Conulariids
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Conulariids have been the subject of speculation for a century and a half. They aren't that uncommon; there are a number of genera, and they ranged from the Middle Ordovician to the Triassic. There are even a few cases in which conulariid soft parts have been preserved. Nonetheless, exactly what they were is still not settled. Because of their fourfold symmetry, they have often been placed in the Cnidaria by analogy with the fourfold Scyphozoa. However, their skeleton was very different from anything known in the Cnidaria, and they may represent a separate, extinct phylum, probably triploblastic. Connulariids had elongated, pyramidal exoskeletons, made up of rows of calcium phosphate rods. Most were square or rectangular in cross section, with prominent grooves at the corners. They lived attached to hard objects by a flexible stalk, and often lived in groups. Presumably they were filter feeders; how they reproduced is not known. [1]