Evolution alone is an amazing thing – but species that evolve together can be all the more spectacular, protecting, feeding and cleaning one another in incredible ways. Sharks pair with fish, fish with shrimp and shrimp with sea cucumbers and much much more. From boxing crabs that wield poisonous anemones as weapons to shrimp that scour the mouths of electric eels, here are seven of the most radical symbiotic relationships from the shallowest to the deepest waters of our world.





The cleaner shrimp seems foolhardy, climbing into the open mouths of sharp-fanged eels to dig around for food. These photos seem to depict daring shrimp shortly before their demise, but actually show an ancient tradition of cleaning. Moreover, these shrimp have evolved beyond merely finding eels and fish in order to eat their mouth parasites: they congregate at ‘cleaning stations’ in vast numbers. And yes, if you are looking for an alternative dental hygienist, they will even clean your mouth.

(Images via: Flickr, AZAquaCulture, AquariaWorld, DeeperBlue and Diver)

Boxing, hermit and other crabs have found that they make friends with strange benefits in various species of stinging sea anemones. Boxing crabs (above, top) hold on to anemones and wield them like deadly pom-poms, warding off potential predators with their poisonous pals. Some hermit crabs (above, bottom) lift anemones and attach them to their shells in order to dissuade attackers. These relationships go both ways: the anemones are able to pick up more food as they move through the water with their shelled allies.

(Images via: OutbackPhoto, UWPhoto, GuamShellClub and NyTimes)

A happy-looking spotted fish living with a hard-nosed shelled shrimp: it sounds like something from made-for-kids animated movie. However, the goby and their shrimp buddies are truly contented cohabitants. They occupy holes together dug by the shrimp and protected by the goby. The relatively blind shrimp rely on their strong-sighted goby door guards to signal them about when it is safe to move. The gobies, in turn, rely on the burrowing shrimp to have a safe place to hide and sleep.

(Images via: Wikipedia, GreenWater, Infiltec, DaveJenkins and MMcFCuba)

Sharks seem like the most unlikely allies of the ocean: huge, speedy, vicious and ruthless predators – so why are they so tolerant of remora fish using strange stickers on their heads to attach to attach to the shark’s underbelly. This was initially thought to be a case of commensalism – a relationship in which one species benefits and the other gains nothing – but it is now widely thought that the remora not only picks up the scraps after a shark has a meal but also cleans the parasites from its underside.

The anglerfish is one of the most infamously ugly and unbelievable deep-sea swimmer, luring unsuspecting victims into is gaping toothed mouth. How does it accomplish this feat? With the promise of a small glowing prey that is, in fact, millions of glowing bacteria attached to a fishing-pole-like protrusion from its forehead. Disturbing side note: to mate, a male angler bites a female slowly dies and shrivels to a pair of gonads and is carried around by the female until she is ready to mate with his remains.

(Images via: Sulawesi, Diver, EcoDivers and PhotoNet)

Wait, yet another shrimp? The appropriately named emperor shrimp, however, is one that benefits more than its partners from its relationships with them. While it is not a parasite, its rides gain no real advantage from having a shrimp cruising around on their backs. These hitchhikers of the sea can be found on top of much larger and faster-moving creatures including nudibranchs and sea cucumbers. They hang off the sites and pick up scraps from the dirt as their mounts move about the sea floor.

(Images via: PhotoEnvisions, Wikipedia and Flickr)

The clownfish is virtually the only species of fish that seems able to resist the toxic effects of sea anemone poison, moving through them unharmed. The anemones protect them and they eat the leftovers from fish on the anemone including copepods, isopods and zooplankton. They also fiercely protect their territory, keeping individual anemones to themselves in small gender-switching self-sufficient groups. Remember Finding Nemo? In real life, Marlin would have turned female after Nemo’s mother died.

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