segmented appearance. Like other living amphibians, the skin contains glands that secrete a toxin to discourage predators. The skin secretions of Siphonops paulensis have been shown to have hemolytic properties.
Caecilian anatomy is highly adapted for a burrowing lifestyle. They have a strong skull, with a pointed snout used to force their way through soil or mud. In most species, the number of bones in the skull are reduced and fused together, and the mouth is recessed under the head. Their muscles are adapted to pushing their way through the ground, with the skeleton and deep muscles acting as a piston inside the skin and outer muscles. This allows the animal to anchor its hind end in position, and force the head forwards, and then pull the rest of the body up to reach it in waves. In water or very loose mud, caecilians instead swim in an eel-like fashion. Caecilians in the family Typhlonectidae are aquatic as well as being the largest of their kind. The representatives of this family have a fleshy fin running along the rear section of their body, which enhanced propulsion in water.
All but the most primitive caecilians have two sets of muscles for closing the jaw, compared with the single pair found in all other vertebrates. These are more highly developed in the most efficient burrowers among the caecilians, and appear to help keep the skull and jaw rigid.
Owing to their underground life, the eyes are small and covered by skin for protection, which has led to the misconception that they are blind. This is not strictly true, although their sight is limited to simple dark-light perception. All caecilians possess a pair of tentacles, located between their eyes and nostrils. These are probably used for a second olfactory capability, in addition to the normal sense of smell based in the nose.
Except for one lungless species — Atretochoana eiselti, only known from two specimens collected in South America — all caecilians have lungs, but also use the skin or the mouth for oxygen absorption. Often the left lung is much smaller than the right one, an adaptation to body shape that is also found in snakes.
Caecilians are the only order of amphibians which only use internal insemination. Male caecilians have a penis-like organ, the phallodeum, which is inserted into the cloaca of the female for 2 to 3 hours. About 25% of the species are oviparous (egg-laying); the eggs are guarded by the female. For some species the young caecilians are already metamorphosed when they hatch; others hatch as larvae. The larvae are not fully aquatic, but spend the daytime in the soil near the water.
75% of the species are viviparous, meaning that they give birth to already developed offspring. The fetus is fed inside the female with cells of the oviduct, which they eat with special scraping teeth.
The egg laying species Boulengerula taitanus feeds its young by developing an outer layer of skin, high in fat and other nutrients, which the young peel off with similar teeth. This allows them to grow by up to ten times their own weight in a week. The skin is consumed every three days, the time it takes for a new layer to grow, and the young have only been observed to eat it at night. It was previously thought that the juveniles subsisted on a liquid secretion from their mother.
Some larvae, such as those of Typhlonectes, are born with enormous external gills which are shed almost immediately. Ichthyophis is oviparous and known to show maternal care, with the mother guarding the eggs until they hatch.
The name ‘caecilian’ derives from the Latin word caecus = blind, referring to the small or sometimes non-existing eyes. The name dates back to the taxonomic name of the first species described by Carolus Linnaeus, which he gave the name Caecilia tentaculata. The taxonomic name of the order derives from the Greek words γυμνος (gymnos, naked) and οφις (ophis, snake), as the caecilians were originally thought to be related to snakes.
Taxonomically the caecilians are divided into 6 families. It is almost certain that not all species have been described yet, and that some of the species described already may be combined into one species in future reclassifications.
Rio Cauca caecilians are members of an ancient family of amphibians. These unique animals went underground long before the dinosaurs appeared (all caecilians are constructed for digging). They are nearly blind and find their food by taste and smell.
It has been thought that Caecilians were the sister group of the other lissamphibians, the frogs and salamanders. Molecular data, however, places them to closer to salamanders than to frogs. It was also commonly believed that all amphibians are descended from the fossil amphibians, the Temnospondyls. It is now being suggested that only frogs are descended from the Temnospondyls and salamanders and caecilians descended from the Microsaurs. This is still highly controversial as it is contradicted by traditional morphology.
IUCN listed as Least Concern in view of its wide distribution, tolerance of significant habitat degradation, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category. It is extremely resilient to habitat degradation and pollution, both of which are extensive within its range. It is popular in the international pet trade, but not at a level to constitute a threat to the species.
Jacksonville Zoo History:
The Rio Cauca caecilian first arrived at the Jacksonville Zoo in 2003.