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an extinct order of invertebrates of the class Tes-ticardines of the phylum Brachiopoda. Spiriferida existed from the Ordovician to the Middle Jurassic. The shell had convex ventral and dorsal valves and was elongated mainly laterally, with well-developed areas along the posterior margin, or hinge line. The skeleton supported arms and consisted of two conical spiralia whose apexes were directed laterally. Spiriferida were benthic organisms, which attached themselves to a substrate by means of outgrowths, or stalks, that emerged through a special opening in the shell. Spiriferida are valuable in determining the stratigraphy of Paleozoic deposits.