Sea Urchin Test (Fairy Biscuit, Mermaid Beads)
Phylum: Echinodermata, Class: Echinoidea, Order: Arbacioida, Family: Arbaciidae, Genus: Arbacia, Species: Arbacia punctulata · Arbaciidae (Arbacia Urchins) · Echinoid test (Endoskeleton of a marine invertebrate, roughly spherical to slightly flattened shape)
Species
Arbacia punctulata (or similar small echinoid)
Shell Type
Echinoid test (Endoskeleton of a marine invertebrate, roughly spherical to slightly flattened shape)
Family
Arbaciidae (Arbacia Urchins)
Size
Approximately 0.5 inches (12-15 mm) in diameter, which is typical for small juvenile specimens or smaller species of sea urchin tests.
Color & Pattern
Pure chalky white due to bleaching and loss of spines and outer epidermis. The natural color when alive can range from purple, reddish-brown, to greyish-green.
Rarity
Common
Habitat
Shallow marine waters, rocky shores, coral rubble, seagrass beds, and sandy bottoms from the intertidal zone down to moderate depths.
Geographic Range
Commonly found along the Atlantic coast of North America, from Cape Cod down to the Caribbean and Gulf of Mexico, depending on the exact species.
Description
These delicate, spherical shells are actually the internal skeletons (tests) of sea urchins. Stripped of their spines and skin, the calcium carbonate shell reveals intricate radial symmetry, rows of tiny bumps where spines once attached, and distinct pore pairs.
Key Features
Spherical or flattened calcareous test featuring five-fold radial symmetry, small tubercles for spine attachment, and prominent apical and oral openings at the poles.
Collector Value
Low monetary value, but highly popular among beachcombers and crafters for decorative purposes, jewelry making, and shell displays.
Condition Notes
Good condition. Intact white tests with little to no structural damage, though completely bleached and devoid of spines.
Interesting Facts
Beachcombers often call these 'fairy biscuits' or 'mermaid beads'. In life, the urchin covers itself with bits of shell and algae for camouflage and protection against the sun.
Ecological Role
Sea urchins play a crucial role in marine ecosystems as herbivores that graze on algae, preventing it from overgrowing coral reefs. They are prey for fish, sea otters, and birds.
Similar Species
Keyhole urchins, cake urchins, and various heart urchins (sand dollars), which are flatter rather than globular.
Beach Finding Tips
Look along the wrack line on sandy beaches after storms, or comb through shallow rocky tide pools during low tide.