Sand Dollars of the World

The Same Shape, on Coasts With Nothing to Do With Each Other

Stand on a beach in South Africa and someone will hand you a flat white disc with five petals on it. Same in New Zealand. Same on the cold sand of the North Atlantic, and same on the Pacific side from Alaska down to Baja. The disc sits in a cupped palm the way the one here does, it carries the same five-part figure on its upper surface, and it is called something different in every one of those places.

That is the first job of this page: a tour of the sand dollars a traveler actually meets, each one tied to the coast it lives on and not one inch further.

The second job matters more if you are standing in Southwest Florida. Not one of the species below occurs here. If a disc reaches you with a Florida story attached and one of these names on the card, the story and the name disagree, and the name is the part that can be checked.

The Table: Name, Species, Coast

Read it a row at a time. The first column holds what people actually say, the second holds what the animal is, and the last one is what settles arguments.

Two notes on how to read it. The name column lists only vernacular names we can tie to a source, and plain "sand dollar" does duty across most English-speaking coasts, which is exactly why it settles nothing. The coast column repeats published ranges as published: where one reads oddly, as "New Jersey and Labrador northward" does, that is the range statement and not a typo we tidied up.

Sea biscuits, the genus Clypeaster, are close kin in the same order and are not sand dollars, so they are not in the table. Our sea biscuits page handles them.

South Africa: the Pansy Shell

Echinodiscus bisperforatus is the animal known in South Africa as the pansy shell. That is the association we can state, and it is the one we will stay inside. We are not going to stretch its range across the rest of an ocean for you, because we have not checked it, and an unchecked range is the exact thing this page exists to argue against.

The common name is doing what common names do. It reads the five-petal figure on the upper surface as a flower, then picks a flower with the right number of lobes. Memorable, and it tells you nothing true about what you are holding. That figure is the petalodium, a field of pores for flattened tube feet used in gas exchange. It is a breathing structure, and our five petals page takes it apart properly.

The scientific name is more honest. Echinodiscus is the spiny disc. Bisperforatus reads as twice-pierced, recording how many openings the describer counted. A name is not a specimen, so if one ever ends up in your hand, count the openings yourself. Counting is the one character on a sand dollar a beginner can get right every time.

New Zealand: the Snapper Biscuit

Fellaster zelandiae carries its address in its name. Zelandiae, of New Zealand. It has two vernacular names in circulation there, snapper biscuit and cake urchin, and one animal holding two names is the normal condition of common naming rather than an exception to it.

Where the snapper in snapper biscuit comes from, we are not going to guess. A snapper is a fish, there are several plausible stories about how the fish and the disc got attached to each other, and we have checked none of them. Guessing at an etymology is how a folk story becomes a fact on the internet.

Cake urchin is easier and quietly better. It calls the animal what it looks like on a plate, and it keeps the word urchin in there, which almost no sand dollar name manages. Sand dollars really are urchins. They sit in the class Echinoidea alongside the globular ones, and the case is laid out on our sand dollar versus sea urchin page.

Sea Cookie, Galleta de Mar, and Names That Belong to Nobody

Two more names you will meet, and they behave differently from the two above. Sea cookie and the Spanish galleta de mar are general vernacular across New Zealand, Brazil and Latin America. Neither is the common name of one species. They are what people in several countries call whatever flat disc washes up in front of them.

That is not sloppiness on anyone's part. It is what a vernacular name is. It attaches to a shape, gets used by people with no particular stake in which species produced the shape, and travels wherever the shape does. Galleta de mar covers ground across two continents. A scientific name cannot do that, because a scientific name has a register, a type specimen and a paper trail holding it in place.

So when someone tells you they found a sea cookie, you have learned the shape and nothing else. Line up the whole vocabulary and the joke tells itself: dollar, biscuit, cake, cookie, galleta, which is also a cookie, and pansy, the one flower in the set. Almost every name humans have given this animal is either money or something you eat, and the money one is ours.

The North Atlantic: Echinarachnius parma

Echinarachnius parma is the northern one. The range as published runs New Jersey and Labrador northward, which is to say cold water, and which is to say a long way from here in every sense that matters.

