The biodiversity of marine heterotrophic protists is poorly known in the South Atlantic coastal zone (~32 °S) especially regarding the nanoflagellates. The presence of loricate choanoflagellates was reported for the first time in the Patos Lagoon estuary and the adjacent coastal zone. Seventeen species of eleven genera of loricate choanoflagellates were observed between October 1998 and May 2000 in fixed water samples (lugol's solution + glutaraldehyde) in a JEM 100-SX transmission electron microscope. Most species were recorded in euhaline and mixopolyhaline waters during the spring and summer, none in autumn and a few (four) in winter. The absence of choanoflagellates at the more sheltered inshore stations is due freshwater influence, and at the beach station, probably due the strong wave action. The probably cosmopolitan species Pleurasiga minima, Cosmoeca norvegica, C. ventricosa and Parvicorbicula circularis were present in spring or summer in the estuary channel and coastal area while Stephanoeca diplocostata which apparently prefers lower temperature, was recorded in winter. Calotheca alata and Campyloacantha spinifera are mainly temperate species and were present in spring. The new species Diplotheca tricyclica was recorded at the estuary channel in the summer 1999, in high salinity water.
nanoflagellates; taxonomy; heterotrophic protists; south Brazil
