ShrimpsCaridea

There is an animal on this reef that shoots with sound, and it is a shrimp.

A pistol shrimp has one claw grown out of proportion to the rest of it, built as a hammer and anvil rather than a pincer. When it snaps shut, the water jet leaves so fast that the pressure behind it drops below the vapor pressure of seawater and a bubble tears open in the liquid. The bubble collapses a fraction of a millisecond later, and the collapse produces a shockwave that stuns prey, a flash of light too brief to see, and a momentary temperature inside the bubble that has been measured in thousands of degrees. The sound is loud enough that colonies of these shrimps show up as permanent static on sonar, and they have interfered with submarine detection.

That is one shrimp. The group covers everything from that to the cleaner shrimp that will climb onto your hand and work at your cuticles, to species the size of a grain of rice living inside a single coral head.

What makes them worth looking for here is that most of them live with somebody else. A snapping shrimp digs and maintains a burrow and shares it with a goby that cannot dig but can see, and the shrimp keeps one antenna on the goby's tail as a tripwire while it works outside. Others live among the tentacles of anemones, immune to the stings, or between the spines of urchins, or inside sea cucumbers, or on a single species of coral and no other. Almost every conspicuous invertebrate on this coast has a shrimp somewhere on it.

They also have to shed their skeleton to grow. A shrimp splits its shell, backs out of it, and spends the next few hours soft and defenseless while the new one hardens, which is when most of them are eaten, and it is why so many of them do it inside a hole.

Macro photographers work this group harder than any other, because the shrimp does not run, the background is an anemone, and the subject is a centimeter long.