What term describes a species that lives in freshwater environments?

The term that describes a species living in freshwater environments is "limnic." This term specifically refers to organisms that inhabit freshwater habitats, such as rivers, lakes, and ponds. Limnic environments are characterized by their low salinity levels compared to marine environments, which have a higher salt concentration.

By utilizing the term "limnic," one can accurately communicate the ecological niche of species that are adapted to freshwater systems. This adaptation may include physiological traits that enable survival and reproduction in freshwater conditions, such as osmoregulation to maintain fluid balance.

The other options refer to different types of environments: "marine" indicates species adapted to saltwater conditions, "pleistocene" designates a geological epoch, and "estuarine" refers to species that inhabit areas where freshwater meets saltwater, such as in estuaries. Each of these terms is relevant in its own context but does not apply specifically to freshwater environments like "limnic" does.