Caecilian

Image: teague_o via Flickr

It's that time again, everyone! When we sit back and relax, kick off our shoes and put our feet up, only to realise we could be doing so much more.

Arms and legs... aren't they mostly just stressful? Are they not impediments to true peace of mind? Don't all relaxation techniques centre on forgetting those tyrant limbs and realising your inner snake?

That's what Caecilians seem to think!

And I'm not talking about Sicilians. Those Mafia guys remove limbs for completely different reasons and they tend not to be relaxing at all.

Caecilians are some 200 amphibians of the order Gymnophiona, found throughout tropical regions like South America, Africa and Southeast Asia.

Image: Henk Wallays

These are the most mysterious and understudied of all the amphibians. You might remember that a whole new family was discovered just recently, hidden underground all this time.

Caecilians are fossorial, or burrowers. This virtually guarantees weirdness. And they don't disappoint.

We'll start with the obvious. It's a tetrapod, but it has no... pods!

Caecilians are yet another example of how legs just get in the way when you're digging through the earth. Earthworms, perhaps the world's foremost rock star burrowers, are the diggers that all others seek to emulate. Caecilians go a step further than most by having folds on their skin to look even more like a segmented worm. Best form of flattery, right?

They can also be long and slender like a worm or much more thick and stout. Either way, most Caecilians don't actually have a tail. Its all body! And if a tail is present it will be extremely short.

Shiripuno

The smallest Caecilians are some 7 cm (2.4 in) long. Even that's comparable to an average earthworm! The biggest ones, though, can reach 1.5 metres (5 ft)! Pretty darn big! But we know that some earthworms can stretch to twice that. Being able to find out weird things like that is probably the main thing that makes the torment of arms and legs worthwhile.

Image: Sean Michael Rovito

The other thing one might confuse Caecilians for are snakes. People who hate snakes might even find that Caecilians are even more snaky than actual snakes. Why? Because snakes aren't wet and slimy but Caecilians are.

Like most amphibians, Caecilians need to keep moist so that they can breathe through their skin.

A couple Caecilians don't even have lungs, and one of those is over 80 cm (2.6 ft) long and the biggest lungless tetrapod in the world! That particular species also has its nostrils sealed up and internal, just to make sure. Seriously, when a Caecilian is done with a body part, they are utterly ruthless!

Anyway, most Caecilians breathe via their skin, mouth and lungs. It's quite an array. Clearly lack of limbs doesn't imply lack of choice.

Image: Henk Wallays

So what's life like for a Caecilian?

Well, while there are a few who are aquatic, most of them only ever burrow through the earth and are seldom seen above ground.

They have extremely tough, bony skulls to help them bulldoze soil out of the way. These brain boxes are incredibly solid, with various parts fused together and scarcely any spaces or gaps anywhere.

And then their skin is fused directly onto the bone! It prevents any terrible "rip and tear" accidents as they push through the soil. Also they're not in a constant state of Chinese burn everywhere they go.

Aside from nostrils to fill those lungs, another gap in the skull is for the eyes. Caecilians don't really use them though. Eyes are kept under the skin, under bone or are absent entirely. When they're there at all, they can only really discern light from dark. For an underground animal, that's basically home from not-home.

Image: Wikimedia
The white patch between eye and nostril
is the retracted tentacle

Far more important, and unique among tetrapods, are their tentacles. They have two small, retractable tentacles between the nostrils and eyes. They enhance the sense of smell so they can find stuff to eat like termites, slugs, earthworms (cannibal!) and beetle pupae. They're so important that they occupy their own holes in the skull. They even use muscles and other structures that would otherwise be part of the eyes. These guys don't see in the dark at all. No need for carrots.

Speaking of muscles, this seems to be a problem presented by their incredibly solid skull. They could've ended up as slack jawed yokels, simply lacking the space for mouth-closing muscles! OK, it's not that bad, but the jaw muscles we all use are reduced and weakened in Caecilians. They're answer is to repurpose a whole other muscle, ensuring a strong bite. Caecilians are unique in having two sets of muscles for closing the jaw.

Armed with this MacGyver solution (deh-deh deeeeeh) large Caecilians can catch and eat lizards and frogs, killing them in the process. Something MacGyver would never do. He would've found a way to eat them without killing them, before escaping on the wave of an explosion that doesn't kill anyone.

Image: Museum of Comparative Zoology, Harvard University
Backward reclining teeth

Adult Caecilians have backward reclining teeth that can be sharp and dual-cusped, perfect for keeping a strong grip. Coupled with the same kind of toxic skin glands that many salamanders and frogs have, and you can see that Caecilians are a little more painful than any earthworm.

Thing is, baby Caecilians have teeth too, but really weird ones. In fact, Caecilians are altogether extremely peculiar when it comes to breeding.

Here's another bit of uniqueness from the Caecilian. Other amphibians have a cloaca, an all-purpose, posterior evacuation point for absolutely everything (EVERYTHING). This is the same for most birds. What I mean to say is... no penis. :(
But Caecilians are unique among amphibians in that they can evert their cloaca to form a makeshift penis. Better than nothing, I suppose. Maybe that's what they traded their limbs for? Totally worth it!

Alright, yeh. Females are involved, too. They don't appear to make any effort to grow a penis. They have other things to worry about.

Image source
Larval Caecilian with gills.

Most Caecilians lay eggs which the mother will guard. Sometimes what emerges is a larval Caecilian. It has gills and lives in water, just like salamanders. Others will skip that and metamorphose within the egg so that a small version of the adult hatches out.

Some Caecilians do something a little more horrible.

The egg hatches and what comes out looks quite a lot like the adult, but it can't actually look after itself. Its bones and muscles are just too weak.

For other creatures, this is where beautiful things happen. Adorable young mammals suckle from mother and a loving bond is established. Or grim looking bird chicks shriek until mother lovingly regurgitates partially digested caterpillars into their gaping cakeholes.

Baby Caecilians are different. They eat their mother's skin.

globalzoo

This is unique! It's actually not uncommon for amphibians to eat their own shed skin, to say nothing of insects and such. It's a little difficult to imagine for we who shun our own spittle if we see it, and yet are in a constant state of drinking saliva when we don't see it. That's the kind of thing we don't normally think about. But feeding your skin or saliva to someone else? That's different. That, dear reader, is love.

Baby tooth!

And because mother loves her little ones, her specially grown maternal skin is rich in fat and nutrients and regrows every few days. And because youngsters are ungrateful little... anyway, they have strange, complex teeth, perhaps blunt, perhaps hooked, but all for scraping and tearing off reams of skin to chow down.

But then you have the ones that give birth to live, well developed young. Uh oh. There's no placenta here. Caecilians don't have a belly button. The living unborn are instead armed with special teeth. And they use them to feed on a special lining of their mother's oviduct. It's all very... special.

On the one hand it's also utterly disgusting. On the other... isn't it amazing the lengths a mother will go to find a way to provide for her young? I should point out that mother Caecilian survives to do it all over again later. But... I guess getting your skin eaten isn't quite the ultimate sacrifice. Kinda high up, though isn't it?