The Opossum shrimp (Neomysis americana) is regarded as the premier shrimp in the Chesapeake Bay. It is not however a true shrimp (these belong to the order Decapoda) but a member of the order Mysidacea, often called mysid shrimps.

Neomysis americana is classified in the family Mysidae. This shrimp is tiny, averaging 1.5 to 3 cm. in length with exceptional specimens growing to 3.5 cm. in length. The opossum shrimp is a brilliant red and self-luminescent. Freshwater crustaceans may become luminous when infected with luminous bacteria. The opossum shrimp does not have gills; its split feet serve as its means of respiration and locomotion.

The opossom shrimp gets its name from the brood pouch formed by plates on the thoracic feet for the female; opossums also carry their young in a pouch, being marsupials. The eggs are hatched in the pouch and the young are cared for until their appendages are fully grown. If conditions are favorable these shrimp spawn every 10-14 days. They have a life expectancy of 6-8 months. The opossum shrimp eat a variety of zooplankton, especially copepods and Cladocera. The shrimp's split feet also create a current in the water in which food gets caught and brought within the grasp of its mouth. The opossum shrimp has no natural defenses. Among its predators are the white perch, bluefish and sand flounder.

The opossum shrimp is of enormous economic value to the bay. These shrimp keep the bay thriving by serving as food for other animals in the bay, which are then fished for profit. They also are ground up by humans into a paste used for fish bait. This is a relatively profitable industry.