Read what that range does and does not say. It does not say the Gulf of Mexico. It does not say Florida. It does not say the Carolinas. It runs the other direction from us, up the seaboard and past Labrador, and there is no reading of it that touches a sandbar off Marco Island.

Which produces a useful piece of logic. Because the animal does not live here, if you meet this name in Florida you are meeting it on a label rather than on a beach. The mechanism behind that is usually dull rather than sinister: discs get collected somewhere, sold in bulk, shipped, and labeled wherever they land. If one reaches you as Florida material with Echinarachnius parma on the card, one of those two claims is wrong, and the range is the one with a taxonomic register behind it.

The Pacific: Dendraster excentricus, and What Eccentric Means

Dendraster excentricus is Pacific only, ranging Alaska to Baja. It is the sand dollar of the American West Coast and it is not the sand dollar of any coast on the other side of the continent.

The epithet is the good part. Excentricus means off-center, and it is describing the petal figure. On this animal the petalodium does not sit in the middle of the disc. It is displaced toward one end, far enough that the arrangement was worth putting in the name. That is the whole of what eccentric means here: nothing about behavior, nothing about the animal being odd, just a five-petal figure that is not where you would expect to find it.

It is also a good reminder that the petalodium is a structure with a position and a geometry rather than a decoration stamped on the middle of every disc. Where it sits, how far the petals reach, and whether the figure is symmetrical are all real characters. What they are made of and what they do is the five petals page.

The Most Studied Sand Dollar in the World Is Not Ours

Here is why a Florida reader should care about a Pacific animal. Two of the most quoted facts about sand dollars anywhere on the internet were established on Dendraster excentricus, and both get repeated as though they were facts about sand dollars in general.

The first is lifespan. Six to ten years is a defensible general figure for echinoids, and the best-documented case is up to about 13 years, aged from growth rings on the test plates. That case is Dendraster excentricus. No comparable published study exists for Mellita or Encope, which means the age of the animal that made the disc in your hand is genuinely unmeasured. Our lifespan page says so at length.

The second is stranger and better. Larvae exposed to predator cues, fish mucus specifically, clone themselves defensively. That is real peer-reviewed work, Vaughn and Strathmann in Science, 2008, followed by Vaughn in 2009, and it was done on Dendraster excentricus. A Pacific species. Not ours. The finding does not transfer to a Gulf animal just because both are flat and round, and our larval cloning page keeps that line drawn.

So the practical lesson of a world tour is not exotic at all. "Sand dollars do X" is usually shorthand for "one species of sand dollar, on one coast, was measured doing X."

Why the Same Shape Keeps Turning Up

A flat disc, a five-petal figure on top, a mouth in the center underneath, spines and tube feet, worked into the top layer of sand. That description fits animals in South Africa, New Zealand, Labrador, Baja and Marco Island, on coasts with no particular connection to each other.

Part of the answer is inheritance. All of them are echinoderms, phylum Echinodermata, and all of them are class Echinoidea, the urchins. Within that they are the irregular echinoids: flattened, with a front and a back, unlike the globular regular urchins that have no such axis. They came into the problem carrying the same equipment, and the equipment is unusual. Pentaradial adult symmetry. A calcite skeleton of fused plates. A water vascular system driving tube feet. A bilaterally symmetrical larva that becomes a five-part adult.

The other part of the answer is that the problem is the same everywhere. Shifting sand is shifting sand in every ocean. An animal living in the top layer of it has to resist being lifted and rolled, has to move water and fine particles across its own surface, and has to breathe while mostly buried. A thin flat disc answers all three, and it keeps getting arrived at.

Whether any particular resemblance between two of these animals is inherited from a shared ancestor or reached separately is a question for a phylogeny, not for a beach, and we are not going to settle it in a paragraph. What is fair to say is that the shape is not a coincidence.

What a Range Statement Is Actually Telling You

Every row in that table lives or dies on a range, so it is worth being clear about what a range is.

A published range is a statement about where the living animal has been recorded. It is not a statement about where a dead test can end up. Those are two different maps, and the second one is the whole earth, because a test drifts and a box of tests ships anywhere for the price of postage.

Ranges also get revised. They are built from records, records come from people going and looking, and coasts get looked at unevenly. A range extended next year was not a lie this year. It was the best available summary of where anyone had been. That is a reason to cite a register rather than a memory, and to date what you write down.

