55731 is a Postal Code in St. Louis County.
- 55731 a.k.a. Hydrobiidae, common name mud snails, is a large cosmopolitan taxonomic family of very small freshwater snails and brackish water snails that have an operculum, aquatic gastropod mollusks in the clade Littorinimorpha.
- 55731 a.k.a. chromosome 17 open reading frame 63 is a gene.
- also known as hypothetical protein LOC55731