The arm system of Barycrinus asteriscus is reconstructed to interpret the feeding dynamics of this Early Mississippian crinoid. As a cyathocrine inadunate, B. asteriscus had ramulate arm branching and possessed a multi-layered, bilaterally symmetrical filtration fan with a 46% overlap of arms. Study of the steromic microstructure of radial facets indicates that different arms had differing mobilities. The very complex filtration fan of this crinoid is inferred to have been an adaptation allowing it to occupy a position in niche space between normal ramulate and pinnulate crinoids. The multi-layering and arm overlap was an adaptation to enhance feeding efficiency, and the bilateral symmetry of the filtration fan may have increased stability for individuals in a feeding position. A new, large type of stereom pores housed tissue responsible for arm stability.--Journal abstract.

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