Tailless caecilians

(Caeciliidae)

Class Amphibia

Order Gymnophiona

Family Caeciliidae

Thumbnail description
Miniaturized to very large caecilians, mostly lacking a tail, with relatively few body rings

Size
4–63 in (10–160 cm)

Number of genera, species
26 genera, 107 species

Habitat
Tropical forests, grasslands, streambanks

Conservation status
Not classified by the IUCN, but several species are declining and some are thought to be extinct

Distribution
Virtually pantropical; Central and South America, East and West Africa, the Seychelles Islands, India and Sri Lanka, Southeast Asia from the East Indies to southern Philippines, southern China through the Malay Peninsula

Evolution and systematics

The phylogenetic relationships of members of the family Caeciliidae are not well known. Various phylogenetic hypotheses have appeared in the literature, some based on morphological data and some on biochemical or molecular data. Because of either methodological problems or the sampling of very few taxa (especially with biochemical or molecular data), most recently advanced hypotheses have been rejected by experts on caecilian biology. These experts are working toward assembling more complete data sets in order to fully analyze the relationships of the members of the family. It is clear, though, that the three genera found on the Seychelles Islands form a distinct lineage. Their relationship to other caecilians, and of the African, Indian, and American caeciliids to each other, are not yet resolved.

Several classification issues exist for the family Caeciliidae. Both morphological and molecular data suggest that the family is multiply paraphyletic; that is, that some groups have members that occur not as monophyletic clades, but within other clades. A particular problem is that of the semi-aquatic to aquatic caecilians of northern, central, and western South America, long recognized as a separate family, the Typhlonectidae. The features that distinguish them are particular to that group, so they do not provide information about relationships. They share some morphological and molecular characters with certain genera placed in the family Caeciliidae. Therefore, taxonomic purists refer to the typhlonectids as a subfamily of the caeciliids, rather than a separate family. This account follows that purism, with some hesitation, because most experts on caecilians reject that conclusion. They continue to recognize the family Typhlonectidae, because they are convinced that adequate data will reveal that the current family Caeciliidae is composed of several lineages that are likely to be designated new families. In the absence of those data, this account includes the aquatic lineage as a subfamily, the Typhlonectinae, of the Caeciliidae. The subfamily name Caeciliinae has been proposed for some of the remaining taxa; it is not appropriate to all the remaining genera, thus posing a taxonomic inequity of names. Other subfamilies have been proposed but rejected on methodological grounds. The data necessary to resolve these issues are steadily accruing, so in the near future, we should have a much better understanding of the phylogenetic relationships within the Caeciliidae and of the family with other caecilians.

Physical characteristics

Caeciliids have the features typical of most caecilians—elongate limbless bodies, very short to no true tail, the head flattened with the mouth underslung. The eyes are covered by skin, or in some species, by skin and by bone. The chemosensory/tactile tentacle lies between the eye and the nostril. Perhaps the most striking feature of caecilians is the series of rings around the body. All caeciliids have such rings, but many have a primary series that runs the length of the body, and a secondary series that can be as long as the primary series, to only a few rings posteriorly, to complete loss of the secondary series.

Distribution

This family is virtually pantropical in its distribution. Its range includes Central and South America; East and West Africa; the Seychelles Islands; India and Sri Lanka; Southeast Asia from the East Indies to southern Philippines; and southern China through the Malay Peninsula.

Habitat

Terrestrial caeciliids live in habitats characterized by loose, moist, organically rich soil and leaf litter. They are often found under stones, logs, and debris, such as piles of coffee hulls. Many species are found near streams. Some species occur in savanna areas and are found by rolling the grass layer from the soil. The semiaquatic to aquatic typhlonectives live in the banks of streams and rivers and variously venture onto nearby land or out into the bodies of slow-moving waters. They hide under hanging branches, logs, and other floating materials.

