Cryptochiton stelleri Middendorff, 1847 Common name(s): Giant gumboot chiton, Giant Pacific chiton, Chinese slipper
Synonyms:
Phylum Mollusca  Class Polyplacophora   Order Neoloricata    Suborder Acanthochitona     Family Acanthochitonidae
	Cryptochiton stelleri San Simeon, CA
	(Photo by: Dave Cowles, 1995)

How to Distinguish from Similar Species:  No other chiton in this area has all 8 plates covered by the mantle, nor grows this large.

Geographical Range: Aleutian Islands to San Nicolas Island, CA, Kamchatka, Kurile Islands, Japan

Depth Range: Low intertidal to 20 m

Habitat: Rocky substrate, especially in kelp beds.

Biology/Natural History: As with all chitons, this species can grip the rocks tightly.  Its grip is not nearly as strong for its size as is that of many other species, however.  With work one can usually dislodge it.  Unlike some other chiton species, Cryptochiton stelleri has well-developed ctenidia (gills) in the pallial groove beside the foot.  They often raise the edge of their mantle when in air, perhaps to facilitate respiration.  The commensal polychaete worms Arctonoe vittata or A. pulchra can sometimes be found in their pallial groove, as can the pea crab Opisthopus transversus.  O'clair and O'Clair do not report any commensals in this species in SE Alaska, however.  The species spawns from March to May in California., laying eggs in gelatinous, cinnamon-red spiral strings up to 1 m long.  The egg strings do not stick and are quickly broken up by the waves.  When females release their eggs, nearby males are stimulated to release sperm into the water.  After hatching, larvae swim for about 20 h before settling.  Adults do not move far (less then 20 m in 2 years in one experiment) and may live 20 years or more.  Some individuals have algae growing on their mantle.  Feeds mostly on various red algae, and also on some brown and green algae.  Predators include the snail Ocenebra lurida and tidepool sculpins.  Sea otters seem to ignore it, but river otters will eat it..  Indian tribes often ate it.  44% of body weight is blood. The radular teeth are hardened with a magnetite cap.  Named after Georg Wilhelm Steller, an early Russian naturalist in Alaska.

The radular teeth of gumboot chitons contain magnetite (a very hard, magnetic iron-containing compound) and are one of the hardest biomaterials made (Nemoto et al., 2019).  Photos and movies of gumboot chiton radular teeth in action can be seen here and here.

References:

General References:
Morris et al., 1980
Kozloff, 1993
O'Clair and O'Clair, 1998

Scientific Articles:

Nemoto, Michiko, Dongnei Ren, Steven Herrera, Songqin Pan, Takashi Tamura, Kenji Inagaki, and David Kisailus, 2019. Integrated transcriptomic and proteomic analyses of a molecular mechanism of radular teeth biomineralization in Cryptochiton stelleri. Scientific Reports 9: Article 856. doi: 10.1038/s41598-018-37839-2.

Another photo of the underside.  Photo by Dave Cowles, San Simeon, CA April 1997

This species was formerly abundant at San Simeon, CA.  During the latter years of the 1990's I (Dave Cowles) observed large numbers decomposing and washing up onto the beach.  I suspect a disease was affecting them.  Those washing ashore were blotched, as some living individuals are.  I wonder if the blotching seen in living individuals is a sign of disease?  Far fewer can be found there now. I also notice that it is not unusual to see blotched and dying individuals washed up on other beaches.