Introduction: Costa Rica Dome is considered as a place with great importance, characterized by an upwelling event with high primary productivity. Siphonophores are predatory organisms that constitute one of the most abundant groups of the zooplankton biomass. Objective: To analyze the specific composition, abundance and distribution of siphonophores from the upwelling region of the central America. Methods: Samples were obtained during the oceanographic campaign DOMO I, which was carried out during February and March of 1979 by the ‘Laboratorio de Oceanografía Física del Instituto de Ciencias del Mar y Limnología de la Universidad Nacional Autónoma de México (UNAM)’. The zooplankton samples were collected with a standard CalCoFI net with 0.3 mm mesh, and then analyzed in the laboratory. Results: A total of 30 species were identified, of which 27 belong to the suborder Calycophorae and three to the suborder Physonectae. Eudoxoides mitra, Muggiaea atlantica, Chelophyes contorta and Lensia hotspur were dominant species. C. contorta was observed with a wide distribution in the study area occupying 85% of the stations. It is followed by Eudoxoides mitra (82%), Agalma okeni (73%), Muggiaea atlántica (64%) and Abylopsis eschscholtzi (61%). The poligastric stage of calycophores species was predominant and the eudoxie stage was only observed in Diphyes dispar, Eudoxoides mitra, Chelophyes appendiculata, Ceratocymba dentata, Abylopsis eschscholtzi, Abylopsis tetragona, Bassia bassensis and Enneagonum hyalinum. Conclusion: The high diversity and density of siphonophores in this research show their importance on the great productivity in the Costa Rica Dome.

Keywords: siphonophores; composition; diversity; density; distribution; Costa Rica Dome.