Only one species in Britain, Eubria palustris Germar, which is 2-3mm long and looks rather like a black, flattened ladybird with long threadlike antennae.  Found most commonly in the splash zone of fast-flowing water, adults are short-lived and the aquatic larvae are more commonly found.  These are known as ‘water-pennies’, due to their bronze colouration and flattened, rounded chiton-like appearance as they cling on to rocks and logs, where they eat algae.