The aglae fell on the sand and everyone except the teacher gasped. On the back of the new student were… real… suckers.

– Wow! They are cute! I want such suckers, too! How did you grow them? – Smelt blurted out in one breath, – share them with your friends right now!

– Our Octa needs suckers in order to stick to the belly of a shark, – the teacher answered, – with the help of this unique suction cup her relatives stick to any large fish or large sea animal and swim using «free transportation’' which is both convenient and safe.

– They eat what predators haven’t eaten up, – Jocky shouted from his seat.

– Not at all! – the new student was offended and pouted her lips, – we, we… feed on planktonic organisms.

– Is this also symbiosis? asked Hamsa.

– Alas, it is not. Miss Swallow tapped the stone with her tail, calling everyone to silence… she wanted to add something else, but a living bush tumbled groaning into the classroom.

– Let me introduce myself – Basil, the Hermit Crab, and on my back I have my best friend Basilia anemones. We have been living together for many years… I …am… Well, excuse my bad memory, I forgot what I wanted to say…my old age, you know.

– Children, here is an example of «obligatory ‘’symbiosis, – the teacher continued answering for the guest, – first, completely different sea creatures find each other, then the crab «persuades» the sea anemone to move to its back. Poisonous Basilia protects him from parasites and predators, and Basil travels with her along the seabed, making it possible to find more food. Admit that, waiting for a long time for something tasty to swim by you is worse than coming to the delicacy yourself, and not walk, but ride on your friend’s back!