Preliminary systematics and diversity patterns of cyclostome bryozoans from the neogene of the Central American Isthmus

Cyclostome bryozoans are present in 83 samples collected as part of the Pan ama Paleontology Project (PPP) and representing sediments deposited during the Miocene-Pleistocene in several basins on the Caribbean and Pacific side s of the Central American Isthmus. Preliminary study has resulted in the id entification of 23 species. Most of these are left in open nomenclature and assigned questionably to genera, pending detailed study and comparison wit h cyclostomes previously described from this region and elsewhere. Maximum sample diversity is 13 species and median diversity two species. An equal n umber of species is present in the Caribbean and Pacific basins. The cumula tive collection curve for the PPP cyclostome samples shows a flattening, im plying that further sampling will not increase diversity substantially. Abo ut 11 percent of calcareous species in the PPP bryozoan fauna are cyclostom es, the remainder being cheilostomes. This relatively small value is consis tent with anecdotal data for Recent bryozoans which suggest a decrease in t he proportion of cyclostomes within bryozoan faunas from high to low latitu des. Species with erect colonies dominate among the cyclostomes, in contras t with the PPP cheilostomes in which encrusting species greatly outnumber e rect species.