Reuscher, Michael Gerhard2024-06-272024-06-272013-11-15https://hdl.handle.net/1969.6/98086A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Marine Biology.Polychaetes are abundant and ecologically important benthic organisms, yet their diversity and phylogenetic relationships are far from being resolved. The purpose of my dissertation was to measure their diversity in the Gulf of Mexico and to compare polychaete assemblages of different regions, depths, and sampling periods. Furthermore, I studied the natural history of the diverse polychaete family Paraonidae. The polychaete diversity of the Gulf of Mexico was examined using a comprehensive species database. Species were assigned to ecological, morphological, and biogeographical categories and each category's contribution was examined throughout different depths and regions. Spatial and temporal comparisons of polychaete assemblages were conducted at three transects on the northern Gulf of Mexico continental slope. Phylogenetic relationships within the family Paraonidae were studied based on the examination of type material. Polychaete diversity changed with depth. The shelf break was accompanied by a steep change in the species composition. The southeastern Gulf had the most distinct polychaete fauna. Endemism was at 10%; in the deep-sea more than 30% of the species were endemic and the relative contribution of carnivorous species doubled. At the continental slope, abundance did not continuously decrease with depth between 350 and 1500 m, but dropped between 1500 and 2100 m. Abundance in the spring was approximately twice as high as in the fall, in depths up to 1500 m. Polychaete assemblages changed continuously with increasing depth. Short-term temporal changes of polychaete assemblages had reversed in the long run. In the cladistic analyses, monophyly of Paraonidae was supported. Its synapomorphies are the complete fusion of prostomium and peristomium and the dorsal location of the anus. Cirrophorus and Paradoneis should be considered synonyms. The prostomial antenna, which was used to distinguish both genera, is a homoplastic character. Two species of Paradoneis are being moved to a new genus. Spatial and temporal patterns of polychaete diversity in the Gulf of Mexico were discovered. Additional sampling efforts are needed for a more complete picture of the diverse polychaete fauna. The phylogenetic analyses based on morphology resolved important issues. However, additional genetic markers are needed to uncover sister species relationships.en-USbiodiversitycommunity ecologyGulf of MexicoparaonidaephylogenypolychaetaThesis