Praunus flexuosus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Mysida
Family:	Mysidae
Genus:	Praunus
Species:	P. flexuosus
Binomial name
Praunus flexuosus (O. F. Müller, 1776)

Praunus flexuosus, known as the chameleon shrimp, is a species of opossum shrimp found in European waters. It reaches 26 mm (1.0 in) long, with a distinctly bent body, and closely resembles Praunus neglectus. It lives in shallow water and tolerates a wide range of salinities. It is found from northern France to the Baltic Sea, and was introduced to North America in the mid 20th century.

Praunus flexuosus is a long, slender animal, with a pronounced bend in the abdomen.^[1] It reaches sexual maturity at a length of around 18 millimetres (0.71 in), but can go on to attain a length of 26 mm (1.0 in).^[1] Its colouration is highly variable, ranging from brown or red to green, which accounts for its common name of "chamaeleon shrimp".^[2]

Praunus flexuosus is very similar to the related species P. neglectus. The two can be differentiated by the following characters:^[1]

Praunus flexuosus was the first mysidacean species ever to be formally described, when Otto Friedrich Müller described it under the name Cancer flexuosa in 1776.^[3]

Praunus flexuosus lives along the coast of the north Atlantic Ocean between 40° north and 71° north, and in the Baltic Sea.^[1] There is only one doubtful record from further south than Roscoff.^[1] It is "the only documented non-native marine zooplankton species established on the East Coast [of North America]".^[4] It was first discovered in North America in 1960, on the north side of Cape Cod,^[5] and has since colonised as far north as Nova Scotia.^[6] This colonisation may have occurred after P. flexuosus was transported as a fouling animal on ships' hulls during the Second World War.^[7] It was only discovered around the coast of Iceland in 1970, but has since proved to be common along Iceland's south-west coast.^[7] This introduction may also have been facilitated by wartime convoys (see Battle of the Atlantic).^[7]

Praunus flexuosus can tolerate salinities of 2‰–33‰.^[8] It is often found on algae, and is most closely associated with the seaweed Fucus vesiculosus.^[9] It lives in shallow water, and is often found around artificial constructions, such as docks.^[10] It is an omnivore, feeding on debris and preying on small crustaceans, especially harpacticoid copepods,^[11] but consumes a greater proportion of macrozooplankton than other common littoral mysids, such as Neomysis integer and Praunus inermis.^[12] P. fleuosus is less gregarious than species such as N. integer.^[9] When it detects a predator nearby, using a combination of visual and chemical cues, P. flexuosus hides among vegetation.^[9]

Praunus flexuosus has two generations per year. A population overwinters, and produces a spring generation that appears in May or June, before dying off in the summer.^[11] Some of the spring generation reach sexual maturity and reproduce in the autumn, producing the generation which will reproduce the following spring.^[11] Females release eggs into a brood pouch or marsupium, where they are held until they hatch.^[11]