Question

What are the special features of the seeds or fruits which are dispersed by water?

Answer 1

Plants which grow beside water often rely on water to transport their seeds for them. They may produce light seeds which float, or there may be fluff that helps buoyancy
Trees found on tropical beaches often have their seeds carried there by the sea. They have woody, waterproof coverings which enable them to float in the salty water for long periods
Mangroves are another familiar tree of tropical beaches. Their seeds are unusual in that they can begin germination while still on the parent plant, and they drop into the ocean when about a foot long. These 'sticks' float upright in the sea, waiting to be flung onto the beach to continue germinating.
Hope this helps

Answer 2

seeds and fruits have hairs