Marine microorganism Marine microorganism Marine microorganisms are defined by their habitat as the microorganisms living in a marine environment, that is, in the saltwater of a sea or ocean or the brackish water of a coastal estuary. A microorganism (or microbe) is any microscopic living organism, that is, any life form too small for the naked human eye to see, needing a microscope. Microorganisms are very diverse. They can be single-celled or multicellular and include all bacteria and archaea and most protozoa, as well as some species of fungi, algae, and certain microscopic animals, such as rotifers. Many macroscopic animals and plants
Freshwater snail of primitive "prosobranch" gilled snails which have a shelly operculum. The Caenogastropoda are a large group of gilled operculate snails, which are largely marine. In freshwater habitats there are ten major families of caenogastropods, as well as several other families of lesser importance: Basommatophorans are pulmonate or air-breathing aquatic snails, characterized by having their eyes located at the base of their tentacles, rather than at the tips, as in the true land snails Stylommatophora. The majority of basommatophorans have shells that are thin, translucent, and relatively colorless, and all five freshwater basommatophoran families lack an operculum. Several different freshwater snail