Siliqua patula (Dixon, 1788)

Common name(s): Razor clam, Pacific razor clam, Northern razor clam, Giant pod

Synonyms:
Phylum Mollusca
 Class Bivalvia
  Subclass Heterodonta
   Order Veneroida
    Family Cultellidae
Siliqua patula, about 11 cm long, at Kalaloch, WA.  The hinge is on the lower side in this photo and the foot is starting to be extended for digging
(Photo by: Dave Cowles, July 2005)
Description:  As with all members of family Cultellidae, this large clam species is more than twice as long as it is wide, has a true hinge plate, 2 adductor muscle scars of similar size, and a shiny brown or olive periostracum.  They are not more than 3x as long as high, and the dorsal margin is not concave.  Siliqua patula is a large clam (grows much larger than 5 cm), olive-green or olive-brown with perhaps some purple near the umbones, and the internal supporting rib diverges from the dorsoventral axis by about 30 degrees (photo).  Shell, up to 17 cm long and rounded at the ends, is thin and cracks easily.  In a live animal the valves gape everywhere but at the hinge, and the siphons are fused (photo).  The shell interior is white with pinkish tint (photo).

How to Distinguish from Similar Species:  The other related species in this area are less than 5 cm, subtidal, and with alternating colored bands on the shell.  The jackknife clams (genus Tagelus and Solen) are also smaller and much more elongated.

Geographical Range:  Bering Sea, Alaska to Pismo Beach, CA (Rarely seen in central CA)

Depth Range:  Intertidal to 55 m

Habitat:  Low intertidal and subtidal on flat, sandy exposed beaches.  Burrows deeply and rapidly into the sand.

Biology/Natural History:  Spawns late spring and summer.  In Washington spawning is simultaneous (the same day) along several kilometers of beach, triggered by a sudden rise in water temperature to about 13C (usually in late May or June).  Intensity of spawning varies dramatically from year to year.  In Alaska they spawn every year, but not simultaneously, in July and August.  Larvae are pelagic for about 8 weeks.  Live about 12 years in Washington.  This species is frequently dug by humans for food, but as with most species on the open coast, is susceptible to paralytic shellfish poisoning (PSP, toxic to humans) due to ingesting too many dinoflagellates such as Gonyaulax during the summer.  The animal typically remains just below the surface, with a dimple in the sand above the siphon.  When disturbed, for example by human footsteps approaching, it begins digging rapidly.  Predators include flatfish such as the starry flounder and the Dungeness crab Cancer magister.  May have a commensal nemertean worm, Malacobdella grossa, or the pea crab Pinnixia faba in its mantle cavity.

These clams are called razor clams for a reason.  If while a clam digger grasps the ventral side of the shell in the rush to catch up with the rapidly-digging clam, he may pay for it with a deeply cut hand.  Fortunately, the clams always orient with the hinge toward the ocean so if a digger will always reach into the hole on the oceanward side he will be safe from cuts (but will still have to dig fast!)



 
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References:

Dichotomous Keys:
  Flora and Fairbanks, 1966
  Kozloff 1987, 1996
  Smith and Carlton, 1975
 

General References:
  Brusca and Brusca, 1978
  Carefoot, 1977
  Harbo, 1997
  Harbo, 1999
  Johnson and Snook, 1955
  Kozloff, 1993
  McConnaughey and McConnaughey, 1985
  Morris, 1966
  Morris et al., 1980
  Niesen, 1994
  Niesen, 1997
  Ricketts et al., 1985
  Sept, 1999

Scientific Articles:
 

Web sites:
 



General Notes and Observations:  Locations, abundances, unusual behaviors:



This species is a rapid digger, as shown by this series of photos taken within a short time of one another.  In the photo above, the posterior end with the siphons is to the left.
The foot has been extended out of the anterior end of the shell on the right, pressed into the sand, expanded, and is being retracted to pull the shell downward.
In the photo below the clam has pulled itself farther into the sand and is proceeding to bury itself out of sight.
Photos on low intertidal beach at Kalaloch, WA by Dave Cowles July, 2005



The shell is white with a pinkish tinge inside.  It has a supporting rib running from the hinge toward the ventral side at about a 30 degree angle.
The shell is thin and fragile.
Photo by Dave Cowles, October 2005

The photos below are of a small individual (8.5 cm long) found on the beach at Monterey Bay.  The left valve is broken.  Photos by Dave Cowles, August 2010
Outside
Inside



Authors and Editors of Page:
Dave Cowles (2005):  Created original page