Information on killer whale systematics and ecology is currently interpreted within the conceptual framework of a single, intermixing species. However, recent evidence suggests that three distinct forms of killer whales (Orcinus sp.) occur in Antarctica during the austral summer. These forms have different prey and habitat preferences, different average school sizes and geographic distributions, and distinct morphologies, and therefore it was suggested that they are best regarded as separate species. All three forms occur in the Ross Sea and the investigators propose to evaluate the separate species hypothesis. If, in fact, there are three distinct species in Antarctic waters, results of the proposed work have the potential to largely re-shape our understanding of killer whale ecology and conservation status in Antarctica. Given their large numbers (current estimates: 25,000-94,000) and status as top trophic level predators, killer whales are undoubtedly key species in the Antarctic ecosystem but their roles will not be understood until their taxonomic status is clarified. Also, the conservation status of killer whales, including potential effects of commercial fishing, depends on properly identifying their taxonomic status, specifying dietary needs, and assessing the impacts of fisheries. Two main goals are proposed: (1) to compare genetic divergence among the three forms and (2) to accurately determine lengths and body proportions for morphological comparisons. The killer whale is arguably one of the most recognizable, and best-studied, large animals on earth, yet basic questions about how many species there are and how they function within the ecosystem remain unanswered. Confirming new species in Antarctic waters would highlight the fact that our knowledge of marine biodiversity is perhaps even more rudimentary than currently recognized.