''Hebetancylus excentricus'', the excentric ancylid, is a species of small,

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

, air-breathing

limpet Limpets are a group of aquatic snails that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" descended indep ...

, an aquatic

pulmonate Pulmonata or pulmonates, is an informal group (previously an order, and before that a subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group includ ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

micromollusc A micromollusk is a shelled mollusk which is extremely small, even at full adult size. The word is usually, but not exclusively, applied to marine mollusks, although in addition, numerous species of land snails and freshwater mollusks also r ...

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

Geographic distribution

''H. excentricus'' is widely distributed across North and Central America and the

Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...

. The main area of its North American range extends from Florida to Texas, but it has also been reported from scattered ponds and river backwaters along the length of the southern Atlantic Coastal Plain as far north as North Carolina. This pattern of contagious distribution suggests that the species is possibly being dispersed through the air by migratory waterfowl.

Habitat and ecology

''H. excentricus'' usually occurs on rocks in fast-flowing streams and occasionally on rocks and rooted aquatic vegetation in lakes and the impounded backwaters of rivers and streams. It also occurs on submerged sticks, logs, and large items of organic debris. Annual,

bi- Numeral or number prefixes are prefixes derived from numerals or occasionally other numbers. In English and many other languages, they are used to coin numerous series of words. For example: * unicycle, bicycle, tricycle (1-cycle, 2-cycle, 3-cy ...

and trivoltine life cycles have been reported in Louisiana and Texas populations of ''H. excentricus''; however, this increased number of generations occurs without an increase in population growth rates.

References

Planorbidae Molluscs of North America Gastropods described in 1851 {{planorbidae-stub