Planorbella 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 freshwater air-breathing snail

Snail

Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...

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...

 pulmonate 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

Planorbidae

Planorbidae, common name the ramshorn snails or ram's horn snails, is a family of air-breathing freshwater snails, aquatic pulmonate gastropod mollusks....

, the ram's horn snails, or planorbids, which all have sinistral

Sinistral

Sinistral and dextral are scientific terms that describe chirality or relative direction in a number of disciplines.The terms are derived from the Latin words for “left” and “right” ....

, or left-coiling, shells.

Understanding the shell coiling

Planorbid gastropod shell

Gastropod shell

The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...

s are hard to make sense of in terms of their coiling and orientation. Most of the shells in this family are almost planispiral in coiling, and it is important to bear in mind the fact that all planorbids have sinistral shells. To complicate matters further however:

• In life, these pond snails often tend to hold their shells upside down, with the umbilicus
  Umbilicus (mollusk)
  The umbilicus of a shell is the axially aligned, hollow cone-shaped space within the whorls of a coiled mollusc shell. The term umbilicus is often used in descriptions of gastropod shells, i.e...
  
   facing upward
• The spire of the shell is quite sunken in many species
• The umbilicus of the shell is very wide, and it in some species the umbilicus is not as deeply "dished" as the sunken spire is

The planorbid shell is sinistral, such that one can hold the shell with the aperture on the left and facing the holder; then the sunken spire side of the shell will be uppermost. That is to say: the side of the shell which is in fact the spire (a sunken spire) often is carried facing down in the living animal, contrary to what is the case in almost all other shelled gastropods.

Ecology

Species in the Planorbella genus are sometimes hosts for parasites, constituting a link in the pathway of infection for higher animals. For example, some species of Planorbella host rediae and cercariae stages of the parasite Ribeiroia

Ribeiroia

Ribeiroia is a group of trematode parasites that sequentially infect freshwater snails in the family Planorbidae as first intermediate hosts, fish and larval amphibians as second intermediate hosts, and birds and mammals as definitive hosts...

, prior to ultimate infection of the Rough-skinned Newt

Rough-skinned Newt

The rough-skinned newt is a North American newt known for its strong poison.- Toxicity :Many newts produce toxins to avoid predation, but the toxins of the genus Taricha are particularly potent...

.

Planorbella are often algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 grazers, and in some locations such as oligotroph

Oligotroph

An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments...

ic slough

Slough

Slough is a borough and unitary authority within the ceremonial county of Royal Berkshire, England. The town straddles the A4 Bath Road and the Great Western Main Line, west of central London...

s, they may be a dominant element of total ecosystem biomass and hence system integrity.

Species

Species within the genus Planorbella include:

• Planorbella ammon (Gould, 1855)
• Planorbella binneyi (Tryon, 1867)
• Planorbella campanulata (Say, 1821)
• Planorbella columbiensis (F. C. Baker, 1945)
• Planorbella corpulenta (Say, 1824)
• Planorbella duryi
  Planorbella duryi
  Planorbella duryi, common name the Seminole rams-horn, is a species of air-breathing freshwater snail, a pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails.-Distribution:This species of snail is endemic to Florida, USA....
  
  (Wetherby, 1879)
• Planorbella magnifica (Pilsbry, 1903)
• † Planorbella multivolvis (Case, 1847)
• Planorbella occidentalis (J. G. Cooper, 1870)
• Planorbella oregonensis (Tryon, 1865)
• Planorbella pilsbryi (F. C. Baker, 1926)
• Planorbella scalaris (Jay, 1839)
• Planorbella subcrenata (Carpenter, 1857)
• Planorbella tenuis (Dunker, 1850)
• Planorbella traski (I. Lea, 1856)
• Planorbella trivolvis
  Planorbella trivolvis
  Planorbella trivolvis is a species of freshwater air-breathing snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails, or planorbids, which all have sinistral or left-coiling shells.-Description:...
  
  (Say, 1817)
• Planorbella truncata (M. Miles, 1861)