ABSTRACT
The past two decades have seen numerous discoveries of single-celled parasites (protozoa) infecting marine mammals, including normal biota, primary pathogens, and species that can be categorized as either, depending upon host health status. With the advent of molecular sequencing, several uncharacterized species have been glimpsed from time to time, but their taxonomic identity, biology, and life cycle are unknown, and new marine mammal parasites are continually being discovered. Protozoa infect marine mammals worldwide; several medically important species can cross ecological barriers between terrestrial and marine ecosystems, while others appear to cycle exclusively within the marine environment.
