How do articulate and inarticulate lamp shells differ?

The primary distinction between articulate and inarticulate lamp shells (brachiopods) lies in the mechanism used to connect their two valves.

• Articulate Brachiopods: These possess a specialized hinge mechanism featuring teeth and sockets that lock the valves together. Their shells are always composed of calcium carbonate (calcite). Internally, they have a more specialized anatomy, including a digestive system that lacks an anus, meaning waste is excreted through the mouth.12
• Inarticulate Brachiopods: These lack a hinge with teeth and sockets; instead, their valves are held together solely by a complex system of muscles. Their shells are typically composed of chitinophosphatic material. Unlike their articulate counterparts, inarticulate brachiopods possess an intestine that terminates in an anal opening.12

While both groups utilize a lophophore for filter feeding, their structural differences reflect distinct evolutionary specializations in how they manage their shells and process nutrients.234