How do lamp shells open and close their shells?

The mechanism for opening and closing the shells of lamp shells (brachiopods) depends on their classification:

• Articulate Brachiopods: These possess a hinge with teeth and sockets. They open their shells by contracting diductor muscles, which extend from the ventral valve to a process under the dorsal beak. This action pulls the dorsal beak forward, rotating it on the hinge. To close the valves, the animal contracts its adductor muscles.1
• Inarticulate Brachiopods: These lack a hinged mechanism. Instead, their valves are held together by a complex set of muscles that both open the valves and slide them laterally to facilitate feeding.1

It is important to note that while lamp shells may superficially resemble bivalve mollusks, they are biologically distinct, and their internal anatomy and muscle functions differ significantly from those of bivalves.12