Behavior

Little is known about the behavior of terrestrial caeciliids because of their secretive, soil-dwelling nature. Members of several species are known to emerge from deeper in the soil or leaf litter to forage at dusk or dawn, often during light rain. They appear to be capable burrowers, digging head-first through moist organic soil. Species may differ in their ability to burrow efficiently in different kinds of soils. They appear to spend most of their time in their burrows, but they are capable of considerable movement as well. There also is limited information on the behavior of the semiaquatic to aquatic typhlonectines, except for some laboratory observations, because they typically live in rather slow-moving streams and rivers that have a lot of organic material in the water, thus making observation difficult in the field.

Feeding ecology and diet

Caeciliids are "sit-and-wait" predators, staying in their burrows or on the substrate surface where they seize prey items that wander near them. They are carnivores, eating earthworms, termites, a diversity of other small invertebrates, and even small lizards and rodents. They lunge at their prey, grabbing it with their strong jaws and powerful jaw muscles. They propel prey items into their mouths and progressively swallow them. Several species have been observed to retreat backward into their burrows, turning rapidly on their body axis in a corkscrew motion, so that the prey item may be sheared to a bite-sized morsel.

Reproductive biology

Caeciliids include several modes of reproduction: egglaying with free-living larvae; egg-laying with direct development (the eggs laid on land, and development through metamorphosis occurs before hatching, so that there is no free-living larval stage); and viviparity (retention of the developing embryos in the oviducts of the mother, provision of nutrient material in the oviducts, and birth of fully metamorphosed juveniles). All caeciliids apparently have internal fertilization (as it is assumed is characteristic of all caecilians); the male inserts a cloacal intromittent organ into the vent of the female so that sperm is transported directly to her reproductive tract. Courtship and mating are not reported in the literature, save for that of typhlonectines. They have been observed in aquaria to coil around each other before the male inserts his intromittent organ. It is not known how males and females recognize each other, though pheromones have been suggested for Typhlonectes. Some species of caeciliids are known to provide care of either their laid eggs (Idiocranium russeli females curl their bodies around the clutch) or their altricial young (Siphonops annulatus and Geotrypetes seraphini). Idiocranium, Boulengerula, Hypogeophis, some Grandisonia, and perhaps some Caecilia and Oscaecilia have direct development, so that juveniles hatch; Siphonops annulatus also may have direct development, but its newly hatched young apparently feed on skin secretions of the mother, as do the newborns of Geotrypetes seraphini. Viviparity has probably evolved at least three times in caecilians, including all of the "typhlonectids," so far as is known, and several caeciliids (e.g., Dermophis, Gymnopis, Geotrypetes), as well as the scolecomorphid genus Scolecomorphus. Gestation periods are lengthy (e.g., seven to nine months in Typhlonectes, 11 months in Dermophis), and young are born fully metamorphosed.

Conservation status

Too little is known of the ecology and biology of nearly all species of caecilians to evaluate their conservation status. However, anecdotal information indicates that land use change is severely restricting the ranges of several species, some populations are succumbing to the chytrid fungus, and some species may be extinct; they have not been collected for some time at localities where they had been observed previously. To date, no species are listed by the IUCN.

Significance to humans

Caecilians are little-appreciated biological control carnivores; they forage on small arthropods and so forth, thus potentially helping to control such populations. Because they actively burrow, rather than following root channels or other ready-made holes in the ground, they aid in turning the soil and maintaining good soil condition. In most areas of the world, the indigenous lore about caeciliids is that they are nasty, dangerous animals; in contrast, however, humans eat them in some parts of Southeast Asia.

Species accounts

List of Species

Mexican caecilian

Dermophis mexicanus

taxonomy

Siphonops mexicanus Duméril and Bibren, 1841, Mexico. Dermophis mexicanus is a member of the Caeciliidae; it has been placed in a subfamily Dermophiinae by some workers, but most experts reject the use of subfamilial designations until generic relationships of caecilians are better understood.

other common names

Spanish: Dos cabezas, solda con solda.

physical characteristics

Adults are medium-length for caecilians (11.8–19.7 in [300–500 mm] total length) and fairly stout bodied. They are dark gray dorsally, with paler venters and jaw and tentacle markings. Their numerous body annuli are more darkly pigmented; this feature distinguishes Dermophis mexicanus from most other species in the genus.

