Invertebrates
Gumboot Chiton
Cryptochiton stelleri · also called wandering meatloaf, giant Pacific chiton
The gumboot chiton looks like a slab of meatloaf someone left on a rock, and it moves about as fast. It is the biggest chiton in the world, its armoured shell is hidden under leathery skin, and it grazes seaweed with a tongue that can scrape solid rock.
Overview
Cryptochiton stelleri lives on wave-swept rock in the cold northern Pacific, from California to Alaska, Kamchatka, and Japan. At 33 to 36 cm and over a kilogram it is far larger than any other chiton, and it can live 40 years or more. It grazes red and green seaweed at night.
The hidden shell
Most chitons show eight overlapping shell plates down the back. In the gumboot chiton, a thick leathery red-brown skin grows completely over the plates, so the shell is internal and the animal looks like a smooth lump — hence “wandering meatloaf.”
Rock-scraping teeth
The tips of its radula teeth are capped with magnetite, making them among the hardest materials any animal produces, stiff enough to rasp stone. Researchers study them as a model for durable coatings.
Status
Least Concern and common on cold Pacific rocky shores, though slow-growing and long-lived, so disturbed populations recover only over many years.
Gumboot Chiton: common questions
Why is it called the wandering meatloaf?
The nickname describes what the animal looks like. A gumboot chiton is a large, oval, dull reddish-brown lump with a soft, slightly pebbled, leathery surface and no obvious features, and it inches along the rocks at a crawl, so people have long compared it to a slab of meatloaf that has decided to go for a walk. The name was around among tidepoolers and naturalists for years and then spread far more widely in 2021, when a research paper on the unusual iron mineral in its teeth was widely reported and headline writers seized on the meatloaf image.
Where are the chiton's shell plates?
They are still there, but you cannot see them from the outside. Like all chitons, the gumboot chiton has a shell made of eight separate curved plates running down its back, which in most chitons are exposed and give the group its armoured, segmented look. In this species the fleshy girdle around the edge of the body has expanded and grown up and over the plates, covering them completely with tough skin, so the shell is entirely internal. If you find a dead gumboot chiton that has decayed, the eight butterfly-shaped white plates are often left behind, and beachcombers collect them.
How can an animal have teeth hard enough to scrape rock?
The gumboot chiton, like other chitons, grows a continuous belt of teeth on its radula, the ribbon-like feeding organ it drags over rock surfaces to rasp off algae. As the front teeth wear down and break off, new ones move up from behind. The working teeth are reinforced at the tip with magnetite, a hard, stiff iron oxide that the animal builds up biologically from iron it collects, producing one of the hardest and most wear-resistant biominerals known. Materials scientists have mapped how the chiton assembles this coating, hoping to copy it for durable industrial surfaces.
Is the gumboot chiton dangerous or is it safe to pick up?
It is completely harmless. It has no venom, no bite that can reach a person, and no sharp parts; the radula only works against rock and seaweed at very close range. It is safe to touch gently in a tidepool. The main concern is for the animal, not the handler, since a gumboot chiton clamped to rock is holding on hard against waves, and prying one off can tear the foot and leave it unable to reattach before a predator or the surf gets it, so the usual tidepool rule applies of looking without lifting.