Snaggle-tongue of the Gumboot Chiton

Cryptochiton stelleri

Yuck! What devilry is this? It's like that bit in Jurassic Park with the giant T. rex eye except he's made of mash potato and appears to be staring actual daggers.

What it really is, is the despicable tongue of the Gumboot Chiton.

Image: Ed Bierman

Chitons are molluscs that crawl over the ocean floor on a sticky foot. It sounds familiar, but these are no slugs or snails. They aren't even gastropods. They belong to their very own class known as Polyplacophora, or Bearer of Many Plates. The plates in question being the eight, overlapping valves that make up their shell.

There are thousands of Chiton species found all over the world, usually in shallow, intertidal waters, and most of them are only 5 cm (2 in) long or less. Gumboots are on the other side of the scale. They reach over 30 cm (a foot) long! They're found in the north Pacific, from Japan to Russia, Alaska and California.

In most Chitons the plates are clearly visible as thick bands of armour covering their backs. Not so in the Gumboot, their plates are entirely covered in leathery skin. They end up looking like a lumpy puddle enjoying a crawl in low tide.

Video: vichigh marine

Check out the underside and you'll see that they also enjoy the use of a diabolically disturbing mouth. Like other molluscs, Chitons have what's known as a radula. It looks a bit like a tongue in that it's quite long and, like real tongues, it's situated behind the mouth and in front of the oesophagus. Unlike real tongues, it's made of tough chitin and it's covered in teeth.

Chiton radulas are particularly special because the teeth are reinforced with an incredibly tough, magnetic mineral called magnetite. They're so magnetic that if you put a Chiton's radula in water, it will turn to face north. Just like a dog using the bathroom, but less messy.

Image: kathleenreed

With this apparatus Chitons are able scrape algae off of rocks. It's not the kind of thing I'd do with either my tongue or my teeth, buts Chitons always have a supply of fresh, new teeth to step into the breach when old ones wear away.

It's not bad for something that looks a lot like one, gigantic tongue.