- This clam is often eaten by man, especially by native Americans. When dug up, this clam may not be capable of reburying itself again. 
Common Names in English:
Fat Gaper, Alaskan Gaper, Fat Gaper Clam, Gaper Clam, Horse Clam, Otter Clam, Summer Clam
Species Tresus capax
As with other members
Mactridae, this species has 2 valves
similar to one another and 2 adductor muscle scars
that are similar
in size, has a true hinge plate
with teeth and a socketlike chondrophore
in both valves, a pallial sinus and continuous pallial line
no radial ribs. Tresus capax has a shell
often over 10 cm long (up
to 20 cm) and with a wide gape
(over 1/4 the width of
at the posterior end. The shell is about 1.5 times as long as high,
and the umbones are near the end of the anterior third of the shell.
, where it is still attached, a dark brown or black.
Shell chalky white or yellow. This is the largest intertidal clam
in the northern part of its range
(Alaska), though in Puget Sound
the geoduck clam is larger.
These clams have extremely long siphons which extend up from their deep location to the surface of the mud . The siphons are fised together but the internal channels are separate.
Typically found in the intertidal zone at the water's edge at a mean distance from sea level of 65 meters (212 feet).
Ecology: Commensals include the crabs Pinnixa faba and Pinnixa littoralis, in the mantle cavity . The small male crabs move around but the larger females remain sheltered by a fringe of tissue , the visceral skirt , attached to the clam's visceral mass. They scrape plankton from this fringe.
During the winter this clam depletes its glycogen stores from the gonads . Fat stores (in the digestive diverticula) are only used if the glycogen has been exhausted. In Washington, reaches maturity in 3-4 years. Spawn in winter.
Predators include the moon snail Polinices lewisii, the crab Cancer magister, and the seastars Pycnopodia helianthoides and Pisaster brevispinus. Fusitron oregonensis will attack it if it gets the chance.
- Whittaker & Margulis,1978
- C. Linnaeus, 1758
- (Hatschek, 1888) Cavalier-Smith, 1983
- Grobben, 1908
- (C. Linnaeus, 1758) Cuvier, 1795
- C. Linnaeus, 1758
- Subclass: Metabranchia ()
- Class: Bivalvia () - C. Linnaeus, 1758 - Bivalves
- Phylum: Mollusca () - (C. Linnaeus, 1758) Cuvier, 1795 - Molluscs
- Superphylum: Eutrochozoa ()
- Branch: Protostomia () - Grobben, 1908
- Subkingdom: Bilateria () - (Hatschek, 1888) Cavalier-Smith, 1983
- Kingdom: Animalia () - C. Linnaeus, 1758 - animals
Status: Accepted Name
Last scrutiny: 17-Jan-2006
Tresus nuttallii (uncommon in our region) has a shell more than 1.5x as long as high and the umbones are near the end of the anterior quarter (Ref. 109953)
Members of the genus Tresus
ZipcodeZoo has pages for 5 species and subspecies in this genus:
- Search for Pictures: images.google.com
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- Annual report - Western Society of Malacologists. Pomona, Calif., Western Society of Malacologists. url p. 11, p. 6.
- California fish and game. [San Francisco, etc.]: State of California, Resources Agency, Dept. of Fish and Game. url p. 215, p. 227, p. 227, p. 266, p. 274, p. 286, p. 315, p. 322, p. 324, p. 41, p. 63, p. 64, p. 84, p. 93.
- Check lists of the shells of North America Prepared for the Smithsonian institution, by Isaac Lea, P. P. Carpenter, Wm. Stimpson, W. G. Binney, and Temple Prime Washington, Smithsonian institution1860 url .
- Current bibliography for aquatic sciences and fisheries. London, Taylor & Francis ltd. url p. 135.
- Fishery bulletin / U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service. Washington, D.C.: The Service: url p. 414, p. 430, p. 556, p. 706.
- Journal of ethnobiology. 23 2003 Flagstaff, Ariz.: Center for Western Studies, 1981- url p. 278.
- Memoirs of the San Diego Society of Natural History. 2 1972 San Diego, Calif.: The Society, 1931-1989. url p. 318, p. 376.
- National overview and evolution of NOAA's Estuarine Living Marine Resources (ELMR) Program / David M. Nelson and Mark E. Monaco. Silver Spring. Md.: U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service, National Centers for Coastal Ocean Science, Center for Coastal Monitoring and Assessment, 2000. url p. 42.
- Otia conchologica: descriptions of shells and mollusks from 1839 to 1862 / by Augustus A. Gould, M.D. Boston: Gould and Lincoln, 1862. url p. 252, p. 255.
- Proceedings of the California Academy of Sciences, 4th series. San Francisco, California Academy of Sciences. url p. 350, p. 358.
- Proceedings of the National Shellfisheries Association. Plymouth, Mass., Published for the National Shellfisheries Association by MPG Communications. url , , , p. 1, p. 10, p. 107, p. 11, p. 12, p. 12, p. 126, p. 13, p. 13, p. 3, p. 31, p. 32, p. 35, p. 35, p. 36, p. 37, p. 38, p. 39, p. 41, p. 42, p. 43, p. 44, p. 45, p. 46, p. 5, p. 51, p. 57, p. 6, p. 68, p. 7, p. 7, p. 8, p. 88, p. 9, p. 90.
- Smithsonian miscellaneous collections. 2 1862 Washington: Smithsonian Institution, 1862-1968. url p. 1, p. 110.
- The Biological bulletin. Woods Hole, Mass.: Marine Biological Laboratory, url p. 115, p. 124, p. 128, p. 224.
- The Canadian field-naturalist. Ottawa, Ottawa Field-Naturalists' Club. url p. 123.
- The mollusks of western North America. Washington, Smithsonian Institution, 1872. url .
- Washington State Coastal Zone Management Program amendment no. 3: approval of the Grays Harbor estuary management plan: program draft environmental impact statement. [Olympia, Wash.?]: Grays Harbor Regional Planning Commission; 1983. url p. 13.
- Brands, S.J. (comp.) 1989-present. The Taxonomicon. Universal Taxonomic Services, Zwaag, The Netherlands. Accessed January 16, 2012.
Accessed through GBIF Data Portal November 18, 2007:
- Institute of Marine and Coastal Sciences, Rutgers University, Gwaii Haanas Invertebrates
- Marine Science Institute, UCSB, Paleobiology Database
- University of Alaska Museum of the North, University of Alaska Museum of the North Mollusc Collection
- Biodiversity Heritage Library NamebankID: 2693278
- Catalogue of Life Accepted Name Code: ITS-80955
- Global Biodiversity Information Facility Taxonkey: 13782335
- Integrated Taxonomic Information System (ITIS) Taxonomic Serial Number (TSN): 80955
- Zipcode Zoo Species Identifier: 512454
- Cowles, Dave. Key to Invertebrates Found At or Near The Rosario Beach Marine Laboratory (a campus of Walla Walla University) Fidalgo Island, Anacortes, WA May 2009. [back]
- Standard Deviation = 132.870 based on 34 observations. Terrestrial altitude and ocean depth information for each observation from British Oceanographic Data Centre. [back]