The ideal hydrodynamic form of the concavo-convex productide brachiopod shell

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Abstract

Shiino, Y & Suzuki, Y. 2011: The ideal hydrodynamic form of the concavo-convex productide brachiopod shell. Lethaia, Vol. 44, pp. 329–343.

Water-flume experiments were performed to determine whether the concavo-convex Permian brachiopod Waagenoconcha imperfecta was hydrodynamically adapted for feeding. The generation of passive currents inside the valves was observed experimentally. The use of four transparent, hollow polyhedron models, each differing in a single morphological feature, permitted observation of the currents inside the valves and allowed evaluation of the hydrodynamic significance of the ears and the prominent geniculated trail. Regardless of the direction of ambient flow, only the approximate-imitation model generated a stable flow pattern consisting of inhalation from the ear gapes and exhalation from the anterior trail gape; models lacking or with small changes in these morphological features failed to generate stable flow patterns. The stable flow pattern was probably maintained by a pressure difference between the posterior lower ear gapes (maximum pressure) and the anterior trail gape (minimum pressure). Notably, bilaterally rotating internal currents formed parallel to the brachial ridges; such flow patterns would facilitate the capture of food particles by the animal via tentacles on its lophophore, which is most likely were located on the brachial ridges. Our results demonstrate that the immobile brachiopod W. imperfecta, an animal incapable of widely opening its valves, probably fed on the passive internal currents generated by its shell form. This unique valve morphology appears to be perfectly adapted from a hydrodynamic point of view. □Biomechanics, ecomorphology, evolution, morphological disparity, Productidina, suspension feeder.

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