TAILLESS CAECILIANS: Caeciliidae

PHYSICAL CHARACTERISTICS

Tailless caecilians (sih-SILL-yuhns) are small to very large caecilians that have a very short tail or no true tail. These caecilians are 4 to 63 inches (10 to 160 centimeters) long. Some tailless caecilians live on land, and some live only in water. Tailless caecilians have a flat head. The mouth opens on the bottom of the head because the upper jaw is longer than the lower jaw. The eyes are covered by skin or, in some species, by both skin and bone. The tentacles lie between the eyes and the nostrils.

Caecilians look like earthworms. A series of rings runs the length of the body starting just behind the head. The rings are inside the body and attached to the vertebrae (VER-teh-bree), or the bones that make up the spinal column. Tailless caecilians have one ring per vertebra (VER-teh-bruh, the singular of vertebrae). The skin is folded over the rings, making grooves between the rings.

GEOGRAPHIC RANGE

Tailless caecilians live in Central and South America; the eastern and western parts of Africa, but not the Sahara; the Seychelles; India; Sri Lanka; the Philippines; and the region that extends from southern China through the Malay Peninsula.

HABITAT

Tailless caecilians live in tropical forests and grasslands and on stream banks. Land-dwelling tailless caecilians live in loose, moist, soil rich in decayed plant matter and leaf litter. They are often found under rocks, logs, and waste material, such as piles of coffee hulls. Many of these caecilians are found near streams. Some tailless caecilians live in grassland, and scientists find them by rolling the grass layer away from the soil. Tailless caecilians that live in water for part or all of their life cycle live on the banks of streams and rivers and sometimes travel onto nearby land or farther out into slow-moving water. Water-dwelling tailless caecilians hide under hanging branches, logs, and other floating objects.

DIET

Tailless caecilians are sit-and-wait predators, staying in their burrows or on the ground and then grabbing prey animals that wander near them. These caecilians eat earthworms, termites, other small invertebrates, and even small lizards and rodents. Invertebrates (in-VER-teh-brehts) are animals without backbones. Tailless caecilians lunge at their prey, grabbing it with their strong jaws and powerful jaw muscles. They force prey animals into their mouths and gradually swallow them. Some tailless caecilians move backward into their burrows, turning rapidly on their body in a corkscrew motion in order to break the prey into bite-sized morsels. Water-dwelling tailless caecilians hunt for their prey by poking around with their snout at the bottom of the stream.

BEHAVIOR AND REPRODUCTION

Little is known about the behavior of land-dwelling tailless caecilians because of their secretive, soil-dwelling nature. Some of these animals emerge from deep in the soil or leaf litter to look for food at dusk or dawn, often during light rain. Tailless caecilians are expert burrowers, digging head-first through moist soil that is rich in decayed plant matter. Species may differ in their ability to burrow efficiently in different kinds of soils. Tailless caecilians appear to spend most of their time in their burrows, but they also can travel quite far from their burrows. Scientists know little about the behavior of the water-dwelling and partially water-dwelling tailless caecilians because these animals typically live in slow-moving streams and rivers that have a lot of plant material that obstructs the view of the animals.

At mating time a male tailless caecilian inserts sperm directly into the female's reproductive tract. Scientists have observed tailless caecilians in aquariums coiling around each other before the male places the sperm in the female. The eggs are fertilized (FUR-teh-lyzed), or joined with sperm, inside the female's body.

Tailless caecilians use several methods of reproduction. Some species lay eggs that hatch into free-living larvae. Larvae (LAR-vee) are animals in an early stage that change body form in a process called metamorphosis (MEH-tuh-MORE-feh-sis) before becoming adults. Some species lay eggs on land, and the larvae develop and go through metamorphosis before hatching, so that when they hatch they have the body form of adults. In some species the young develop in the egg ducts of the female, eating nutrient liquid made by the egg ducts. These young also are born with the body form of small adults. The females of some species of tailless caecilians take care of their eggs by coiling their bodies around the cluster of eggs. They also take care of newly hatched young.

TAILLESS CAECILIANS AND PEOPLE

Tailless caecilians help to control damaging insects, such as termites. Because they actively burrow, rather than following root channels or other ready-made holes in the ground, tailless caecilians aid in turning the soil and maintaining good soil condition. In some parts of the world, people think caecilians are nasty, dangerous animals. In other places, however, people eat them. Some people keep tailless caecilians as pets in aquariums.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists one species of tailless caecilians as Endangered and one species as Vulnerable. Endangered means facing very high risk of extinction in the wild. Vulnerable means facing high risk of extinction in the wild. Changes in land use are restricting the geographic ranges of tailless caecilians, and some populations get a fungus disease.

MEXICAN CAECILIAN (Dermophis mexicanus): SPECIES ACCOUNTS

Physical characteristics: Mexican caecilians are 12 to 20 inches (30 to 50 centimeters) long and have a thick body. They are dark gray with paler markings on the belly, jaw, and tentacles. The grooves between the rings are darker than the main body color.

Geographic range: Mexican caecilians live in an area that extends from the lowlands and mountains of central Mexico south to northern Panama.

Habitat: Mexican caecilians live in moist soil that breaks up easily and in leaf litter.

Diet: Mexican caecilians are sit-and-wait predators. They eat invertebrates and vertebrates (VER-teh-brehts), or animals with a backbone, that live or travel in soil or leaf litter, including earthworms, termites, insects such as crickets that have shed their outer layer, and even small lizards and baby mice.

Behavior and reproduction: Mexican caecilians spend most of their time in burrows in loose, moist soil. They often come out at dusk in a light rain to look for food on the surface. These caecilians make their own burrows in many kinds of soil rather than using the burrows of other animals. Mexican caecilians move with an accordion-like motion and with side-to-side, wavy movements.

