The periostracum is a thin organic coating or "skin" which is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among molluscs it is primarily seen in snails and clams, i.e. in gastropods and bivalves, but it is also found in cephalopods such as Allonautilus scrobiculatus. Periostracum is an integral part of the shell, and it forms as the shell forms, along with the other shell layers.
The Chinese mystery snail, black snail, or trapdoor snail, is a large freshwater snail with gills and an operculum, an aquatic gastropod mollusk in the family Viviparidae. The Japanese variety of this species is black and usually a dark green, moss-like alga covers the shell.
Coelatura horei is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels.
The Moapa pebblesnail also known as the Muddy Valley turban snail, scientific name Pyrgulopsis avernalis, is a species of small freshwater snail with an operculum, an aquatic gastropod mollusk in the family Hydrobiidae.
The Chupadera springsnail, scientific name Pyrgulopsis chupaderae, is a species of minute freshwater snails with an operculum, aquatic gastropod molluscs or micromolluscs in the family Hydrobiidae.
The Crystal Spring springsnail, scientific name Pyrgulopsis crystalis, is a species of small freshwater snail, an aquatic gastropod mollusk in the family Hydrobiidae.
The Davis County springsnail, scientific name Pyrgulopsis davisi, is a species of small freshwater snails with a gill and an operculum, aquatic gastropod mollusk in the family Hydrobiidae.
The Ash Meadows pebblesnail is a species of freshwater snail with a gill and an operculum, aquatic gastropod mollusk in the family Hydrobiidae.
The Gila springsnail, scientific name Pyrgulopsis gilae, is a species of freshwater snail with an operculum, an aquatic gastropod mollusk in the family Hydrobiidae.
The Jackson lake springsnail, scientific name Pyrgulopsis robusta, is a species of very small or minute freshwater snail with an operculum, an aquatic gastropod mollusk in the family Hydrobiidae. This species is endemic to the United States. The shell is 4.6 to 7.5 millimetres high and 1.48 to 2.10 millimetres wide, which is large for this genus. It has 4.5 to 6.25 whorls, and is clear-white with a tan periostracum.
Reymondia horei is a species of freshwater snail with an operculum, an aquatic gastropod mollusk in the family Paludomidae. This species is found in Burundi, the Democratic Republic of the Congo, Tanzania, and Zambia. Its natural habitat is freshwater lakes.
Reymondia minor is a species of small freshwater snail, an aquatic gastropod mollusc in the family Paludomidae. This species is found in Burundi, the Democratic Republic of the Congo, Tanzania, and Zambia. Its natural habitat is freshwater lakes.
Stanleya neritinoides is a species of freshwater snail, an aquatic gastropod mollusk in the family Paludomidae.
Tanganyicia rufofilosa is a species of tropical freshwater snail with an operculum, an aquatic gastropod mollusk in the family Paludomidae.
Tiphobia horei is a species of freshwater snail with an operculum, an aquatic gastropod mollusk in the family Paludomidae.
Freshwater snails are gastropod mollusks which 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.
Tylomelania gemmifera is a species of freshwater snail with an operculum, an aquatic gastropod mollusk in the family Pachychilidae.
Pyrgulopsis aardahli, commonly known as the Benton Valley springsnail, is a species of minute freshwater snails with an operculum, aquatic gastropod molluscs or micromolluscs in the family Hydrobiidae.
Pyrgulopsis archimedis, commonly known as the archimedes pyrg, is a species of minute freshwater snails with an operculum, aquatic gastropod molluscs or micromolluscs in the family Hydrobiidae.
Pyrgulopsis arizonae, commonly known as the Apache springsnail, is a species of minute freshwater snails with an operculum, aquatic gastropod molluscs or micromolluscs in the family Hydrobiidae.
