Sea Biscuit (also known as the Inflated Sea Biscuit or Heart Urchin)
Phylum: Echinodermata; Class: Echinoidea; Order: Clypeasteroida; Family: Clypeasteridae; Genus: Clypeaster; Species: rosaceus · Clypeasteridae (Sea Biscuit family) · Echinoid (Urchin skeleton/test). Not a true mollusk shell. Shape is ovoid and highly inflated (dome-shaped) with a flat underside.
Species
Clypeaster rosaceus
Shell Type
Echinoid (Urchin skeleton/test). Not a true mollusk shell. Shape is ovoid and highly inflated (dome-shaped) with a flat underside.
Family
Clypeasteridae (Sea Biscuit family)
Size
Approximately 2-3 inches in length. This is an average-sized specimen; adults can reach up to 5 inches. It is notably thick and bulbous compared to flat sand dollars.
Color & Pattern
Bleached white to creamy tan. In life, they are covered in short brown/reddish spines. After death, the spines fall off, leaving a white calcium carbonate test. The top features a distinct five-petaled flower pattern (ambulacra) made of tiny pores.
Rarity
Common. Beachcombers frequently find these washed up after storms in Florida and the Caribbean, though finding them perfectly intact is less common than finding fragments.
Habitat
Shallow tropical waters, typically found in seagrass beds (Thalassia) or sandy bottoms near coral reefs. They are marine animals that live at depths of 1 to 50 meters.
Geographic Range
Western Atlantic Ocean, including the Caribbean Sea, Gulf of Mexico, Florida, and the Bahamas down to Brazil.
Description
This is a robust, dome-shaped calcium carbonate skeleton of a sea urchin. It features a characteristic five-leaf clover pattern on the dorsal side. The texture is finely granular, covered in tiny tubercles where spines were once attached. The underside (not fully visible) is flat with a central mouth (peristome).
Key Features
Inflated, thick profile (unlike flat sand dollars); five-petaled pore pattern on the top; porous, lightweight structure; ovoid shape.
Collector Value
Low to Moderate ($2 - $10 USD). They are popular with beginner collectors and for home decor, but since they are common, they only hold high value if they are exceptionally large or still retain their natural brown spine covering.
Condition Notes
Good to Fine. The specimen appears largely intact, though it has been naturally sun-bleached to a white color. There is some minor surface erosion typical of a beach-find, but the petaloid pattern remains clear.
Interesting Facts
While they look like rocks, these were living animals. They use their tiny spines to 'walk' and burrow through the sand. They are related to starfish and sea cucumbers. Historically, they have been used as curiosities and in coastal folk art.
Ecological Role
Detritivores; they play a vital role in 'tilting' the sea floor, consuming organic matter within the sand and recycling nutrients back into the ecosystem. They are prey for large gastropods like the Triton's Trumpet and certain fish.
Similar Species
Moira atropos (Heart Urchin), which has deeper indentations; and various species of Sand Dollars (Mellita), which are much flatter and have holes (lunules).
Beach Finding Tips
Look along the high tide line after a storm or strong offshore winds, particularly in Florida or the Bahamas. They often get trapped in seagrass clumps washed ashore.