Mexican caecilians give birth to fully developed young. They are ready to reproduce when they are two to three years old. The male places the rear part of his cloaca into the cloaca of the female and transfers sperm directly to her reproductive tract. The cloaca (kloh-AY-kuh) is the chamber in some animals that holds waste from the kidneys and intestines, holds eggs or sperm about to be released to the outside, holds sperm entering a female's body, and is the passage through which young are born. Fertilization (FUR-teh-lih-ZAY-shun), or the joining of egg and sperm to start development, takes place inside the female.

Male Mexican caecilians make sperm eleven months of the year, but all females give birth at about the same time, in May and June when the rainy season begins. The young take eleven months to develop. Inside the female the developing young use up the yolk supply of their eggs about three months into the development period. The mother then releases a nutrient liquid from glands lining her egg ducts. The developing young move around in the egg ducts, eating the liquid. They have special teeth that they use to stimulate release of the nutrient liquid and to help take it into their mouths. These teeth are shed at birth, and the adult teeth, which are very different from those of the young inside the mother, grow out within a few days. The developing young have gills that have three branches, and each of the three branches has many more branches. The developing young use the gills and their skin to breathe while in the egg ducts. Gills are organs for obtaining oxygen from water.

Female Mexican caecilians give birth to three to sixteen young, which are 4 to 6 inches (10 to 15 centimeters) long at birth. These young are quite large considering the mother is only 12 to 18 inches (30 to 45 centimeters) long.

Mexican caecilians and people: Mexican caecilians are valuable to humans. They turn soil as they make their burrows, and they eat insects, such as termites, that can be harmful to people or their property.

Conservation status: Mexican caecilians are not considered threatened or endangered. Their numbers are high in some areas, but their habitat is being changed as trees are cut down to make way for farming. Mexican caecilians seem to adapt to some kinds of farm use. For example, there are large numbers of tailless caecilians on coffee farms, where the coffee hulls are thrown in piles to decay, thus forming the moist organic soil that is best for Mexican caecilians and their earthworm prey. ∎

CAYENNE CAECILIAN (Typhlonectes compressicauda): SPECIES ACCOUNTS

Physical characteristics: Cayenne (kye-EHN) caecilians are water dwellers. They have a fin on the back that runs the length of the body. The body is flat from side to side, making the caecilians look more like eels than earthworms. These caecilians have large passages inside the head between the nose and the roof of the mouth, and they have well-developed lungs. Cayenne caecilians have one ring per vertebra, and the grooves between the rings are deep. These caecilians are gray to dark blue or black. Adults are 12 to 22 inches (30 to 55 centimeters) long. The cloaca region is flat, forming a disk that is paler in color than the rest of the body.

Geographic range: Cayenne caecilians live throughout the Guianas and the Amazon region of South America.

Habitat: Cayenne caecilians live in slow-moving, warm tropical rivers and streams.

Diet: Cayenne caecilians root around in the mud of the sides and bottoms of the waterways in which they live. They eat shrimp, insect larvae, and small fish. These caecilians have a strong bite mechanism. In captivity cayenne caecilians feed on pieces of earthworms and liver. Cayenne caecilians seem to sense the presence of prey by touch or motion.

Behavior and reproduction: Cayenne caecilians share burrows with one another and leave the burrows at sunset to look for food. These animals have mucus glands all over their bodies. The mucus is poisonous and tastes bad to fish. Predators of cayenne caecilians include large fish, snakes, and birds.

Cayenne caecilians mate by nudging and coiling around each other. The male places sperm in the female, and fertilization takes place inside her body. Cayenne caecilians give birth to fully developed young, which are born seven to nine months after fertilization. A female can give birth to six to fourteen young at a time. The developing young have gills that are shed soon after birth. The developing young have teeth they use to eat a nutrient liquid made by the female's egg ducts. These teeth also are shed soon after birth, and then the adult teeth grow in.

Cayenne caecilians and people: Cayenne caecilians are sold in aquarium stores as rubber eels or black eels. Only rarely do store owners identify them as amphibians (am-FIB-ee-uhns), which are vertebrates (VER-teh-brehts), or animals with a backbone, that have moist, smooth skin; are cold-blooded, meaning their body temperature is the same as the temperature of their surroundings; and, in many instances, but not in the case of cayenne caecilians, have a two-stage life cycle.

Conservation status: Cayenne caecilians are not considered threatened or endangered. They have been collected extensively by fishermen, scientists, and pet dealers. ∎

FOR MORE INFORMATION

Books:

Duellman, William E., and Linda Trueb. Biology of Amphibians. Baltimore, MD: Johns Hopkins University Press, 1994.

Lamar, William W. The World's Most Spectacular Reptiles and Amphibians. Tampa, FL: World, 1997.

Lawlor, Elizabeth P. Discover Nature in Water and Wetlands. Mechanicsburg, PA: Stackpole, 2000.

Llamas Ruiz, Andres. Reptiles and Amphibians: Birth and Growth. New York: Sterling, 1996.

Petranka, J. W. Salamanders of the United States and Canada. Washington, DC: Smithsonian Institution Press, 1998.

Web sites:

"Caecilian." Animal Bytes.http://www.sandiegozoo.org/animalbytes/t-caecilian.html (accessed on April 11, 2005).

Hawes, Alex. "On Waterdogs, Mudpuppies, and the Occasional Hellbender." Zoogoer.http://nationalzoo.si.edu/Publications/ZooGoer/2000/2/waterdogsmudpuppieshellbender.cfm (accessed on April 11, 2005).

Summers, Adam. "Squeeze Play." Natural History.http://biomechanics.bio.uci.edu/_html/nh_biomech/caecilian/caecilian.htm (accessed on April 11, 2005).