The spiny river snail, scientific name Io fluvialis, is a species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of 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....

, an aquatic mollusk in the family Pleuroceridae

Pleuroceridae

Pleuroceridae, common name pleurocerids, is a family of small to medium-sized freshwater snails, aquatic gilled gastropod mollusks in the superfamily Cerithioidea.These snails have an operculum and typically a robust high-spired shell....

. It is the only species in the genus Io.

This species is endemic to the Tennessee River

Tennessee River

The Tennessee River is the largest tributary of the Ohio River. It is approximately 652 miles long and is located in the southeastern United States in the Tennessee Valley. The river was once popularly known as the Cherokee River, among other names...

and its larger tributaries, but has been largely extirpated due to pollution and the construction of dams. They live in rapidly flowing well oxygenated waters of shoals and riffles of rivers, but not in slack water below shoals. Preferred water depth is up to 1.5 m., where they feed on the algal coating on rocks. Females lay between 20-100 eggs, which begin to hatch after 15 days.

The shell morphology is variable, with some individuals totally lacking spines. For this reason it was formerly thought that many species existed.