Invertebrates
Mysid
Mysida · also called opossum shrimp
Nearly invisible in open water, a swarm of mysids drifts past, each female carrying her own developing young in a pouch beneath her body, a small crustacean quietly filling the gap between plankton and the fish that depend on it.
Overview
The mysid, order Mysida, is a small, often translucent crustacean found across marine and freshwater habitat worldwide. Its marsupial-like brood pouch and foundational role linking plankton to larger predators make it one of the more ecologically important yet visually overlooked animals in aquatic food webs.
A tiny crustacean holding up a much bigger food web
Rarely noticed and easily mistaken for true shrimp, the mysid nonetheless plays an outsized ecological role, its sheer abundance quietly supporting fish populations that depend on it far more than most people ever realise.
Status
Not Evaluated — abundant across suitable marine and freshwater habitat worldwide, playing a largely secure ecological role.
Mysid: common questions
Why is the mysid called an opossum shrimp?
A female mysid carries developing young in a brood pouch called a marsupium, located beneath the thorax, a reproductive strategy directly comparable to how a marsupial such as an opossum carries its own young, a resemblance striking enough that it gave the entire mysid group its common nickname.
Is a mysid actually related to true shrimp?
No, despite being commonly called opossum shrimp, a mysid is not a true shrimp at all, belonging instead to an entirely separate crustacean order, meaning the resemblance in general body shape is closer to a case of superficial similarity than a genuine close relationship.
Why are mysids so important in aquatic food webs?
Mysids form a critical link in many aquatic food webs, feeding on plankton and detritus while themselves serving as an important food source for fish and other larger predators, meaning their abundance can directly influence the productivity of the fish populations that depend on them.
Do all mysids live in open water?
No, while many mysid species swim in open marine or freshwater habitat, certain species live permanently in caves or deep water environments, with some cave-adapted species having lost functional eyesight entirely, an adaptation to a life spent in permanent darkness.