A shrimp barely 3 cm (1.2 in), orange-red with a white saddle and purple-tipped claws, riding on the back of a sea cucumber. Finding one is a matter of checking every cucumber and nudibranch on a muck site rather than searching the water.
It matches its host. Individuals on different hosts differ in color and pattern, and the same animal moved to a new host will shift over subsequent molts, which is why guides can often tell which species of cucumber a shrimp came off by looking at the shrimp.
The arrangement costs the host almost nothing. The shrimp eats particles stirred up as the host plows through the sediment and picks at the mucus and detritus on its skin, taking transport and protection in exchange for a cleaning service nobody has proven the host needs.
They live in pairs, and the pairs are stable: two shrimp on one cucumber are almost always male and female, with the larger female carrying eggs under her tail. A host with three or more is usually a large sea cucumber that has room for two households.
- small shrimp riding on the back of a sea cucumber, sea star or big nudibranch
- orange-red body with a broad white saddle, colors varying with the host
- purple-tipped claws and walking legs
- length up to 3 cm
