It was soft, rubbery and lubricious, a humongous earthworm to the untrained eye. I was pretty happy with my find until the joy of the moment was momentarily ruined when the ‘worm’ turned.
It opened its mouth and sank its teeth into me. “Ow! It bites!” I didn’t expect a mouth, let alone one lined with teeth. But it seems there’s nothing typical about caecilians. That creature making a squirming getaway into the swampy vegetation by my feet is one of the oddest and most overlooked of all amphibians.
Say ‘amphibian’ and most folk think of frogs, toads and salamanders, the mostly leggy, lively, surface-living orders of their class.
The secret caecilians, in contrast, are often forgotten, remaining hidden beneath the litter and soil and in the swampy waters of the world’s warmer and wetter places. A habit that means the 220-odd (in more ways than one) species are rarely seen by anyone but the most determined.
What is a caecilian?
There is a lot about caecilians that is weird. In addition to having a thin, permeable skin, they appear to have very little in common with other amphibians or indeed other animals. Their simple bodies have no clear demarcations that suggest a head, torso or abdomen. They lack limbs, a few are missing tails and, if they’ve got eyes at all, they’re not very well developed – the name caecilian translates from Latin as ‘blind one’.
The fact that they have jaws with several rows of formidable jagged teeth is not even the half of it. They have recently been identified as the only amphibian to possess venom glands, too. These supply grooves in their teeth – perfect for grabbing and overpowering slippery or challenging prey.
The simple, worm-like body is a tried-and-tested design in nature. Smooth, streamlined and well-muscled, they have no appendages to get in the way, making them highly efficient for a skulking and burrowing lifestyle.
Most amphibians have delicate skulls composed of a collection of loosely articulated, thin bones. Caecilians are the opposite: theirs are solid, with thick bones fused to form the perfect device to push their way through their environment as well as anchor the powerful jaw muscles.
How do caecilians mate?
Some give birth to live young, which develop inside their mothers, each with huge gills that act like placentas while they are growing, only to be shed on birth. The males even have a ‘pseudo penis’-like organ for inseminating the females, and they all have a pair of unique sensory organs called tentacles.
Do caecilians have eyes?
The lack of complex eyes – most have at best a small, simple eye, deeply embedded in the skin – means there is nothing delicate to damage. And besides, where they reside in the realm of dinginess and dank, they don’t really need them.
Instead, their body surface is equipped with multiple sensory organs, which include a fish-like lateral line in some species. Strangest of all, though, is a pair of tentacled organs between their eyes and nostrils, which are thought to be used for tasting and sensing the environments around them.
A family of African caecilians, the Scolecomorphids, have their eyes and tentacles so closely positioned that when the tentacle is extended, their eyes move out of their socket in the skull and down the tentacle itself. A small pigment-less area of skin in the tentacles allows the light to reach the retina.
How do caecilians raise their young?
But it’s with their maternal care plan that things get seriously weird, in particular with some of the egg-laying species. Maternal care is already an unusual quality in an amphibian – not many look after their young. But some caecilian mothers feed their young a nutritional ‘milk’ produced by glands on the surface of her skin.
It gets weirder still in some members of the Herpelid and Siphonpidae families. These go in for a behaviour called ‘maternal dermatophagy’. This is where the shark-mouthed babies take mouthfuls out of their mothers flanks. While her offspring are growing, she helps them out by developing a special outer layer of skin rich in nutrients. This is constantly replaced, allowing the newly hatched juveniles to gain more than 10 times their original weight in a week. Now that’s some parenting.
Top image: a Cayenne caecilian. Credit: Getty
