Keyhole Urchin / Sand Dollar (often referred to as 'mermaid's coins' or 'fairy money')
Phylum: Echinodermata, Class: Echinoidea, Order: Clypeasteroida, Family: Mellitidae, Genus: Encope, Species: Encope emarginata · Mellitidae (Keyhole urchins and flat sand dollars) · Echinoderm test (internal skeleton/shell), disc-shaped, whole tests
Species
Encope emarginata or similar Mellitidae species (confidence level high for family, moderate for exact species due to small scale)
Shell Type
Echinoderm test (internal skeleton/shell), disc-shaped, whole tests
Family
Mellitidae (Keyhole urchins and flat sand dollars)
Size
Approximately 0.5 inches (1.5 cm) in diameter, which is quite small and juvenile for this species; typical adults range from 2 to 4 inches.
Color & Pattern
Chalky white and sun-bleached due to weathering. Living specimens are typically velvety brown, purple, or greenish-grey, covered in tiny movable spines.
Rarity
Common to Very Common, though finding intact miniature specimens like these is a delightful treat for beachcombers.
Habitat
Shallow subtidal and intertidal zones, sandy or muddy bottoms, often half-buried in the substrate in calm coastal waters or protected bays.
Geographic Range
Warm temperate to tropical waters worldwide, with specific species found along the Atlantic, Pacific, and Gulf coasts of the Americas.
Description
These charming, miniature disc-shaped tests exhibit the classic flattened profile of sand dollars. The upper surface displays a distinct, delicate petaloid (flower-like) pattern of five pores used for respiration. The smooth, chalky white texture results from wave action washing away the velvety spines and organic material of the once-living echinoderm.
Key Features
Flattened circular or slightly petaloid test, the presence of the dorsal five-petal star pattern (petaloid), and the central positioning of the mouth on the underside.
Collector Value
Low commercial value, but high sentimental and aesthetic value for beachcombers and crafters. They are frequently collected as souvenirs rather than bought.
Condition Notes
Fair to Good. These are bleached, sun-dried tests (skeletons) rather than living animals. They appear mostly intact despite their tiny size, though they are fragile and susceptible to crushing.
Interesting Facts
Sand dollars are closely related to sea urchins and starfish. The holes or notches found in some species (hence 'keyhole urchin') help them stay anchored in shifting sand against strong currents.
Ecological Role
Sand dollars play a crucial role in marine benthic ecosystems by bioturbating (churning and oxygenating) surface sediments as they feed on organic detritus, microscopic algae, and detrital particles.
Similar Species
Other species within the order Clypeasteroida, such as Mellita quinquiesperforata (Five-holed keyhole urchin), which can be distinguished by the specific number and shape of lunules (slots) on the margin.
Beach Finding Tips
Look along sandy beaches at low tide, particularly near sandbars or lagoons. Gently sift through fine wet sand or check the wrack line where light, buoyant dried tests wash ashore.