Arthur John Thomson, The New Natural History, vol. I, Londres, Newsnes, 1926, p. 904.

..the water-vole has its ban-burrow; the lamprey grips with its circular suctorial mouth; the aquatic larvae of many insects, like stone-flies, have grappling claws at the ends of their legs; the caddis worms are often weighted with their encasement of agglutinated pebbles.
The second reason for the relatives sparseness of the river fauna…