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Soft Shell Clams                        Mya arenaria  

Clams

 

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Anatomy

 

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Ark Clams

 

Soft Shell Clams

 

Soft Shell Clam                                               Mya arenaria

The Latin word "Mya" translates into "a sea mussel" and "arena" translates into "sand."

Depending upon which website you visit, they are spelled softshell, soft shell or soft-shell

The soft shell clam is a bivalve mollusk with a thin, oval, elongated shell.  The shell is chalky white with a thin, parchment-like covering that varies in color from brownish to yellowish to gray.

Soft shell clams are found buried in mixtures of sand/mud and mud/gravel where salinity is reduced by freshwater runoff and seepage.

Soft shell clams can tolerate a variety of salinities (5-30 ppt), which makes them well adapted to estuaries. They can live in areas of low dissolved oxygen for short periods of time. Soft shell clams can often withstand below freezing temperatures.

Like all other bivalves, soft shell clams are filter feeders extracting their food (e.g., phytoplankton) from the water column. Soft shell clams have two tubes, called siphons, that work together to strain out food particles from the water column. Water is drawn in through one siphon (incurrent), passed over the gills where food particles collect, and ejected out through the other siphon (excurrent).

Fun Fact - an adult soft shell clam can filter up to four liters (1.06 gallons) of water per hour

Both siphons are enclosed in a leathery membrane.
When closed, the shells gape and two siphons protrude from the posterior end.  (image to the left)
Left valve has a spoon-like depression at the hinge which allows for the fact that the siphons cannot be withdrawn completely into the shell when closed.

Soft shell clams can grow to about 3 to 4 inches.  This is the length of the shell not including the protruding siphons.

Fun Fact - adult soft shell clams can be buried a foot or more under the sediments.

Reproduction  -Soft shell clams are capable of reproduction after their first year of life. 

They reproduce by spawning, similar to the hard clam <see more details>

Spawning is triggered by the increase in water temperature. Once the eggs are fertilized, free swimming larvae develop within a few hours.

Despite their free swimming abilities, they are still susceptible to currents, winds and wave action that can disperse them great distances from the site of fertilization.

The larval period generally takes one to three weeks but is greatly influenced by water temperature.

Eventually larvae metamorph into the juvenile stage and resemble small adults.

Juveniles crawl along the bottom sediments looking for suitable substrates. Once they find a suitable substrate (good food resources, low predation and low wave action), they dig into the sediments with their muscular foot.

While small, they can re-emerge and search for other suitable substrates. However, when soft shell clams become larger, the remainder of their life is spent beneath the sediments in relatively the same location with minimum mobility.

Fun Fact - Maryland exports roughly 90% of Chesapeake Bay's harvest to New England


Predators Animals that eat soft shell clams are quite numerous and include several species of crabs including the blue crab (Callinectes sapidus) and horseshoe crab (Limulus polyphemus), snails, starfish, fish such as killifishes (Fundulus spp.), and waterfowl such as black ducks (Anas rubripes).

Description Soft shell clams have thin brittle shells and a distinguishing leathery tube that encases their well developed and retractable siphons. The elliptical white shell has a spoon shaped depression inside the left valve at the hinge, while the other valve has a projecting tooth that fits into the depression. Soft shell clams can live up to 12 years in Massachusetts.

Other facts:
When disrupted, soft shell clams eject a spurt of water and withdraw to a safer depth in the sediments. This squirting behavior has earned them the nickname "piss clam."
Unlike most other clams, the soft shell clam's siphons cannot completely retract into the clam's shells.
Preyed upon by diving ducks, cownose rays and many other Bay creatures

 



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