Many crustaceans are classified as shrimp, animals that resemble lobsters but are much smaller. The term shrimp is not a scientific one but refers to a group of small crustaceans that have 10 jointed legs on the thorax and swimmerets on the abdomen. Unlike lobsters, shrimp are primarily swimmers instead of crawlers. Several species of shrimp live on the reef. The banded coral shrimp (Stenopus hispidus) and the painted dancing shrimp (Hymenocera picta) are two representative reef residents. Several species of mantis shrimp also make their homes there.

Hymenocera picta (The Dancing Shrimp)
Hymenocera picta (The Dancing Shrimp)

Mantis shrimps are longer than most other types of shrimp. These crustaceans, which are often vividly colored, are fierce and voracious predators. Depending on the species, their second pair of claws are modified into one of two forms: spears or clubs. Those with clubs smash the legs of their prey to stop them, then crack open their bodies. This action is similar to the way a preying mantis attacks and accounts for the group’s common name. The types that have spear-shaped claws use them to stab fish.

Mantis shrimps known as snapping, or pistol, shrimp have one enlarged claw that can snap shut with enough force to sound like a pistol shot. This unique snapping behavior serves two purposes: to warn trespassers to stay away or to stun prey, slowing them for a moment so that the shrimp can grab them.

Depending on the variety, pistol shrimps may have symbiotic relationships with fish, sponges, corals, or anemones. One species sets up housekeeping with gobies, small fish that are less than 4 inches (10 cm) long. In this association, the shrimps, which is an accomplished digger, creates and maintains a burrow in the sand. Because the shrimp's has poor vision, it is in danger of wandering too far away from its burrow when predators are nearby. The sharp-sighted goby has no trouble keeping an eye out for danger, and it uses the shrimp’s burrow as a base of operations. The goby spends its day hovering at the entrance of the burrow, occasionally dashing out to grab prey. When danger approaches, it backs into the den, warning the shrimps to do the same. The shrimps gets information from the goby by maintaining unbroken contact, constantly touching the little fish with its antennae and legs.