There are nearly 200 species of caecilians, but most people will never encounter one. That’s because they tend to live underground, burrowing through loose soil and ground litter with their long, streamlined bodies.
Caecilians (pronounced ‘seh-SILL-yuns’) are limbless amphibians that on the surface resemble a worm or a snake. The smaller species measure less than three inches, but the largest one (Caecilia thompsoni from Colombia) grows to almost five feet long.
Read on to discover more about these unusual amphibians.
1) Some have protrusible eyes, others lack them entirely. The word caecilian comes from the Latin “caecus,” which means blind. Some caecilian species are eyeless, while others have small eyes hidden under their skin.
2) Caecilians are the only tentacled amphibians. They have short, sensory tentacles located between their eyes and nostrils that help them probe their environment and find prey.
Gymnopis multiplicata. Photo by Ian VanLare, distributed under a CC BY-NC-ND 2.0 license.3) They come in a rainbow of colors. The skin of caecilians is ringed with folds of skin called annuli, giving them a segmented appearance. Depending on the species, they can be gray, brown, black, purple, green, blue, orange, or yellow. These bright colors may be a warning to predators; some species have poison glands.
4) Caecilian heads are built for burrowing. A hard, thick skull with a pointy snout helps them move effectively through dirt or mud.
5) They move like worms. Caecilians move by hydrostatic locomotion, with their skeleton and deep muscles acting like a piston inside the skin and outer muscles. With their rear ends anchored, they take advantage of forceful muscular compression to drive their heads forward like a hydraulic ram.
6) They’re surprisingly toothy. Caecilian mouths are filled with dozens of needle-like teeth. They tend to eat soil-dwelling invertebrates such as worms and termites, but some species may also grab small snakes, frogs, and lizards. No matter what the meal is, it is swallowed whole.
7) They have super muscular jaws. Most caecilians have two sets of muscles for closing the jaw, as opposed to the single pair most animals possess. These come in handy for burrowing, where they help keep the skull and jaw rigid.
8) Caecilians are the only amphibians to exclusively use internal insemination. Males have a penis-like appendage called a phallodeum, which they insert into the female’s cloaca for mating sessions that can last several hours.
9) They can give birth to live young. About 25% of caecilian species lay eggs, but the other 75% give birth to already-developed offspring. Before birth, baby caecilians use their special scraping teeth to feed on the lining of their mother’s oviduct.
10) Caecilian mothers have a special way of providing for their young. Some baby caecilians have very odd teeth: short, blunt ones built for scraping and long, curved ones, like hooks. It turns out these teeth serve a unique purpose early in life. For several weeks after birth, the young caecilians stay with their mother. During this time, she grows a thick outer layer of skin that is rich in fat and other nutrients. Her babies use their modified teeth to peel her skin off and eat it. This unusual parental care behavior is known as dermatotrophy and seems to be unique to caecilians. Check out this video of young caecilians feeding!
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Schwartz, E. N. F., Schwartz, C. A., and Sebben, A. (1998). Occurrence of hemolytic activity in the skin secretion of the caecilian Siphonops paulensis. Natural Toxins6 (5): 179–182. doi:10.1002/(SICI)1522-7189(199809/10)6:5<179::AID-NT20>3.0.CO;2-M
Wilkinson, M., Sherratt, E., Starace, F., and Gower, D. J. (2013). A New Species of Skin-Feeding Caecilian and the First Report of Reproductive Mode in Microcaecilia (Amphibia: Gymnophiona: Siphonopidae). PLoS ONE 8(3): e57756. doi:10.1371/journal.pone.0057756
