Atlantic Thorny Oyster, Spondylus americanus

The Atlantic thorny oyster, Spondylus americanus, is a species of bivalve mollusk within the family Limidae. It can be seen along the Atlantic coast of North America, ranging from North Carolina to Brazil.

This oyster can grow to 3.9 inches in diameter. The valves of its shell are roughly circular and the upper valve is decorated with many spiny protuberances up to 2 inches long. When growing in a crevice, the shell shape adapts itself to the available space. The coloration varies but is normally white or cream with orange or purplish areas making it well camouflaged. The lower valve is flat and attached to the substrate. When the living animal is lying on the seabed, it is normally not visible due to the algae, marine animals and sediment that cover the shell. A diver swimming past may just observe a slight movement on the seabed as the oyster snaps shut. Young animals are much less spiny than the adults and resemble members of the genus Chama.

This oyster can be found in the western Atlantic Ocean, the Caribbean Sea and Gulf of Mexico where it is seen at depths between 30 and 148 feet. Its range extends from North Carolina and Texas southwards to Venezuela and Brazil. It occurs on deep water reefs especially in areas with a high sedimentation level. It’s often lodged in a crevice or concealed under an overhang. It’s also a member of the fouling community, being found on the sea walls, mane made structures and wrecks.

Being a filter feeder, it sifts out plankton and other organic material from the water that passes over its gills. Little is known about its breeding habits but the larvae are plank tonic, seeking out suitable locations on which to settle. Areas with suitable calcareous matter for building the shell are more favorable. The adults are sedentary and usually occupy the same position for the rest of their lives unless shifted by a storm.

Image Caption: Spondylidae: Spondylus americanus Hermann, 1791. Credit: Shellnut/Wikipedia (CC BY-SA 3.0)