Encope: The Notched Sand Dollars

What Encope Is

Encope is a genus. Not a species, not a common name: a genus, holding the sand dollars that are cut into at the rim.

The addresses above it run like this. Phylum Echinodermata. Class Echinoidea, which is the sea urchins. Inside Echinoidea, the irregular urchins: the flattened ones with a front and a back, rather than a globe with no such axis. The order is Clypeasteroida, and it also holds Mellita, the five-slotted sand dollars, and Clypeaster, the sea biscuits. Encope is a third address in the same neighborhood, and it is the one most people have never been told about.

There are several species in the genus. On a Florida beach the one worth knowing by name is Encope michelini.

Notched at the Rim, Not Slotted Through the Test

Two words carry this page, so get them straight first.

A lunule is an opening that passes through the test and is enclosed by test on every side, the way a buttonhole is enclosed by cloth. A notch is an indentation cut in from the margin, open to the outside, the way a bite is taken out of a cookie.

A Mellita is built with lunules: the outline of the disc is an unbroken curve and the slots sit inside it. An Encope is built with notches, so the outline itself turns inward, runs around the opening and comes back out to the rim. That is a difference in how the animal is put together, not a difference in how much surf it has been through.

The second difference you feel rather than see. An Encope is heavier and thicker. A Mellita test is roughly a millimeter of fused plate and handles like a wafer. An Encope has substance to it. For the five-slotted animal in full, including why the Gulf one is Mellita tenuis and not the Atlantic name nearly every source prints, see our Mellita page, and for the parts of either animal named one at a time, our anatomy page.

Encope michelini and the Notched Sand Dollar

Encope michelini is the species a Florida beachcomber is most likely to meet, and the one carrying a common name with an institution behind it. The US Fish and Wildlife Service lists its common name as the Notched Sand Dollar. That name is descriptive, it is accurate, and unlike most sand dollar vernacular you can follow it back to a body that publishes lists.

It occurs on both Florida coasts and Gulf-wide. That is wider than people expect, and it changes how much work locality can do for you. With a five-slotted disc, range is a real argument, because the Gulf species and the Atlantic species live on opposite sides of the state. With a notched disc that argument is not available.

What that buys you is discipline. If the map cannot narrow it, the specimen has to.

How to Tell a Notch From a Lunule on a Worn Test

This is the part worth carrying to the beach, because the tidy definition above stops being tidy the moment a test has spent a season in the surf.

Start with the wrong method so you can stop using it. Holding the disc up to the light settles nothing here. A lunule passes light and a notch passes light. Counting bright spots is how a person talks themselves into something rare when they are holding an ordinary thing with a piece missing.

The right method is to trace the outline. Lay the disc flat on your palm, follow the edge all the way around with your eye, and watch what the boundary does.

• If the boundary runs smoothly past the opening and the opening sits inside it, that is a lunule.
• If the boundary itself detours inward, goes around the opening and returns to the rim, that is a notch, and you may be holding an Encope.

Counting settles the other animals on this coast. Five enclosed slots means Mellita. Six means Leodia sexiesperforata, the six-holed keyhole urchin, and there the count is the whole test. Counting is not the test here. We are not going to give you a notch count for Encope, because we have not verified one against a primary source, and a page that spends its length telling you not to repeat unchecked claims does not get to make one on the way out the door.

The Trap: A Broken Lunule Looks Exactly Like a Notch

Here is the commonest way a worn Mellita gets promoted into something rarer.

A lunule sits with a thin bridge of test between it and the margin, and that bridge is the narrowest, most exposed material on the whole disc. Break it, and the slot opens to the rim. What you are holding now looks, in outline, like a notched sand dollar.

So do not read the shape. Read the edge.

• A finished margin, the kind the animal built, matches the rest of the margin: same surface, same rounded finish, the plate pattern running up to it in order.
• A fracture looks like a fracture: a rawer, brighter, more granular edge where the internal structure of the test is exposed, often with a small step or a snapped point at one end or both, and no continuity with the rim on either side.

