Gumboot chiton

Gumboot chiton
Conservation status
Least Concern
Scientific classification
Kingdom: Animalia Phylum: Mollusca Class: Polyplacophora Order: Neoloricata Suborder: Acanthochitonina Family: Acanthochitonidae Genus: Cryptochiton Species: C. stelleri
Binomial name
Cryptochiton stelleri (Middendorff, 1847)

The gumboot chiton, Cryptochiton stelleri, also known as the giant pacific chiton, is the largest of the chitons, growing to 33 cm (13 in). It is found along the shores of the northern Pacific Ocean from Southern California to Alaska, across the Aleutian Islands to the Kamchatka Peninsula and south to Japan.^[1] It inhabits the lower intertidal and subtidal zones of rocky coastlines.

Chitons are molluscs somewhat resembling snails, but rather than a single shell, they have eight armored plates (called valves) running in a flexible line down their back. Unlike most chitons, the gumboot's valves are completely hidden by its leathery upper skin or girdle, which is usually reddish-brown or brown in color, or occasionally orange.

Names

The name "gumboot" seems to derive 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^[2] says it is named "from the animal's resemblance to the rubber, or gum, boots worn by Alaska's coastal residents."

The Latin name Cryptochiton stelleri means Steller's hidden chiton. "Steller" is in honor of the 18th-century German zoologist Georg Wilhelm Steller, who first described many species of the northern Pacific seashore. "Hidden" could refer to the camouflaged appearance of the creature, which is hard to spot among the rocks it so resembles.^[3] Many taxonomic names for chitons are based on the appearance of their plates or valves, however, so it is more likely that the "hidden" portion of the name originally referred to the valves being completely obscured by the gumboot's girdle.^[4]

Life

The underside of Crytochiton stelleri, showing the foot, in the center, surrounded by the gills and mantle. The mouth is visible above and to the left of the foot.

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.^[5] 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.^[6]

The gumboot can live for 20 years. It has few natural predators, the most common being the lurid rocksnail, Ocenebra lurida — although the small snail's efforts to consume the chiton are generally limited to the outer mantle only. It is sometimes reported that the lurid rocksnail is in fact the gumboot chiton's only predator^[7], but others list such animals as the sea star Pisaster ochraceous^[8], some octopus species^[9], and the Sea Otter^[10].

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. One researcher^[11] found that more than a quarter of gumboots hosted an Arctonoe vittata, a pale yellow scale worm which can grow to 10 cm long. Opisthopus transversus, a small crab, is also sometimes found within the gills.^[12]

Human interaction

Its flesh is edible, and has been used as a food source by Native Americans, as well as by Russian settlers in Southeast Alaska.^[13] However, it is not generally considered palatable, with a texture described as extremely tough and rubbery. The writers of Between Pacific Tides further detail 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."^[14]

The gumboot chiton's bony armoring plates, called "butterfly shells" due to their shape, can sometimes be found washed up on beaches, as can whole chitons: the gumboot keeps a weaker grip on the rocks that make up its home than most chitons and it is not unusual for them to be knocked loose in heavy waves.

References

• Ricketts, Edward; Calvin, Jack; Hedgepeth, Joel (1992). Between Pacific Tides (5th edition). Stanford University Press. ISBN 0-8047-2068-1. 
• Sheldon, Ian (1988). Seashore of the Pacific Northwest. Lone Pine Publishing. ISBN 1-55105-161-3.  p. 92
• Gumboot chiton, From the Monterey Bay Aquarium Online Field Guide.
• Taxonomic data from ITIS, the Integrated Taxonomic Information System.
• Cowles, Dave (2005). Cryptochiton stelleri; includes photos of underside.

Notes

1. ^ Ricketts et al p 105. Also Cowles.
2. ^ Fields, Carmen (1999). Alaska's Seashore Creatures: A Guide to Selected Marine Invertebrates. Alaska Northwest Books. ISBN 0-88240-516-0.  p. 27.
3. ^ BioMEDIA's Gumboot Chiton page
4. ^ This explanation is offered by Patricia Lichen's Brittle Stars & Mudbugs p. 102 (Sasquatch Books, 2001).
5. ^ Cowles.
6. ^ Ricketts et al p 103.
7. ^ The Monterey Bay Aquarium reports this.
8. ^ http://www.racerocks.com/racerock/eco/taxalab/ensy02/sarahm.htm
9. ^ ibid.
10. ^ Perrin, William et al (2002). Encyclopedia of Marine Mammals. Academic Press. ISBN 0-12-551340-2.  p 847.
11. ^ Ricketts et al p 105
12. ^ ibid.
13. ^ Ricketts et al p 103.
14. ^ ibid.

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