杏吧原创

IT SOUNDS like a joke. A crab, a shrimp and a fish went into a burrow, and they left it together 鈥� doing the conga. In reality, it鈥檚 part of a rare three-way symbiosis.

Predators abound on coral reefs, so some species of shrimp and fish team up for protection: the shrimp digs out a burrow and reinforces it with bits of shell and coral, and then takes in the fish as a lodger. The fish gets a refuge, the shrimp gets an extra pair of eyes to watch out for predators.

Now of the Smithsonian Tropical Research Institute in Apartado, Panama, and her colleagues have found that some homes have a third tenant 鈥� a porcelain crab (Marine Biodiversity, ). 鈥淚t is very rare to find more than two participants in a symbiosis,鈥� says Hiller.

They found six instances of porcelain crabs sharing burrows with pistol shrimp and gobies near a reef in Lembeh Strait, Indonesia. The animals typically exit the burrow together, in a chain 鈥� with the crab鈥檚 claw and antennae touching the shrimp鈥檚 body and the shrimp鈥檚 antennae nearly glued to the fish鈥檚 tail.

If one spots a predator, it wouldn鈥檛 take long to pass on the message. The movements of the shrimp and fish may also help the crab to feed, because they disturb the bottom sediment, which could allow the crab to filter organic detritus from the water. The symbiosis is unusual because the animals are evolutionarily distant, Hiller says: 鈥淐oming from such different groups that cooperate together is something that is very rare and fascinating.鈥�

This article appeared in print under the headline 鈥淎 crab, a shrimp and a fish go into a burrow鈥︹��