A hand lens settles most cases in seconds. So does the rest of the disc. Damage is usually a one-off and structure is not, so compare the openings against each other: if one is ragged and open to the rim while the others sit enclosed, you have a broken Mellita, not a puzzle.

Weight, Thickness and Where They Stop Helping

The heft check is genuinely useful, and it is also the one people over-trust, so here it is with its edges showing.

Encope is the heavier, thicker-tested animal. Pick both up on the same afternoon and you will not need convincing. That thickness is why an Encope feels solid where a Mellita feels like something you could break by closing your hand, which, with a Mellita, you very nearly can.

Now the limits. We are not going to hand you a thickness in millimeters or a weight in grams, because we have not verified either. Heft is a comparison, and a comparison needs two things in hand. It is not a reading you can take off a single object sitting on a table. Thickness also does not mean indestructible: it means a test that takes more handling before it goes. What actually fails in a sand dollar, and when, is the subject of our why they break page.

"Inflated" Belongs to a Sea Biscuit

Now the naming mess, starting with the misnomer that is easiest to disprove.

You will find Encope sold and captioned as the "inflated sand dollar". The word inflated is not an Encope name. The Florida Fish and Wildlife Conservation Commission uses it for Clypeaster rosaceus, the inflated sea biscuit: a different genus, a different body, and not a sand dollar at all.

A sea biscuit is thick and domed rather than flat, and it is not built with lunules. Clypeaster rosaceus and Clypeaster subdepressus, the flat sea biscuit, sit in the same order as the sand dollars, so they are close kin, and they are the animal most often mistaken for a giant sand dollar. Our sea biscuits page is the full treatment.

How the word migrated is not hard to picture. An Encope is thicker than the sand dollar most people know, somebody reached for a word meaning thickened, and found one already attached to a different thick echinoid. Plausible story, wrong name, wrong animal.

"Arrowhead" Is a Nickname Wearing a Name's Clothes

The second bad name is harder to disprove only because it never claimed to be anything in the first place.

"Arrowhead sand dollar" is a vendor nickname, applied inconsistently across several Encope species. That inconsistency is the tell. A name that lands on more than one species, differently depending on who is selling, is not identifying anything. There is no type specimen behind it, no register entry, no agency list, no published description. It is a shape word that sells well.

None of this is a reason to sneer at common names. They are how nearly everybody meets an animal for the first time. "Notched Sand Dollar" is a common name too. The difference is that you can follow it back to US Fish and Wildlife Service and find out what it is attached to, and there is nowhere to follow "arrowhead" back to. The rule is short: never write a nickname on a label where a determination belongs.

How a Dealer Label Turns Into a Fact

The mechanism is worth understanding, because it is the same one behind most of the wrong shell facts on the internet, and nobody in the chain has to be dishonest for it to work.

A dealer buys a lot of material and needs to describe it. The description has to be short, appealing and consistent across a bin, and it does not have to be right, because nothing checks it. The bin gets a label. The label gets photographed with the specimen. The photograph goes into a listing. The listing gets quoted, or scraped, or used as a reference image by somebody writing a post. That writer prints the label as the common name. The next writer finds three pages using it and reasonably concludes it is established usage. At the end of that chain, a word invented for a bin is cited as though a taxonomist put it there.

A dealer label is not a source. The test is one question: can you follow the name back to a register, an agency list, or a published description? If you can, use it and say where it came from. If you cannot, it is a nickname, and it belongs in quotation marks or nowhere.

The warning extends to the specimen. A purchased test carries no locality, no date and no collector, which makes it a decoration rather than data, and it may not have come from Florida at all. Shells brought into the United States from abroad have to be declared to US Fish and Wildlife Service, protected or not, which is a fair reminder of how routinely this material crosses a border before it reaches a shelf.

The Taxonomic Question This Page Will Not Settle

There is a live disagreement inside this genus, and you should know it exists before you write a species name on anything.

The World Register of Marine Species currently lists Encope aberrans as a junior synonym of Encope michelini, which is to say it treats them as one species under the older name. Coppard and Lessios (2017, Scientific Reports) used molecular phylogenetics, found the two to be monophyletic sympatric species that diverged around six million years ago, and explicitly rejected that synonymy.

