Thecideida

Thecideida is an order of cryptic articulate brachiopods characterized by their small size and habit of cementing their ventral valves to hard substrates such as shells, rocks and carbonate hardgrounds. Thecideides first appeared in the Triassic and are common today.

Taxonomy
Order Thecideida
 * Superfamily Thecideoidea Gray, 1840
 * Superfamily Thecospiroidea Bittner, 1890