Nuttall's Cockle          Clinocardium nuttallii



The Puget Sound cockle called Nuttall's Cockle, or the Heart Cockle for it's heart-like shape, is one of our more interesting clams.  Unlike other clams that live deep in the sediment to avoid predators, the cockle lives just under the surface using very short siphons to suck in plankton and oxygen.  This exposes it to gulls, crabs and large sea stars.  However it has several adoptions to help it avoid being eaten by gulls who drop it on hard surfaces or by red rock crabs using strong claws.  The first is a thick shell that is heavily ribbed giving the shell strength to resist breakage. Also the margin of the ribs are wavy so the shell halves interlock keeping the shell margin from slipping when dropped or squeezed.   For protection from sea stars, the outer lip of flesh around the margin of the shell sports tiny tentacles and eyes that are used to detect nearby movement and chemicals.  This allows the clam to sense and then avoid the sunflower sea star or the pink short-spined sea star by using it's well developed foot to flip away.


The cockle can be found in muddy sand to pure sand in sheltered conditions.  Areas with more muddy sediment that supports eelgrass can also have high populations.  Their vertical range is from the mid intertidal to around a minus 100 ft.  They have been found from Japan and the Bering Sea south to Southern California.  Similar species are found worldwide where they are often used for human food.


They can live for a long time, between 15 to 19 years, based on counts of the prominent growth rings of the northern variety.  The rings cease to be formed during the winter when the cockle greatly reduces feeding efforts.  They mature by their second year in Puget Sound and spawn in July and August.  This 3.5 inch specimen, which has at least several growth rings, could grow to a maximum of 5.5 inches.


Finally another interesting feature is that they may contain a small commensal pea crab inside the mantle cavity that feeds on material strained out of the incurrent water stream by the clam's gills.