Cyclostome bryozoans are present in 83 samples collected as part of the Panama Paleontology Project (PPP) and representing sediments deposited during the Miocene-Pleistocene in several basins on the Caribbean and Pacific sides of the Central American Isthmus. Preliminary study has resulted in the identification of 23 species. Most of these are left in open nomenclature and assigned questionably to genera, pending detailed study and comparison with cyclostomes previously described from this region and elsewhere. Maximum sample diversity is 13 species and median diversity two species. An equal number of species is present in the Caribbean and Pacific basins. The cumulative collection curve for the PPP cyclostome samples shows a flattening, implying that further sampling will not increase diversity substantially. About 11 percent of calcareous species in the PPP bryozoan fauna are cyclostomes, the remainder being cheilostomes. This relatively small value is consistent with anecdotal data for Recent bryozoans which suggest a decrease in the proportion of cyclostomes within bryozoan faunas from high to low latitudes. Species with erect colonies dominate among the cyclostomes, in contrast with the PPP cheilostomes in which encrusting species greatly outnumber erect species.

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