Around a quarter of the described species are found in fresh water, however, including almost all the members of the species-rich family Atyidae and the Palaemonidae subfamily Palaemoninae.

[2] Except where secondarily lost, shrimp have one pair of stalked eyes, although they are sometimes covered by the carapace, which protects the cephalothorax.

Many cleaner shrimp, which groom reef fish and feed on their parasites and necrotic tissue, are carideans.

[2] In turn, carideans are eaten by various animals, particularly fish and seabirds, and frequently host bopyrid parasites.

The post-zoeal larva, often called a decapodid, resembles a miniature adult, but retains some larval characteristics.

The decapodid larva will metamorphose a final time into a post-larval juvenile: a young shrimp having all the characteristics of adults.

[6] Shrimp of the infraorder Caridea are more closely related to lobsters and crabs than they are to the members of the sub-order Dendrobranchiata (prawns).

The easiest practical way to separate true shrimp from dendrobranchiates is to examine the second abdominal segment.

The below cladogram shows the internal relationships of eight selected families within Caridea, with the Atyidae (freshwater shrimp) being the most basal:[14] Atyidae Oplophoridae Lysmatidae Barbouriidae Thoridae Hippolytidae Alpheidae Palaemonidae The infraorder Caridea is divided into 15 superfamilies:[12] The fossil record of the Caridean is sparse, with only 57 exclusively fossil species known.