"How do you define tool use? I came across the little octopus on a night dive. He was walking around carrying two halves of a shell with him. When threatened, he closed himself up inside the shell. Now many animals, like the hermit crab, adopt a shell for protection but in this case the octopus carried around two sides that he knew fit together. That comes close to tool use in my book.
An Ocean World Podcast about the Blanket Octopus provides an even better case of tool use. The Blanket Octopus is famous for sexual dimorphism, the male being much smaller (2cm) than the female (6ft). But the really cool thing, in my opinion, is the way the tiny male uses jellyfish tentacles. Apparently he gathers the living stinging tentacles from jelly fish, holds them between his suckers, and wields them when threatened."