The Pacific, West Coast, or Eccentric Sand Dollar
Dendraster excentricus
Photo by Mary Jo Adams Copyright 2004
And an Adventure in Nature it proved to be.
A very low-tide beach walk at Camano Island State Park on 7/2/04 was a sea-life-filled-one-some extremely interesting species-species again seldom seen on our beaches.
Neither my co-guide Tom Eisenberg nor I had ever seen live sand dollars on our island beaches. But sure enough, a small aggregation was lying down there in the very lowest intertidal zone of the park beach that day. We were delighted. All these marvelous species for our group's eyes only!
No, we're not talkin' here the off-white and at times bleached Sand Dollar shells sold in shore-side stores, nor the empty test or shell remains easily found after a high surf at a sandy beach such as Cannon Beach . No, we're talkin' the real McCoy-the live critters. And how very different the live specimens are from the naked tests. So different that it would be quite possible to not make an immediate connection between the two.
Northwestern marine writer Rick M. Harbo says, "Sand Dollars have been called flattened irregular sea urchins with reduced spines which typically incline backwards rather than standing erect."
Related to urchins they are-as well as sea stars-members of the phylum Echinodermata-creatures with usually five-parted radial symmetry and externally evident calcerous spines, scales, or tubercles. Tiny 1/16 " spines, indeed, are found both top and bottom-side-useful for burrowing and slow locomotion-tube feet as well.
The dollars we encountered were a rather deep purple in coloration, although they can be grayish or a sort of brownish-red. And texture-wise, some feel the multitudinous, densely packed, abbreviated spines and tube feet give live dollars a somewhat velvety appearance.
A five petal, leaf, or star pattern radially symmetrical, is seen on the upper side of spineless, colorless shells washed ashore. Actually the pattern consists of a series of tiny holes, and from these small holes, in life, respiratory tube feet extend.
Etymologically speaking, the genus name Dendraster means tree or star---excentricus meaning off center-because, if a shell is more closely examined, the five leaf or petal pattern will be found to be a bit, yes, off center.
Diatom and detritus vittles are popular foodstuffs, and on the under or ventral surface of a shell one can see most observable evidence of food tracts where such eats are passed along-brushed along the grooves with the help of small moving hair-like cilia toward the central mouth. In addition to these tracts one can also see the actual mouth opening and a smaller anal opening near the shell's edge.
And although we encounter scant material proof of Sand Dollars being on Camano Island beaches, they are a creature that subtidally, in some waters, can be present in huge numbers-like over 523 per square yard according to biologist/writer J. Duane Sept.
Preferring protected deeper offshore subtidal waters as opposed to higher intertidal or heavy surf situations, dollars often will be found there-half buried in the sand-their upper surfaces slanting in the current's direction.
In such protected waters they have been known to live up to 13 years-although their long lives could be abbreviated-cut short-if they find themselves turned over. For apparently they are unable to then turn themselves dorsal side up, right themselves from such positions, and will eventually die.
Another more frequent cause of Sand Dollars' demise would be predators such as flounders and the big, pink, short spined sea star, Pisaster brevispinus, which we also saw on our adventurous very low tide walk. Pat Nash
Beach Watcher
Class of '94