distribution

Mexico, from lowlands and the mountains of Guerrero on the Pacific versant, and Veracruz on the Atlantic, to northern Panama.

habitat

Moist, friable soil; leaf litter.

behavior

Little is known of the behavior of caecilians, including D. mexicanus. They spend most of their time in burrows in loose, moist soil; they often emerge at dusk in a light rain to forage on the surface. They make their own burrows and are effective in a diversity of soil types. The internal concertina and lateral undulation modes of locomotion of D. mexicanus have been analyzed.

feeding ecology and diet

These carnivores are sit-and-wait predators; their diet is composed of invertebrates and certain vertebrates that live or travel on soil or leaf litter and so on, including earthworms, termites, orthopteran instars, even small lizards and baby mice, depending on the size of the predator. Their feeding mechanics have been studied experimentally.

reproductive biology

Dermophis mexicanus is a viviparous species. Nothing is known of mate attraction or courtship. They are sexually mature at two to three years of age. Like all caecilians, Dermophis have internal fertilization; the male inserts the extruded rear part of its cloaca into the cloaca of the female, thus transporting sperm directly to her reproductive tract. Males are spermatogenic 11 months of the year; however, females in a population are in synchrony in the developmental stages of their oviductal embryos and young, and they all give birth at about the same time, in May–June when the rainy season begins. There is no evidence of sperm storage by the females. Their pregnancies are 11 months long. They have three to 16 young, which are born at 3.9–5.9 in (10–15 cm) (the mother is only 11.8–17.7 in

[30–45 cm]). The embryos exhaust the yolk supply of their small eggs (0.1 in [2 mm] diameter) about three months into the gestation period; the mother secretes a nutrient material from the glands of the lining of her oviducts. The developing young move around in the oviducts, ingesting the secretions. The fetuses have a special dentition that they apparently use to stimulate the secretion and to help take it into their mouths. The fetal dentition is shed at birth, and the adult teeth, which are very different in shape and distribution from those of the fetus, erupt within a few days. The fetuses have gills; they have three branches with numerous extensions. The gills and the skin are the organs of gaseous exchange in the oviducts.

conservation status

The species remains locally abundant in some areas, but its habitat is being changed considerably as forests are removed for agriculture. It seems to adapt reasonably well to some kinds of farm use; for example, it has been abundant on some coffee fincas, where the coffee hulls are thrown in piles to decay, thus forming the moist organic soil in which Dermophis and its prey, earthworms, survive well.

significance to humans

Dermophis is valuable to humans; it can turn soil as it makes its burrows and eats insects and the like that might otherwise become super abundant.

Frigate Island caecilian

Hypogeophis rostratus

taxonomy

Coecilia rostrata Cuvier, 1829, Mahé, Seychelles. Hypogeophis, including only one species, is a member of a monophyletic lineage that has radiated on the granitic islands in the Seychelles archipelago. Molecular, morphological, biochemical, and chromosome data all support the monophyly of the Seychelles genera, but do not give clues as to the relationships of the Seychelles caecilians to those of Africa, India, and southeast Asia.

other common names

English: Sharp-nosed caecilian.

physical characteristics

Hypogeophis rostratus is a relatively small (7.9–14.6 in [200–370 mm] total length as adults) caecilian, dark black–brown in coloration, slightly paler ventrally. Its body has the characteristic annuli; it does not have a tail. The head is small and rather pointed, the eyes covered by skin, the mouth underslung, and the chemosensory tentacle apparent on the side of the head. The structure and development of the skull, teeth, and vertebral column and many organs of the body are well known, through the work of the German biologist Harry Marcus during the early part of the twentieth century, and more recent work by Swiss and United States scientists.

distribution

Hypogeophis rostratus is a relatively abundant species, inhabiting all of the granitic islands in the Seychelles group.

habitat

The species occurs in a diversity of habitats, including moist leaf litter and soil, under wood and rocks, in debris piles, and occasionally in streams.

