Planorbidae

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. Being air breathers like other Panpulmonata, planorbids do not have gills, but instead have a lung. The foot and head of planorbids are rather small, while their thread-like tentacles are relatively long. Many of the species in this family have coiled shells that are planispiral, in other words, the shells are more or less coiled flat, rather than having an elevated spire as is the case in most gastropod shells. Although they carry their shell in a way that makes it appear to be dextral, the shell of coiled planorbids is in fact sinistral in coiling, but is carried upside down, which makes it appear to be dextral. For several taxa, no consensus exists as to whether the taxa should even be assigned to the family Planorbidae. This is certainly the case with the freshwater limpets Ferrissia, and Ancylus. Both of these genera have sometimes been assigned to the family Lymnaeidae. Alternatively sometimes each one of them is raised to the level of a family. However, according to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005), these genera are currently placed in the tribe Ancylini within the family Planorbidae, and that is the taxonomic system that is followed here. According to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005), this family consists of the following subfamilies: Albrecht et al. (2007) analyzed a limited number of genera of Planorbidae, based on sequences of mitochondrial 18S ribosomal DNA and cytochrome-c oxidase I (COI) genes, and on the basis of the results, they rearranged the taxonomy like this: 'A-clade' sensu Albrecht et al. (2007) Tribus Bulinini