Five-Hole Sand Dollar, Keyhole Urchin
Phylum: Echinodermata, Class: Echinoidea, Order: Clypeasteroida, Family: Mellitidae, Genus: Mellita, Species: M. quinquiesperforata · Mellitidae (Sand Dollar family) · Echinoid (Urchin/Test); Non-mollusk. Shape: Disc-like, flattened, sub-pentagonal.
Species
Mellita quinquiesperforata
Shell Type
Echinoid (Urchin/Test); Non-mollusk. Shape: Disc-like, flattened, sub-pentagonal.
Family
Mellitidae (Sand Dollar family)
Size
Approximately 2.5 to 3 inches in diameter. This specimen is mid-sized; adults typically range from 2 to 4 inches.
Color & Pattern
Overall grayish-tan to bleached white color. It features a five-rayed 'petaloid' pattern on the dorsal surface. Darker silt/sand is visible within the lunules and grooves. The original live color (typically brown or lavender) of the spines has been lost, leaving the bare calcium carbonate test.
Rarity
Very Common. While whole specimens are prized, they are one of the most frequently encountered echinoderm fossils/tests on the US East Coast.
Habitat
Shallow marine waters, typically intertidal to subtidal zones. Prefers sandy substrates where it can bury itself just beneath the surface.
Geographic Range
Western Atlantic from the coast of Virginia south through the Gulf of Mexico and Caribbean to Brazil. Very common find at Holden Beach, NC.
Description
An iconic disc-shaped marine skeleton (test). The specimen shows five distinct elongated perforations called lunules and a central star-like flower pattern (petalodium) which housed the respiratory tube feet. The surface is covered in microscopic tubercles where tiny spines once moved, and the edges are slightly thickened.
Key Features
Presence of exactly five elongated keyhole-shaped lunules; flattened profile; central petaloid ambulacra; sub-pentagonal outline with a slightly notched posterior.
Collector Value
Commonly collected but high sentimental value for beachcombers. Commercial value is low ($1-$5) due to abundance, though perfectly white, unbroken large specimens are more sought after. Local regulations in NC often permit collection of skeletal remains but prohibit taking live (fuzzy/dark) ones.
Condition Notes
Good. The test is mostly intact, which is desirable as they are very fragile. There is some minor chipping/wear on the right-most lunule and along the edges. It is naturally sun-bleached but retains good sculptural detail.
Interesting Facts
Despite looking like shells, these are related to sea stars and sea urchins. The 'holes' help prevent the sand dollar from being lifted by wave action (like a wing) and help move food to the mouth on the underside. In Christian folklore, they are known as 'Holy Coins' or 'Mermaid Pennies'.
Ecological Role
Suspension feeders that process organic matter in the sand. They serve as a food source for bottom-feeding fish and crabs. They are sensitive to water quality and serve as bioindicators for sandy-bottom ecosystems.
Similar Species
Mellita isometra (virtually identical and often the specific species found in NC/SC), Leodia sexiesperforata (Six-hole Sand Dollar - has six lunules).
Beach Finding Tips
Best found at low tide, especially after a storm. Look in the 'wash' areas or shallow tide pools. They are often buried just under a thin layer of sand; look for a tell-tale circular outline or a slight 'bump' in the wet sand.
Notes
Holden Beach, NC