Macoma (Heteromacoma) nasuta (Conrad, 1837)

Common name(s): Bent-nosed clam, Bent-nose Macoma

Synonyms:  Macoma tersa, Macoma kelseyi
Phylum Mollusca
 Class Bivalvia
  Subclass Heterodonta
   Order Veneroida
    Family Tellinidae
Macoma nasuta from Padilla Bay, WA. Anterior is to the right.
(Photo by: Dave Cowles, July 2005)
Description:  Like all members of family Tellinidae, this clam has a rounded shell with neither valve very flat nor very inflated, and the anterior and posterior ends are shaped differently.  There are two adductor muscle scars of similar size on each valve.  The umbones are near the middle of the dorsal side.  It has no radial ribs.  The hinge has a true hinge plate with two cardinal teeth on both valves (photo).  The hinge ligament is mostly external.  The valves have a pallial sinus and a continuous pallial line.  The valves gape only slightly, if at all, at the posterior end.  The siphons are long and separate (photo). Macoma nasuta has a long hinge ligament, no lateral teeth on its hinge plate, is less than twice as long as high, and the posterior end of both valves is bent to the right (photo)(photo).  The pallial sinuses are large, extend to beneath the anterior adductor muscle scars, and are very close to the pallial line ventral to them (photo).  Length to 11 cm but usually not more than 6 cm.  Shells are chalky white and usually unstained, with some grayish-brown periostracum.

How to Distinguish from Similar Species:  This is the only clam in this area that has the posterior ends of the valves bent to the right.

Geographical Range:  Kodiak Island, Alaska to Cabo San Lucas, Baja California, Mexico

Depth Range:  Low intertidal to 50 m

Habitat:  Buried in mud flats; also found in gravel, sand, or muddy clay

Biology/Natural History:  This common clam lies on its left side instead of vertically, at a depth of 10-20 cm.  It rocks back and forth while digging.  The siphons extend out the right side and up to the surface, which are well accomodated by the twist to the right of the shell.  The siphons are used to suck debris from the surface of the sediment like a vacuum cleaner.  The clams digest mainly diatoms and some flagellates from the sediments.  They ingest large quantities of sediment but reject 97% of it, producing copious pseudofeces (photo).  Hinton says the clam moves to another location when the sediment in an area has been thoroughly picked over.  Predators include the moon snail Polinices lewisii.  The clam was an important food of the coastal Indian tribes and to Chinese immigrants in San Francisco but is little used commercially today because of the debris that is usually in the gut.  This species is very hardy and can be found in areas that have very poor circulation, and can live in very soft, silty mud.  The pea crab Pinnixa littoralis or P. faba may live in the mantle cavity, as may the Nemertean worm Malacobdella grossa.  The species spawns in early summer in Oregon.

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Dichotomous Keys:
  Flora and Fairbanks, 1967
  Kozloff 1987, 1996
  Smith and Carlton, 1975

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

Scientific Articles:

Web sites:

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

The posterior end of the shell (left in the photo above) is bent to the right.  Many individuals are bent more than this one is.  Photo by Dave Cowles, July 2005

Very bent nose
The "nose" of this individual, about 3.5 cm long, is bent even more. Photo by Dave Cowles, July 2020

This species has long siphons which it can extend from the posterior end of the shell and up through several cm of sediment to the surface.
They look creamy white when extended but look more orange when they are retracted.
This species sucks in sediment, digests out some diatoms and flagellates, and rejects the majority of the sediment leading to copious production of pseudofeces, as seen in the photo.  The nose is bent because the clam lives in this position-on its side, so must extend the siphons up and to the side to reach the sediment surface.
Photo by Dave Cowles, August 2005
Hinge teeth
A closeup of the hinge teeth. There are two cardinal teeth on both valves. The tooth on the right is bifid. Photo by Dave Cowles, July 2020

Pallial line
A view of the pallial line and pallial sinus. The posterior (siphon) end of the clam is to the left. Notice how the pallial sinus is so deep that it penetrates as far anterior as the anterior adductor muscle scar. Photo by Dave Cowles, July 2020

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