Rhodacmea is a genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of small freshwater snail

Freshwater snail

A freshwater snail is one kind of freshwater mollusc, the other kind being freshwater clams and mussels, i.e. freshwater bivalves. Specifically a freshwater snail is a gastropod that lives in a watery non-marine habitat. The majority of freshwater gastropods have a shell, with very few exceptions....

s or limpet

Limpet

Limpet is a common name for a number of different kinds of saltwater and freshwater snails ; it is applied to those snails that have a simple shell which is more or less conical in shape, and either is not spirally coiled, or appears not to be coiled in the adult snails.The name limpet is most...

s, aquatic

Aquatic animal

An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...

 gastropod mollusks in the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Planorbidae, the ram's horn snails and their allies.

Rhodacmea is the type genus

Type genus

In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...

 of the subfamily Rhodacmeinae.

Anatomy

These animals have a pallial lung, as do all pulmonate snails, but they also have a false gill or "pseudobranch". This serves as a gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

 as, in their non-tidal habitat these limpets never reach the surface for air.

Species

Species in the genus Rhodacmea include:

• Rhodacmea elatior (Anthony, 1855) - Domed ancylid
  Domed ancylid
  The domed ancylid, scientific name Rhodacmea elatior, is a species of small freshwater snail or limpet, an aquatic gastropod mollusk in the family Planorbidae, the ram's horn snails and their allies....
  
  
• Rhodacmea filosa (Conrad, 1834) - Wicker ancylid
  Wicker ancylid
  The wicker ancylid, Rhodacmea filosa, is a species of small, air-breathing, freshwater snail or limpet, a pulmonate gastropod in the family Planorbidae.Rhodacmea filosa is the type species of the genus Rhodacmea.- Distribution :...
  
  , type species
• Rhodacmea hinkleyi (Walker, 1908)