behavior

Little is published about the behavior of the Seychelles caecilians.

feeding ecology and diet

Specific information on the natural diet of Hypogeophis is not available. Presumably they eat earthworms and terrestrial arthropods, as do most caecilians; there are anecdotal reports that they also consume frogs. Hypogeophis in captivity are strong-bite, sit-and-wait predators, suggesting that this is their mode in nature as well, similar to the majority of caecilians.

reproductive biology

Males and females court in streams. Hypogeophis rostratus is a direct developer: females lay internally fertilized eggs in burrows on land and coil around them to guard them. They apparently can breed at any time of year. The eggs are large, approximately 0.3 in (8 mm) diameter. The first cell divisions take place atop the yolk, so that a disk of cells that will become the embryo is formed, similar to birds. The embryos develop inside their egg membranes, have gills and so forth, and then undergo metamorphosis, all before hatching as juvenile caecilians.

conservation status

Hypogeophis rostratus seems to be abundant.

significance to humans

The carnivorous habits make it useful as an insect/arthropod control mechanism, and its burrowing aids in soil turning and aeration.

Cayenne caecilian

Typhlonectes compressicauda

taxonomy

Caecilia compressicauda Duméril and Bibron, 1841, French Guiana. Typhlonectes compressicauda is a member of a group of five genera thought to be closely related because of certain shared, derived characters, mostly associated with semi-aquatic to aquatic habits. The group is recognized as a family by most biologists expert on caecilians, but some phylogenetic analyses place them within the paraphyletic family Caeciliidae. It is difficult to distinguish compressicauda from T. natans; much of the information in the literature purportedly describing T. compressicauda and its biology really pertains to T. natans.

other common names

None known.

physical characteristics

Typhlonectes compressicauda, like most "typhlonectids," lacks secondary body annuli, and its annuli are distinct. Animals are gray to dark blue–black, and nearly uniform in color. Adults are 11.8–21.7 in (300–550 mm) total length. They have moderately long, flattened heads. They also have a slight dorsal "fin" or ridge that extends from the anterior third of the body to its end. The vent (cloacal) region is flattened, forming a disk that is paler in color. Features associated with its aquatic habit include the body fin, lateral body compression, large choanae, and development of both lungs.

distribution

Typhlonectes compressicauda is found throughout the Guianas and the Amazon region; the closely related and very similar T. natans is restricted to Colombia and northwestern Venezuela.

habitat

This caecilian is fully aquatic, inhabiting slow-moving, warm tropical rivers and streams.

behavior

Individuals are known to share burrows and leave them at sunset to forage for food. They have many mucous glands all over their bodies, and the secretion is apparently toxic and distasteful to fishes. Predators include large fish, snakes, and birds. There are several reports in the literature of observation of courtship by nudging and coiling around each other, intromission, and of birth in captivity the ability to view the animals in aquaria has allowed more extensive observation of their feeding, swimming, and reproductive behavior than that of the more secretive terrestrial caecilians. Pheromones have been suggested to be involved in mate attraction.

feeding ecology and diet

The animals root around in the mud of the sides and bottoms of the waterways they inhabit. They eat arthropods of various sorts, including shrimp, insect pupae, and so on, and small fish. They have the strong-bite mechanism typical of caecilians. In captivity, they feed on pieces of earthworms and liver. They do not seem to use chemosensory cues extensively to find food items; they seem to perceive presence of prey by touch or motion.

reproductive biology

Typhlonectes compressicauda is viviparous, as all typhlonectids are suspected to be. The species has a seven to nine month gestation period; a female can have six to 14 developing young, with a mean of 10. The gills of typhlonectid embryos fuse into large sacs. The gills may function in uptake of nutrients as well as gaseous exchange. The gills are shed shortly after birth. The fetal dentition, different in structure and arrangement from that of the adults, is used to ingest oviductal secretions. Fetuses are fully metamorphosed at birth; even their hemoglobin has changed from the embryonic to the adult.

conservation status

This species has been collected extensively, apparently with no indication of diminution of its numbers. It has been taken by fishermen (and scientists) using nets to catch fish. No formal designation of its conservation status has been attempted, but the species apparently remains locally abundant, so far as is known.

significance to humans

The ecological significance of the species has not been determined; presumably its carnivorous habits and abundance make it an effective part of the riverine food web. Many animals have been imported and sold in aquarium stores as rubber eels or black eels; only rarely are they identified as amphibians, and then they are usually called T. compressicauda. In fact, the species that has been most imported is T. natans, so many of the reports in aquarium journals bear an incorrect species name.

