The triangular kidneyshell (''Ptychobranchus greenii'') is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

freshwater mussel Freshwater bivalves are one kind of freshwater mollusc, along with freshwater snails. They are bivalves that live in fresh water as opposed to salt water, which is the main habitat type for bivalves. The majority of species of bivalve molluscs ...

, in the family

Unionidae The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is at its most diverse ...

, the river mussels. It is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

Alabama (We dare defend our rights) , anthem = "Alabama (state song), Alabama" , image_map = Alabama in United States.svg , seat = Montgomery, Alabama, Montgomery , LargestCity = Huntsville, Alabama, Huntsville , LargestCounty = Baldwin County, Al ...

in the United States, where it is known from several rivers and streams in the Mobile River Basin.''Ptychobranchus greenii''.
The Nature Conservancy. It is a federally listed

endangered species An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...

of the United States. This aquatic

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

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 ...

is somewhat oval in shape and may reach 10 centimeters in length. It is yellow to yellow-brown in color. The shell is quite variable in appearance.USFWS
Endangered status for eight freshwater mussels and threatened status for three freshwater mussels in the Mobile River drainage.
''Federal Register'' March 17, 1993. When this mussel breeds it releases its

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e, termed

glochidia The glochidium (plural glochidia) is a microscopic larval stage of some freshwater mussels, aquatic bivalve mollusks in the families Unionidae and Margaritiferidae, the river mussels and European freshwater pearl mussels. These larvae are ...

, glued together in packets called conglutinates. The conglutinate has a sticky filament that adheres to the substrate to prevent it from being washed away. The conglutinate resembles a fly larva,Hartfield, P. and E. Hartfield. (1996)
Observations on the conglutinates of ''Ptychobranchus greeni'' (Conrad, 1834) (Mollusca: Bivalvia: Unionoidea).
''American Midland Naturalist'' 135(2) 370-75. or perhaps a fish egg,USFWS
11 Southeastern Mussels 5-year Review.
April 7, 2008. and it is appetizing to fish. Fish hosts such as the warrior darter (''Etheostoma bellator''), Tuskaloosa darter (''Etheostoma douglasi''), and blackbanded darter (''Percina nigrofasciata'') consume the conglutinates, degrading them and releasing the glochidia, which then lodge in the fish's gills as

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

s. They develop into juvenile mussels and drop out of the fish to develop further elsewhere. Many other mussels in family Unionidae have a similar process. This mussel was known from the

Black Warrior River The Black Warrior River is a waterway in west-central Alabama in the southeastern United States. The river rises in the extreme southern edges of the Appalachian Highlands and flows 178 miles (286 km) to the Tombigbee River, of which the Bl ...

and

tributaries A tributary, or affluent, is a stream or river that flows into a larger stream or main stem (or parent) river or a lake. A tributary does not flow directly into a sea or ocean. Tributaries and the main stem river drain the surrounding drainage b ...

, the

Coosa River The Coosa River is a tributary of the Alabama River in the U.S. states of Alabama and Georgia. The river is about long.U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed April 27, 2011 ...

and its tributaries, and the

Cahaba River The Cahaba River is the longest substantially free-flowing river in Alabama and is among the most scenic and biologically diverse rivers in the United States. It is a major tributary of the Alabama River and part of the larger Mobile River basin. ...

. When it was placed on the Endangered Species List in 1993 it was limited to some tributaries of the Black Warrior River and the

Conasauga River The Conasauga River is a river that runs through southeast Tennessee and northwest Georgia. The Conasauga River is longU.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map, accessed April 27, 2011 an ...

in the Coosa River drainage. Any remaining specimens in the Cahaba River are now treated as members of another species, ''Ptychobranchus foremanianus''. It is extirpated from the main Black Warrior River, but it is present in at least two tributaries, which are protected within

Bankhead National Forest The William B. Bankhead National Forest is one of Alabama's four National Forests, covering . It is home to Alabama's only National Wild and Scenic River, the Sipsey Fork. It is located in northwestern Alabama, around the town of Double Sprin ...

References

Ptychobranchus Molluscs of the United States Endemic fauna of Alabama Bivalves described in 1834 ESA endangered species Taxonomy articles created by Polbot {{Bivalve-stub