Mysida

Mysida, commonly known as mysids or opossum shrimps, is an order of small, shrimp-like crustaceans in the class Malacostraca. They occur in a wide range of aquatic environments, including marine, brackish, and some freshwater systems, from coastal shelves to lakes and rivers. They are typically a few millimeters to a few centimeters long and are often pale and translucent, with a slender body adapted for swimming in the water column. A key feature is the marsupium in females, a brood pouch under the thorax where eggs and early juveniles develop.

Reproduction and development proceed with females brooding eggs in the marsupium until hatching. The released juveniles resemble adults and grow through molts, passing through several instars before reaching maturity. Mating systems are generally dioecious, with separate sexes, though specific behaviors vary among species.

Ecology and role in ecosystems: Mysids are omnivorous, feeding on phytoplankton, microzooplankton, detritus, and occasionally small crustaceans. They are an important intermediate consumer in aquatic food webs, transferring energy from primary production to larger predators such as fish, seabirds, and invertebrates. Many species undertake diel vertical migration, residing in deeper waters by day and moving to upper layers at night to feed.

Taxonomy and human relevance: The order Mysida comprises several families of mysid crustaceans. They are studied for ecological and toxicological purposes and are widely used as a high-quality live food in aquaculture and aquarium settings due to their nutritional value and ease of culture.