Blake, Daniel B. Department of Geology, University of Illinois, Urbana, Illinois.
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A Paleozoic (Ordovician–Devonian) order of the class Ophiuroidea, consisting of fossil brittle stars. Stenurida (stenurids) have a double row of plates (ambulacra) that abut across the arm axis either directly opposite one another or slightly offset. In contrast, modern ophiuroids have a single series of axial arm plates that are termed vertebrae. In stenurids, as in modern ophiuroids, lateral plates are present at the sides of ambulacrals (see illustration), and prominent lateral spines are typical. Stenurids lack the dorsal and ventral arm shields that are found in most ophiuroids. Proximal ambulacral pairs can be partially separated, forming a buccal slit, an expansion of the mouth frame. The arms of some stenurids are slender and flexible, but those of others are broad and comparatively stiff. The central disk varies from little larger than the juncture of the arms to an expansion that extends most of the length of the arms. The content of the order is poorly established and fewer than 10 genera are known.
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