The rubber eel (Typhlonectes natans) is a nocturnal, fully aquatic caecilian that occurs in South America, specifically in the northwest region of the continent (Duellman and Trueb, 1986; Pough et al., 2004). Caecilians are a group of limbless amphibians. Limbs and limb girdles are absent in all extant caecilians and the majority of species also lack a tail. Extant caecilians comprise 33 genera and 170 species that may be aquatic, terrestrial, or fossorial. They are distributed throughout the tropics, although they are not found in Madagascar, central Africa, or the Oceanic region. Caecilians are the least studied group of amphibians because most species spend the majority of their lives underground or underwater (Pough et al., 2004).

Caecilians differ from other amphibians in having a compact skull, a trait known as stegokrotaphy. The skull is completely roofed except for openings for the eyes, nares, and tentacle. However, some species have an open temporal region to facilitate kinetic movement of the skull, a trait known as zygokrotaphy. All caecilians have a fused maxilla and palatine, known as the maxillopalatine. Additionally, all the occipital elements and the paraspheniod are fused into a single element called the Os basale. In derived species of caecilians such as Dermophis mexicanus and Typhlonectes natans, the nasals and premaxillae also fuse to form the nasopremaxilla (Duellman and Trueb, 1986; Pough et al., 2004). All caecilians have a unique chemosensory organ located on the head called the tentacle. The tentacle exits the skull through the tentacular foramen or groove located between the nares and orbit (Pough et al., 2004).

Reproduction in caecilians is oviparous or viviparous and fertilization is internal. Although some oviparous species lay eggs in water, other species deposit eggs terrestrially and maternal care for the eggs is common. Most oviparous species have aquatic larvae but direct development occurs in some terrestrial species. In viviparous species, embryos are nourished by secretions from oviduct walls of the female. Specialized fetal teeth in the young are used to stimulate cells in the oviduct walls to produce secretions (Pough et al., 2004). Typhlonectes natans is a viviparous species. Females have a gestation period between six and seven months and a litter averaging between two and eleven young.

Additional Information on the Skull

Click on the thumbnails below for labeled images of the skull in standard anatomical views.

Dorsal view	Lateral view	Ventral view

This specimen was collected from Depto. Atlantico, Colombia, at Cano Soledad, Cienega Santo Tomas, Rio Magdalena, near Barranquilla (Lat: 10.766667, Long: -74.750000) by M.H. Wake and G. Neilsenon January 1 1978. It was made available to The University of Texas High-Resolution X-ray CT Facility for scanning by Dr. David Cannatella of The University of Texas and the Amphibian Tree of Life project (EF-0334952). Funding for scanning and image processing was provided by Dr. Cannatella's grant, and funding for additional image processing was provided by a National Science Foundation Digital Libraries Initiative grant to Dr. Timothy Rowe of The University of Texas at Austin..

Specimen Photos

Dorsal view	Lateral view	Ventral view

This specimen was scanned by Matthew Colbert on 21 September 2004 along the coronal axis for a total of 660 1024x1024 pixel slices. Each slice is 0.0294 mm thick, with an interslice spacing of 0.0294 mm and a field of reconstruction of 12 mm.

Literature

Duellman, W. E. and L. Trueb. 1986. Biology of Amphibians. Johns Hopkins, Baltimore, 670 pp.

Pough, H. F., R. M. Andrews, J. E. Calde, M. L. Crump, A. H. Savitzky, and K. D. Wells. 2004. Herpetology. Pearson Education, Inc., Upper Saddle River, NJ, 726 pp.

Nussbaum, R. A., and M. Wilkinson. 1989. On the classification and phylogeny of caecilians (Amphibia: Gymnophiona), a critical review. Herpetological Monographs 3:1-42.

Wake, M. H., J.-M. Exbrayat, and M. Delsol. 1985. The development of the chondrocranium of Typhlonectes compressicaudus (Gymnophiona) with comparison to other species. Journal of Herpetology 19:68-77.

Wilkinson, M., and R. A. Nussbaum. 1999. Evolutionary relationships of the lungless caecilian Atretochoana eiselti (Amphibia: Gymnophiona: Typhlonectidae). Zoological Journal of the Linnean Society 126:191-223.

Links

Typhlonectes natans on the Amphibian Species of the World website (American Museum of Natural History).

Information and images of T. natans on AmphibiaWeb (Univ. of California, Berkeley)

Front page image.