Important attributes of some taxonomic diversity gradients of marine organisms include an “ocean effect” and a “margin effect.” As examples of the former, both ectoprocts and bivalves are twice as diverse in the Pacific Ocean as in the Atlantic Ocean. As examples of the latter, bivalves and, less clearly, ectoprocts have their greatest within-ocean diversity along the western margin of the Pacific and the eastern margin of the Atlantic Ocean. Correct determination of the paleo-equator may be severely hampered unless the data include samples from the Pacific Basin. Although ectoprocts and bivalves are equally diverse at low latitudes, ectoprocts have markedly more species per geographic area at high latitudes.

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