Greeniedeets buccaneer n. gen., n. sp. (Hyponeoidae, Siphonostomatoida, Copepoda) infects the olfactory sac of a gulper shark, Centrophorus sp. (Centrophoridae, Squaliformes) off Madagascar. The adult female of Greeniedeets buccaneer n. gen., n. sp. is most easily distinguished from other hyponeoids (Hyponeoidae) by its possession of a genital complex that is horseshoe shaped in dorsal view. An amended family diagnosis for Hyponeoidae and diagnostic key to hyponeoids based on adult females are provided.