Also called optional mutualism or not required symbiosis, protocooperation is an optional association between individuals, in which both species benefit, but one can live independently of the other. Eg Sea Anemone and Paguro, cattle and anum (tick cleaning), African crocodile and toothpick (oral hygiene).
On the banks of the Nile River in Africa, ecologists have realized that there is a unique example of protocooperation between the dangerous crocodiles and the sublime stick bird. During the nap the giant crocodiles open their mouths allowing a small bird (the stick bird) to collect food scraps and small worms from its powerful and strong prey. The relationship was typically regarded as an example of commensalism, as for some only the bird benefited. However, the removal of parasitic worms makes the crocodile a beneficiary in the relationship, which characterizes the protocooperation.
Another example is ox and anum. Oxen and cows are commonly attacked by external parasites (ectoparasites), small arthropods commonly known as ticks. And the black anum (Crotophaga ani) has as a favorite meal these little parasites. The relationship is beneficial to both (the ox gets rid of the parasite and the anum feeds).
Hermit crab and sea anemone - The hermit bern is a crustacean of the genus Pagurus whose main characteristic is that it has a fragile abdominal region, because the exoskeleton does not have the same resistance as the cephalothorax. This crustacean when reaching the adult phase (still in the process of growing, therefore making the seedlings) looks for an abandoned gastropod mollusk (snail), and settles inside it. In a way the crustacean remains protected. However, some predators still manage to remove the Pagurus from inside the shell. That's where the sea anemone comes in, a cnidarian.
Like all cnidaria (or coelenterates), the sea anemone is endowed with structures that release stinging substances in order to defend themselves. The association benefits both anemone and Bernardo: Bernardo gets protection when an anemone settles on his (borrowed) shell because no predator comes close. Anemone, on the other hand, benefits because its food "menu" improves a lot when "ride" on Bernardo's shell. The anemone usually picks up its food (particles) through its numerous tentacles, waiting for them to pass by. In Bernardo's ride there is a significant increase in the feeding field for anemone.
Hermit with anemone stuck in its shell.