The scutellid echinoid M. quinquiesperforata is abundant on most littoral and sublittoral sandy substrates along the southeastern Atlantic and northern Gulf coasts, and is common in Pleistocene deposits of those areas. Its feeding and burrowing activities substantially modify the substrate and thus have considerable paleoecological and sedimentological significance. Field and laboratory studies at Beaufort, N.C., have revealed that during feeding the sand dollar size-sorts the detrital grains, ingesting the finer sand particles, then passing these upward through the posterior lunule, and moving the coarser grains to the borders of its trail. In burrowing, the echinoid tends to glide between sediment layers, but the fabric of the overlying sand is disrupted by vertical displacement and collapse; in more viscous substrates, the upper layer is disrupted horizontally as well.

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