It's too cold in winter to spend a lot of time paddling around in rock pools but you can always take a few samples of seaweed home on a jar of seawater and have a look at the smaller inhabitants under the microscope. These two, each about a millimetre long, were in a sample of Corallina officinalis seaweed. The upper specimen is an unusually bristly acarine mite, found clambering through the seaweed fronds. You can see more acarine mites by clicking here.
This is a minute flatworm, with two very simple eyes, found gliding over the surface of the seaweed, propelled by thousands of cilia that are only visible at high magnification under the microscope. You can see another marine flatworm, in more detail and with a movie of the cilia in action, by clicking here.