Leukoma staminea (Conrad, 1857)

Common name(s): Littleneck clam, Common Pacific littleneck, rock cockle, hardshell clam, Tomales Bay cockle, rock clam, ribbed carpet shell

Synonyms:  Paphia staminea, Venerupis staminea, Protothaca staminea, Protothaca restorationensis
Phylum Mollusca
 Class Bivalvia
  Subclass Heterodonta
   Order Veneroida
    Family Veneridae
Leukoma staminea.
(Photo by: Dave Cowles, July 2007)
Description:  As with other clams of family Veneridae (a very large family called the Venus clams), this species has a porcelain-type (chalky) shell, the umbo is anterior to the midline (and to the hinge) but still closer to the center of the shell than to the anterior end, the hinge has 3 cardinal teeth in each valve (photo), and a definite pallial sinus is present (photo).  Other characteristics of family Veneridae include: 2 valves more or less oval or heart shaped, similar in size, and at least 1/4 as wide as long, valves are not subdivided into sections by major grooves or differences in texture, do not have winglike extensions near the umbo, have two adductor muscle scars of similar size (photo), have no chondrophore, pallial line is continuous (photo), hinge ligament is mostly or completely external (photo).  This species has many radial ribs which may be more or less prominent than the concentric ridges.  The concentric ridges are most prominent in the anterior half.  The hinge ligament is about 1/3 the length of the shell (photo).  The siphons are fused all the way to the end and have black tips (photo).  The valves are whitish inside without a purple stain (photo) and have a row of very small teeth along the inside of the ventral margin (photo).  The pallial sinus is deep and pointed (photo).  The shell is whitish, gray, yellowish, or brown with little periostracum on the outside and may have zigzag brown markings or brown splotches.  It usually does not exceed 6 cm long, max 7 cm..

How to Distinguish from Similar Species:  Look especially for the fine teeth on the inside ventral margin of the shell.   Venerupis philippinarum, the Manila clam or Japanese Littleneck, is longer than it is high and its radial ribs are usually more prominent than in this species.  Its siphons are not fused all the way to the tips, and the ventral margin of the shell has no fine teeth.  Saxidomus gigantea, the butter clam, has only concentric sculpture and the shell gapes slightly at the posterior end.  Protothaca tenerrima is uncommon in protected bays and in sandy mud.  Its hinge ligament is nearly half the shell length and it grows as large as 8 cm.  The cockle Clinocardium nuttallii is a similar shape and has similar color patterns but it has strongly serrated ventral margins to the shell and the radial ribs are much stronger than in P. staminea.
Note:  Mercenaria mercenaria, an Atlantic species, looks and keys very similarly to Leukoma staminea and is also commonly sold in supermarkets.  They even have the fine serrations on the inside of the ventral margin of the valves.  These Mercenaria can be distinguished from Leukoma by the fact that Mercenaria usually has few radial ridges on the outside of the shell while Leukoma typically has well-developed ones.

Geographical Range:  Aleutian Islands, Alaska to southern Baja California

Depth Range:  Lower half of the intertidal down to 10 m depth

Habitat:  In stable sand, packed mud, or gravel-clay mixtures in protected areas, usually buried less than 8 cm below the sediment.  Sometimes found in gravelly sediments among rocks on the open coast.  Occasionally found in empty burrowing clam holes subtidally on the outer coast; in that situation they have raised, concentric lamellae on their shell.

Biology/Natural History:  This common clam is not a true cockle but is sometimes called a rock cockle because it is similarly shaped and has (fainter) radial ribs like some cockles (see Clinocardium nuttallii).  It is often harvested and sold for food, though it is is susceptible to paralytic shellfish poisoning.  Often contains larval tapeworms in large numbers (which cannot infect humans but do infect the bat stingray).  In quiet places such as Hood Canal it often grows so abundantly that shells are nearly touching one another.  The species cannot dig fast so is not found in unstable sand.  Predators include oyster drill snails such as the leafy hornmouth snail Ceratostoma foliatum and moon snails such as Euspira lewisii, Octopus such as Enteroctopus dofleini, sea otter, and the crabs Metacarcinus magister and Cancer productus.  Pacific staghorn sculpins nip the extended siphons.  Spawns during the summer in British Columbia and Alaska, and grows slowly (to only 2.5 cm in 2nd year, or even more slowly in Alaska).  May hybridize with other species such as P. tenerrima and Venerupes philippinarum.  The annual growth lines in the shell are distinct.  May live 8-16 years.

Dudas et al. (2005) found that the common local cancer crabs Metacarcinus magister (Dungeness crab) and Cancer productus (red rock crab) preferred the thin-shelled introduced varnish clam Nuttallia obscurata to the thicker-shelled clams Leukoma staminea and Venerupis philippinarum if access to all was equally easy.  However, Nuttallia obscurata typically lives deeper in the sediment than do Leukoma staminea or Venerupis philippinarum.  If they had to dig for them, Metacarcinus magister still ate more Nuttallia obscurata than it did of the other clam species, but C. productus' preference switched to Leukoma staminea and Venerupis philippinarum.

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Dichotomous Keys: (most key the species as Protothaca staminea)
  Allen, 1976
  Carlton, 2007
  Fitch 1953
  Flora and Fairbanks, 1966
  Kozloff 1987, 1996
  Smith and Carlton, 1975

General References:
  Brusca and Brusca, 1978
  Harbo, 1997
  Harbo, 1999
  Hinton, 1987
  Johnson and Snook, 1955 (as Paphia staminea)
  Kozloff, 1993
  McConnaughey and McConnaughey, 1985
  Morris, 1966
  Morris et al., 1980
  Niesen, 1994
  O'Clair and O'Clair, 1998
  Ricketts et al., 1985
  Sept, 1999
  Snyderman, 1988

Scientific Articles:
Dudas, Sarah E., Iain J. McGaw, and John F. Dower, 2005.  Selective crab predation on native and introduced bivalves in British Columbia.  Journal of Experimental Marine Biology and Ecology 325:1 pp 8-17

Web sites:
  Washington Dept of Fish and Wildlife clam page

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

Leukoma staminea has short siphons which are fused all the way to the end.  The tips are black.  The dark wispy material accumulating near the excurrent siphon in the individual to the right is pseudofeces.

Authors and Editors of Page:
Dave Cowles (2007):  Created original page