; subclass Actinopterygii, order Acipenseriformes)
A small family of freshwater fish that have many fossil relatives. They are very elongate, with a long, paddle-shaped snout, probably used for feeding on minute organisms sifted from the water. The skin is naked apart from some ganoid scales near the tail. The American species Polyodon spatula (1.8 m) is found throughout the Mississippi system and is locally of some commercial importance. Its only relative, Psephurus gladius, occurs in the Yangtze river, China.
Subjects: Zoology and Animal Sciences.