The Articulata is a class of brachiopod

Brachiopod

Brachiopods are a phylum of marine animals that have hard "valves" on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection...

s which comprises those with hinged, calcareous shells that generally bear well developed teeth and sockets and a simple muscle system. The name was first applied to this major group of brachiopods by Huxley in 1869, ten years prior to Zittel

Karl Alfred von Zittel

Karl Alfred Ritter von Zittel was a German palaeontologist.-Biography:He was born at Bahlingen in Baden, and educated at Heidelberg, Paris and Vienna. For a short period he served on the Geological Survey of Austria, and as assistant in the mineralogical museum at Vienna...

 choosing the same name in 1879 for modern crinoids.

The Articulata has been replaced by the Subphylum Rhynchonelliformea

Rhynchonelliformea

Rhynchonelliformea is the name now given to the articulate brachiopods, Class Articulata, revised as a subphylum. Articulate brachiopods are those with hard, articulated, shells with a simple set of opening and closing muscles....

which except for taxonomic rank and revision of some taxa within, is essentially synonymous.

Moore, Lalicker, and Fischer, 1952, divided the Articulata into the –

• Paleotremata
• Orthida
• Terebratulida
• Pentamerida
• Rhynconellida
• Strophomenida
• Spiriferida.

The earlier version of the Treatise, part H, 1965, is similar, except for the elimination of the Paleotremata and the order in which the remaining orders are presented.