Excentric Sand Dollar    Dendraster excentricus



This well known inhabitant of sandy beaches can be found in the lower intertidal zone and subtidal area in Puget Sound.  It ranges from Alaska to Baja California.  The excentric sand dollar, also called the pacific or west coast sand dollar, is a member of the major group of animals (called Echinoderms) that includes sea stars, brittle stars, sea cucumbers, feather stars, and it's close relative the sea urchin. You can think of the sand dollar as being a flattened sea urchin.  


If you look closely at the animal's surface you will find short spines and tube feet which give the living animal a dark purple color.  Most beach goers have seen only the white skeleton, called a test, with it's five-pointed star pattern on the upper surface.  This star pattern reflects the underlying radial symmetry of this sea star relative.  The little holes that outline the star pattern are for the respiratory tube feet.  Excentric (or eccentric) referring to the off center star pattern is the basis for the species name.


This 3 inch specimen can grow up to 4 inches and is about 1/4 inch high and live for up to 13 years.  They are eaten by starry flounder and the pink short-spined sea star.  You may find the living animal buried during low tide, reappearing as the tide comes in.  Subtidal individuals will lie flat on the surface in exposed areas, but when sheltered will partially burrow and tip on their sides.  Tube feet help grab detritus and diatoms which are moved along by cilia to the mouth.  Sand particles come along for the ride but are discarded by the adult.  However, juveniles retain heavy sand grains in their stomachs as a sort of weight belt to keep them from being washed away.