We are not going to pick a winner. A global taxonomic register and a peer-reviewed molecular study disagree, both are serious, and the honest position for a shelling company is to name both and stay out of it. What that argument actually is, what a synonymy means, what a register does and what molecular work adds to it, is the entire subject of our Encope problem page, and that is where it gets worked through.

The consequence for you is small and clear. A question still open at the specialist level is not one a bleached test on a beach is going to close.

Where They Live

Sand, and specifically the top layer of it. Sand dollars work themselves down into the surface of a sandy bottom rather than crawling across it, moved by spines and tube feet together, and they can sit edge-on into a current instead of presenting a flat face to the flow. Depth varies by species, from shallow water out to considerable depth, and we are not going to invent a depth range for Encope that we have not checked.

They are also not scattered individuals. Sand dollars live in dense aggregations, and in some populations those beds reach densities of hundreds per square meter. The bare disc in your hand came out of a crowd somewhere offshore, and a bed is not something to walk through. Our pages on sand dollar beds and how they move go further into both.

How One Ends Up at Your Feet

An Encope on the wrack line has been through a process, and the process explains most of what you are looking at.

The animal died offshore. The spines, short and dense and movable in life, came away. The pigment went, which is why the disc is white: white is what time does to a test, not what the animal was. Then it traveled, and traveling is the part people underestimate. Shells and tests sort themselves hydraulically in the swash zone, gather along the wrack line, and pile up in shell bars, on spits, and at the inside bends of passes. Where you found it is where the water put it, which is not where it lived.

It is reasonable to expect a thicker test to arrive intact more often than a thin one, and we would rather show you that as reasoning than dress it up as a measured fact. We have no published comparison to cite, so treat it as a plausible expectation and not a finding.

Alive, Dead, or Just Stained

Before you pocket anything, work out what you actually have.

A living sand dollar is dark: brown, purple, gray or green, and covered in dense short movable spines that move if you watch them. The white disc is the bleached test, the internal skeleton of an animal that died some time ago. If what you found is still dark, set it on your palm for a minute. A live animal stains skin yellow with echinochrome, a harmless pigment, and that is the fastest field test there is. Our echinochrome stain page covers what it does and does not tell you.

One complication belongs right here. Not every dark test is a live animal. Black or gray staining is usually iron sulfide picked up from burial in oxygen-poor sediment, and it happens to recently dead material as readily as to old, so black does not mean fossil either. Our fossil sand dollars page takes that apart.

The rule on our boat is empty shells only, and that is our own house rule rather than a statute we are quoting at you. It happens to line up with the law on City of Marco Island beaches, where city code section 54-36(o) prohibits live shelling. Florida statute 379.101(34) is why live and empty are different questions: it counts living echinoderms as saltwater fish and expressly excludes nonliving shells. Read FWC's sea shell collecting page rather than anyone's summary of it, ours included.

How to Record One Honestly

There is an established convention for a find you cannot take to species. It is used in real collections and it costs you nothing.

• Encope sp. means genus Encope, species undetermined. That is a complete and respectable identification.
• Encope cf. michelini means this compares with Encope michelini. The "cf." is the Latin confer, compare, and it records which way you leaned without claiming you settled it.
• Encope michelini, written bare, is a determination. Write it only if you made one.

Around the name, record observations rather than conclusions. The date. The beach, and the most specific position you can give. Whether the animal was alive or already a bare test. Whether each opening broke the outline or sat enclosed inside it, and whether its edge looked finished or fractured. Whether the test was whole.

Photograph both faces before it breaks, because eventually it will. The underside is the face people skip, and it carries the mouth, the food grooves and the anal opening near the margin. iNaturalist is a good place for a second opinion, and genus-level identifications are normal there. What you must not do is quietly upgrade a guess: once "probably michelini" is copied onto a card as "michelini", the doubt is gone and the record is false.

Keep it away from acidic vapor, which some woods and cardboards give off and which causes Byne's disease. Our shell collecting page has the rest. To check a name yourself, use the World Register of Marine Species and not MolluscaBase: a sand dollar is not a mollusk, so an empty search there means the wrong register, not a bad name.

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 here.