Spanish cedazo means ‘an instrument consisting of a cylinder with a cloth stretched across the bottom of it that serves as a sieve.’ The word evolved from Latin saetaceum ‘a sieve, strainer.’ That was based on saeta or seta ‘a thick, stiff hair; a bristle,’ so it’s clear that the Romans used animal hair to make the screens in some of their sieves. Biology has borrowed seta in its Latin sense but has also extended it to ‘the stalk of a moss capsule.’ The English adjective setaceous means ‘made of or having bristles.’
In contrast, and spelled with an initial c-, yet still based on the same Latin original, the adjective cetáceo/cetaceous designates ‘any of the mammals in the group that includes whales and porpoises,’ from the fact that some of those animals have sieve-like structures in their mouths to get food by filtering tiny creatures out of the water they swim through.
Darwin used the word in his 1839 book The Voyage of the Beagle, when he spoke of the strange fact that such enormous mammals subsist on such small organisms: “If we suppose the case of the discovery of a skeleton of a Greenland whale in a fossil state, not a single cetaceous animal being known to exist, what naturalist would have ventured conjecture on the possibility of a carcass so gigantic being supported on the minute crustacea and mollusca living in the frozen seas of the extreme North?”
© 2011 Steven Schwartzman