"Primnoidae consists of 36 genera, 7 subgenera, and 233 valid species, making it the fourth largest octocorallian family. Species occur in all ocean basins, especially the Antarctic, at depths of 8-5850 m, making primnoids the deepest-living gorgonacean octocorals. Primnoids are common and characteristic of seamounts and deepwater coral banks, often providing habitat for other marine life and serving as proxies for isotopic analyses to determine paleotemperatures. Diagnoses of the primnoid genera and subgenera are based primarily on their type species, and specimens are illustrated by means of scanning electron microscopy, often using stereo images to allow better appreciation of the topology and interconnection of the calycular sclerites. A history of the higher classification of the family is given. Each genus is briefly discussed, and also included are a synonymy of pertinent references, a summary of the geographic and bathymetric ranges, and the deposition of the type specimens of the type species. Four new genera, two new subgenera, one new species, and seven new combinations are proposed. A list of the 233 valid species and the 14 infraspecific taxa is provided along with the purported junior synonyms. An indented dichotomous key is provided for identification of the genera and subgenera. Phylogenetic analysis of the genera and subgenera was performed using 27 morphological characters comprising 94 character states. The cladogram does not consistently support the conventional arrangement of genera into five subfamilies, thus this classification is not followed herein. The origin of the primnoids is inferred to be from an ancestor living in the Antarctic."--Publisher's website. Material and methods -- Results and discussion of character evolution and the evolutionary tree -- Systematic accounts.