The Coot is actually not black but dark grey when seen close up. You can just discern that perhaps from the lit under feathers on its front here. Apart from its white features it has no other distinctive markings.
Coot have remarkable feet, not webbed like a duck, but having a kind of padding along each toe, three toes pointing forward and one back. This padding stops them sinking in to the mud whereas a duck's web feet are used as paddles. If you look in soft mud you will often see the imprints of these feet (but be careful because they could also be Moorhen's footprints). They browse for food as well as diving and dabbling.
Overall, I guess the Coot is bit of a comical bird. It can be bad tempered and very aggressive towards neighbours, especially other Coot and Moorhens. They make a honking noise like an old hand-held air horn, the ones with a rubber bubble you squeeze! To take off they run along the surface of the water flapping their wings furiously to gain sufficient speed to get in to the air.
Coot can be found anywhere there is open water, salt or fresh, but rarely on the sea. They are very common in Dorset, especially in winter as the numbers are boosted by arrivals from further north. Quite large numbers can be seen in Christchurch harbour, Poole harbour, on the River Wey at Radipole, on the Fleet and just about anywhere there is still, open water.