|Spondylidae, the thorny oysters, have circular or ovate shaped shells. The left upper shell has irregular shaped and sized spines. The right valve cements to hard substrates and is flatter than the left valve. The hinges of the shells have interlocking balls and sockets to keep the shells aligned. The thorny oysters are closely related to the scallops, but as in to the "true oysters", their shells are cemented to hard substrates instead of attaching by byssal threads. The mantle of the animal has many sensory tentacles with multiple "eyes" around the shell edges. Many species are very colorful. There are 2 species found in Texas waters.