# Physella acuta

Physella acuta is a species of small, left-handed or sinistral, air-breathing freshwater snail, an aquatic gastropod mollusk in the family Physidae. Common names include European physa, tadpole snail, bladder snail, and acute bladder snail.

## Etymology

The name Physella means "little bladder", from Greek physa, and the diminuative ending "-ella". This is in reference to the genus Physa, which P. acuta has, at times, been placed in. Acuta is a Latin word meaning sharp.

## Shell description

Snails in the family Physidae have shells that are sinistral, which means that if the shell is held with the aperture facing the observer and the spire pointing up, then the aperture is on the left-hand side.
The shells of Physella species have a long and large aperture, a pointed spire, and no operculum. The shells are thin and corneous and rather transparent.

## History

It was once thought that the indigenous distribution of Physella acuta is Mediterranean. However, recent genetic analysis has revealed it to be the same species as Physella heterostropha of North America. Researchers now increasingly consider P. acuta to be native to North America, so it may have only later been introduced to Europe.

## Distribution

The freshwater snail Physella acuta is common in all of North America and Europe including the United Kingdom. The species seems to have first spread through the Mediterranean regions and then more slowly into Northern Europe. This species has been introduced into New Zealand and is widespread throughout both islands in ponds, lakes, and running water. Physella acuta is presumed to occur also in Southern Africa. Today, it can be found on all continents besides Antarctica.

## Beneficial Pests

Physella acuta is a relatively common freshwater aquarium pest. It usually spreads by laying its eggs on plants which are then bought and taken home. Physella acuta can be annoying and reproduce quickly compared to other snails. It is generally non-harmful to the aquarium, but often found to be unsightly as well as adding to the aquarium's waste production.

### In the United Kingdom

Within the United Kingdom, P. acuta is considered to be an invasive species. It is prolific and has undergone naturalisation. P. acuta has been observed on several great Rivers, streams and tributaries within England, Wales, Scotland and Northern Ireland including the River Severn and the River Thames. The ecological impact of this invasive species to the native floral and faunal species of the United Kingdom was assessed by the United Kingdom Technical Advisory Group (UKTAG) as "Unknown" under the Water Framework Directive guidelines for Alien species.

### In Europe

This species is found in:
* Belgium
* Serbia (it is especially abundant in the Drina river)
* Croatia
* Italy
* Czech Republic – not evaluated (NE)
* Slovakia
* Germany
* Netherlands
* Pripyat River since 1983 and in Neman River basin in Belarus since 2007
* Denmark
and others
The distribution also includes Mediterranean regions and Africa.

### In the Americas

The distribution includes the United States east of the Rocky Mountains
* Cuba – native, the most common freshwater snail there alongside Tarebia granifera
* Chile – invasive

### In Asia

* India
* Uzbekistan
* Kazakhstan

## Ecology
### Habitat

This species lives in freshwater rivers, streams, lakes, ponds, and swamps.
Physella acuta is frequently found in anthropogenic reservoirs, occurring in warm water discharges from power stations and in some rivers, but very rarely and not numerously in clay pit ponds. It can survive well under temporary harsh conditions (extreme temperature and water pollution), as long as they are short-lived.

### Feeding habits

These snails eat dead plant and animal matter and various other detritus.
Because Physella acuta forages mainly on epiphytic vegetation and on the macrophytes, whereas other gastropods (Planorbis planorbis, Radix ovata) exploit the algal cover or phytobentos on the bottom, competition between Physella acuta and other gastropods appears to be minimal.

## Interspecific relationship

This species successfully co-exists with other alien gastropods: for example with Potamopyrgus antipodarum in many streams, lakes and ponds in both New Zealand and the United Kingdom; and with Lithoglyphus naticoides in the Danube River. The presence of P. acuta may encourage proliferation of invasive non-native macrophytes such as Nuttall's waterweed (Elodea nuttallii)

## Predators

The bladder snail is a frequent prey of many snail-eating predators, such as
* Anomalochromis
* Badis badis
* Carinotetraodon travancoricus
* Puntius titteya
* Ambastaia sidthimunki
* Chromobotia macracanthus
* Clea helena
* Sternotherus carinatus
* Glossiphonia weberi

## Reproduction

P. acuta is a self-compatible hermaphrodite. In natural populations, P. acuta preferentially reproduces by outcrossing. When individuals from such populations self-fertilize they show a high degree of inbreeding depression. However, in experimentally constrained lines (where mates were often unavailable), after about 20 generations of self-fertilization, most of the inbreeding depression was purged.

## In the aquarium

P. acuta is one of a variety of snails often called "pest snails" in freshwater fishkeeping, due to their tendency to be inadvertently introduced into tanks via hitching a ride on ornamental plants, combined with how readily and quickly they reproduce due in part to their ability to self-fertilize. Others will however intentionally keep bladder snails, as their diet and ease of care can prove to make them a useful part of a tank's clean-up crew.