Resources

Books

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

Exbrayat, Jean-Marie. Les Gymnophiones Ces curieux Amphibiens. Paris: Societe Nouvelle des Editions Boubee, 2000.

Himstedt, W. Die Blindwuehlen. Marburg: Die Neue Brehm-Buecherei Bd. 630, Westart Wissenschaften and Heidelberg: Spektrum Akademischer Verlag, 1996.

Nussbaum, Ronald A. "Amphibians of the Seychelles." In Biogeography and Ecology of the Seychelles Islands, edited by David R. Stoddart. The Hague, Netherlands, and Boston: W. Junk Publishers (1984): 379–415.

Taylor, Edward H. The Caecilians of the World. Lawrence, KS: University of Kansas Press, 1968.

Periodicals

Brauer, August. "Beitraege zur Kenntniss der Entwicklungsgeschichte und der Anatomie der Gymnophionen. II. Die Entwicklung der auessern Form." Zoologische Jahrbuch der Anatomie 12 (1899): 477–408.

Marcus, Harry, O. Winsauer, and A. Huebner. "Beitrage zur Kenntnis der Gymnophionen. XVIII. Der kinetische Schadel von Hypogeophis und die Gehoerknoekelchen. " Zeit. Anat. Entw. 100 (1933): 149–193.

Moodie, G. E. E. "Observations on the Life History of the Caecilian Typhlonectes compressicaudus (Dumeril and Bibron) in the Amazon Basin." Canadian Journal of Zoology 56 (1978): 1005–1008.

Nussbaum, Ronald A., and Mark Wilkinson. "On the Classification and Phylogeny of Caecilians (Amphibia: Gymnophiona), a Critical Review." Herpetology Monographs 3 (1989): 142.

Sammouri, R., Sabine Renous, Jean-Marie Exbrayat, and Jean Lescure. "Developpement embryonnaire de Typhlonectes compressicaudus (Amphibia Gymnophiona)." Annimal Science Nature Zoology Paris 11 (1990): 135–163.

Savage, J. M., and M. H. Wake. "A Re-evaluation of the Status of Taxa of Central American Caecilians (Amphibia: Gymnophiona), with Comments on Their Origin and Evolution." Copeia 2001 (2001): 52–64.

Summers, Adam P., and James C. O'Reilly. "A Comparative Study of Locomotion in the Caecilians Dermophis mexicanus and Typhlonectes natans (Amphibia: Gymnophiona)." Zoological Journal of the Linnean Society 121 (1997): 65–76.

Wake, Marvalee H. "Reproduction, Growth and Population Structure of the Central American Caecilian Dermophis mexicanus." Herpetologica 36 (1980): 244–256.

Wake, Marvalee H., and James Hanken. "Development of the Skull of Dermophis mexicanus (Amphibia: Gymnophiona) with Comments on Skull Kinesis and Amphibian Relationships." Journal of Morphology 173 (1982): 203–223.

Wake, Marvalee H., John C. Hafner, Mark S. Hafner, Lorrie L. Klosterman, and James L. Patton. "The Karyotype of Typhlonectes compressicaudus (Amphibia: Gymnophiona), with Comments on Chromosome Evolution in Caecilians." Experientia 36 (1980): 171–172.

Wilkinson, Mark, and Ronald A. Nussbaum. "Evolutionary Relationships of the Lungless Caecilian Atretochoana eiselti (Amphibia: Gymnophiona: Typhlonectidae)." Biological Journal of the Linnean Society 126 (1999): 192–223.

Marvalee H. Wake, PhD