And a specimen with no locality has no range at all. A disc out of a bin, a craft bag, a resale listing or a relative's shelf carries nothing about where it lived, and no amount of confidence supplies it later. Locality is the one part that cannot be reconstructed, which is why our shell collecting page treats the label as the specimen's most important feature.

None of These Occur in Southwest Florida

Plainly, without hedging, because this is the sentence the page was built to deliver. Echinodiscus bisperforatus, Fellaster zelandiae, Echinarachnius parma and Dendraster excentricus do not occur on a Southwest Florida beach. Not rarely. Not occasionally after a storm. They live on other coasts, and the ranges above are the reason.

What does live here is a short list, and a better one than most visitors expect.

• Mellita tenuis, the five-slotted sand dollar of the Gulf, described from a type locality at Sanibel Island and ranging Louisiana to west Florida. This is the animal on our beaches, and why nearly every source prints the wrong name for it is the subject of our Mellita page.
• Leodia sexiesperforata, the six-holed keyhole urchin, North Carolina to Uruguay, Florida and the Gulf included. Count six slots instead of five and you have settled it in about a second.
• Encope michelini, whose US Fish and Wildlife Service common name is the Notched Sand Dollar. Notched at the rim rather than pierced through, on both Florida coasts and Gulf-wide.
• Clypeaster, the sea biscuits, thick and domed, close kin in the same order, and not sand dollars.

If the name attached to a disc is one of the four foreign species above, that disc did not come off this beach.

What a Wrong Label Is Telling You

Say a shop, a stall or an online listing offers you a sand dollar as Florida material, and the card reads Dendraster excentricus, or the seller calls it a pansy shell. What have you learned?

Probably not that anyone is lying to you. The likeliest explanation is duller. Bulk material moves through wholesalers, arrives with no locality attached, and picks up whatever regional label the shop happens to use. Nobody in that chain necessarily set out to mislead. Nobody in that chain checked, either.

What you have learned is what the rest of that seller's labels are worth. A place that cannot get the right ocean is not a place to take an identification from. You have also learned that this particular disc has lost the one thing that would make it more than an ornament, which is where it came from.

None of that is an argument against buying it. Buy it if you like it. Just write on the box what is actually true: purchased, this date, this shop, locality unknown. In ten years that line will be worth more than a species name nobody verified.

If You Pick One Up Somewhere Else

Two rules travel home with you, and they surprise people.

Everything gets declared. All seashells brought into the United States from abroad must be declared to the US Fish and Wildlife Service. Protected or not, personal or commercial, one disc in a sock or a crate on a manifest. Declaring is not the same as being denied. It is the step that keeps a lawful souvenir lawful.

Getting it on the plane is the easy part. TSA allows clean dry shells in both carry-on and checked bags.

What we cannot tell you is what the law is on the beach where you found it. South African, New Zealand, Brazilian and Canadian collecting rules are their business and not ours, and a page written in Goodland has no standing to summarize them. Ask locally before you pocket anything. Aboard our boat the house rule is empty shells only, and that one we can speak for.

How to Check a World Name Yourself

One trap first, because it catches careful people. MolluscaBase is the right authority for a whelk or a cockle, and it does not cover sand dollars, because a sand dollar is not a mollusk. Echinoderm names live in the wider World Register of Marine Species. An empty search in the mollusk register means you reached for the wrong shelf, not that the name is wrong.

Search the name there, then read the record rather than the headline.

• Status. Accepted, or unaccepted with a pointer to the name that replaced it.
• AphiaID. The stable number for the record. Numbers hold still even when names move.
• Authority and year. Parentheses around the author mean the species was first described in a different genus and has been moved since.
• Distribution. The line that settles every question this page asks.

Vernacular names have no register at all, which is precisely why sea cookie and galleta de mar can drift across two continents without anybody being wrong. For specimens rather than names, the Florida Museum's invertebrate zoology collection is the regional reference, and the rest of the animal is laid out across the sand dollar codex.

If you would rather ask a person than a database, that is what the ride back is for. We run three trips a day out of San Marco Marina in Goodland, and you can reserve a seat.