Mortensen's Cockle (also known as the Egg Cockle)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Cardiidae, Genus: Trachycardium, Species: Trachycardium muricatum · Cardiidae (Cockle family) · Bivalve (two-shelled), whole shell, fan/heart shape
Species
Trachycardium muricatum
Shell Type
Bivalve (two-shelled), whole shell, fan/heart shape
Family
Cardiidae (Cockle family)
Size
Approximately 1.5 to 2 inches in width, which is average for this species. Adults typically range from 1 to 2.5 inches.
Color & Pattern
Pale creamy white to yellowish base color with subtle brownish or yellowish speckles. The colors appear slightly sun-bleached due to beach exposure, showing a uniform light tone across the exterior.
Rarity
Common, frequently found by beachcombers along the Texas Gulf Coast.
Habitat
Shallow subtidal zones to intertidal flats, typically found buried just beneath the surface of clean sand or muddy sand environments. Marine species.
Geographic Range
Western Atlantic Ocean, ranging from North Carolina down through Florida, the Gulf of Mexico, the Caribbean, and south to Brazil.
Description
A sturdy, nearly symmetrical heart-shaped bivalve featuring prominent, evenly spaced radial ribs that create a deeply corrugated margin. The surface texture is rough to the touch due to tiny, scale-like nodes along the ribs. The hinge is strong, and the overall form is robust, designed to withstand turbulent surf environments.
Key Features
Rounded, heart-shaped profile when viewed from the side, numerous prominent radial ribs (usually around 30 to 35), and fine serrations along the ventral margin where the valves meet.
Collector Value
Low to moderate commercial value, but highly valued by casual beachcombers and regional shell collectors as a representative specimen of Gulf Coast fauna. Typically worth a nominal amount.
Condition Notes
Good condition. The single valve is mostly intact with minor wear along the edges, retaining its structural integrity and distinct ribbing. Graded as Good to Fine collectibility.
Interesting Facts
Cockles are capable of active movement using a muscular, sickle-shaped foot. Instead of slowly crawling like snails, they can use this foot to leap or 'kick' themselves away from predators like starfish.
Ecological Role
Serves as an important prey item for carnivorous snails, crabs, and shorebirds. As filter feeders, they help clarify coastal waters by consuming suspended phytoplankton and organic particles.
Similar Species
Prickly Cockle (Trachycardium egmontianum), which has much sharper, more pronounced spine-like scales along the ribs compared to the smoother, blunter nodes of T. muricatum.
Beach Finding Tips
Look along high tide wrack lines or sift through wet sand after storm events or strong onshore winds, particularly on Gulf Coast beaches like Surfside, Texas.
Notes
Surfside beach Texas