Studies on western Atlantic Octocorallia (Gorgonacea: Ellisellidae).: Part 7:: The genera Riisea Duchassaing & Michelotti, 1860 and Nicella Gray, 1870

The eleven western Atlantic species belonging to the two ellisellid genera Riisea and Nicella are described and illustrated. Six new species of Nicella are described, and another distinguished as new but not described. A dichotomous key and a table of comparisons is provided for the eleven western Atlantic species of Nicella. An annotated list of the 19 species of this genus is given. Detailed morphology of the double head sclerites and the type of body wall sclerite were used to distinguish species. Specimens of these genera were common at shelf and upper slope depths throughout the tropical western Atlantic, the deepest record being at 819 m. Specimens from 140 stations were examined as well as the types of all previously described species of western Atlantic Nicella.