Gumboot Biology!

Ever stumble across something so primitive looking that you think it must just be a rock? I think the chitons fall into that category, particularly the gumboot chiton. A chiton is a Greek tunic, a type of dress like clothing ... personally I wouldn't want to wear this thing. The name actually comes from a combination of Greek and Latin. The Latin term chitōn, means "mollusc", and is derived from the Greek word "khitōn", meaning tunic. The Greek word "khitōn" can be traced to the Central Semitic word "*kittan", which is from the Akkadian words "kitû" or "kita’um", meaning flax or linen, and originally the Sumerian word "gada" or "gida". Bet that's more than you ever wanted to know about a weird animal's name....but it does highlight how cool the language of our environment really is.

Anyway!

Chitons (in general) are smallish, primitive marine molluscs in the class Polyplacophora. There are 900 to 1,000 extant species of chitons in the class, which was formerly known as Amphineura). They are sometimes called sea cradles or "coat-of-mail shells" and it's easy to see why they garnered the latter name. They have a shell which is composed of eight separate shell plates that overlap somewhat at the front and back edges, and yet the plates articulate well with one another. Although the plates provide good protection for impacts from above, they permit the chiton to flex upward when needed for locomotion over uneven surfaces and allows them to slowly curl up into a ball when dislodged.

The gumboot chiton, Cryptochiton stelleri, is the monster of the chitons, growing to 33 cm (13 in). You can find these things (if you look hard enough) along our shores in the northern Pacific Ocean. They hang out in the lower intertidal and subtidal zones of rocky coastlines and their range extends from Southern California to Alaska, across the Aleutian Islands to the Kamchatka Peninsula and south to Japan. Unlike most chitons, the gumboot's armored plates are completely hidden by its leathery upper skin, which is usually reddish-brown or brown in color, or occasionally orange.

Alive, they are challenging to find, their size, shape and colour basically makes them look like any other rock. But what an interesting rock! Their bony armor are often called "butterfly shells" due to their shape (see below). If you are poking around in the rocks on the beach and come across something that is made of shell, but doesn't resemble any clam you've ever seen...it could very well be a chiton plate. Sometimes you might find the whole chiton washed up on shore, the gumboot apparently doesn't have the strongest grip of the chitons (the bigger they are the harder they fall?) and in heavy storms they sometimes lose their grip on the rocks.

The name "gumboot" is assumed to come from a resemblance to the sole of a rubber Wellington boot or gumboot, although support for this apparent etymology is scanty; the Giant Pacific Gumboot Chiton Homepage states "it has reminded others of the sole of a gum rubber boot", and an Alaskan seashore field guide says it is named "from the animal's resemblance to the rubber, or gum, boots worn by Alaska's coastal residents." Check out the underside and make your own decision.

The gumboot chiton's underside is orange or yellow and consists mostly of a large foot similar to that of other molluscs like snails or slugs, with gills found in grooves running along the outer edge of the foot. The gumboot chiton is found clinging to rocks, moving slowly in search of its diet of algae, scraped off of rocks with its rasp-like retractable radula, covered with rows of magnetite-tipped teeth. It also eats other marine vegetation such as sea lettuce and giant kelp. A nocturnal creature, the gumboot generally feeds at night and often remains in a hiding place during the day — although on foggy days it may be found exposed in tide pools or on rocks.

Life Span and Predators

The gumboot can live for 20 years (probably longer than your rubber boots will last!) and there aren't a lot of other things out there that actively hunt them...not that it would be that difficult to stalk one...once you actually saw it..... There are a few snails that like to nibble on them although their efforts to consume the chiton are generally limited to the outer mantle only. The purple sea star Pisaster ochraceous, some octopus species, and the Sea Otter may also snack on them.

House and Home

They aren't just another pretty face though...they also provide shelter for other wayward critters, although I doubt you'll find them in the pages of House and Home any time soon. Several other animal species have been observed living within the gumboot's gills; the relationship is thought to be commensal: neither harmful nor helpful to the chiton. Apparently about 25% of gumboots harbour a pale yellow scale worm which can grow to 10 cm long. Opisthopus transversus, a small crab, is also sometimes found within the gills.

Dinner Anyone?

Apparently...you can eat them...if you want....They have been used as a food source by Native Americans, as well as by Russian settlers in Southeast Alaska. However, with a texture described as extremely tough and rubbery they aren't exactly palatable (at least so I'm told). A former Invertebrate Zoology Professor of mine at UBC, known for attempting to eat pretty much every organism he studied ("You've got to eat your organism" he once said to me...thus I study salmon! No problem there!). One of the authors of Between Pacific Tides, he details the culinary drawbacks of the gumboot: "After one experiment the writers decided to reserve the animals for times of famine; one tough, paper-thin steak was all that could be obtained from a large cryptochiton, and it radiated such a penetrating fishy odor that it was discarded before it reached the frying pan." YUM! Pass the ketchup please?

Want more? (And who wouldn't!)

Ocean Link Gumboot Chiton page

Monterey Bay Aquarium Online Field Guide

Puget Sound Snail and Chiton Photos

Pacific Gumboot Chiton Homepage

Last growth spurt on September 18, 2008