Planorbidae, common name the ramshorn snails or ram's horn snails, is a family of air-breathing freshwater snails, aquatic pulmonate gastropod molluscs. Unlike most molluscs, the blood of ram's horn snails contains iron-based hemoglobin instead of copper-based hemocyanin. As a result, planorbids are able to breathe oxygen more efficiently than other molluscs. The presence of hemoglobin gives the body a reddish colour. This is especially apparent in albino animals.
Planorbidae
Albino planorbid clearly shows the reddish-colored body tissues due to the pigment hemoglobin
View of the sunken spire of the shell of Anisus septemgyratus
Planorbarius corneus. View of the sunken spire (held facing downwards in life)
Freshwater snails are gastropod mollusks that live in fresh water. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and springs to major rivers. The great majority of freshwater gastropods have a shell, with very few exceptions. Some groups of snails that live in freshwater respire using gills, whereas other groups need to reach the surface to breathe air. In addition, some are amphibious and have both gills and a lung. Most feed on algae, but many are detritivores and some are filter feeders.
Bithynia tentaculata, a small freshwater gastropod in the family Bithyniidae
Pomacea insularum, an apple snail
Planorbella trivolvis, an air-breathing ramshorn snail
Family Neritidae, Neritina natalensis