You would know the ‘true’ octopus if you saw it, wouldn’t you?
Reading a book about Mediterranean seafood, Luiz learned that according to an authoritative Italian cook book, the true octopus has a double row of suckers on each tentacle, as opposed to the single row you find on the all together inferior sinisco (diminutive: sinischiello). The sinisco lives further out to sea and is normally captured by boats with nets. The true octopus is attracted by the colour white and can be lured by a white feather or rag, placed in the centre of a small five-pronged anchor call a filatiello.
Similarly using white as a lure is a white-painted amphora filled with white stones, lowered on a rope to the bottom of the sea, near a rock. The true octopus will empty the stones out and ensconce himself inside it as in a nest. The fisherman, seeing white pebbles around the amphora, hauls it up and has captured his octopus.
The amphora has the glorious name of mummarella.
Source: Alan Davidson, Mediterranean Seafood, 2nd edn (Baton Rouge: Louisiana State University Press, 1981), p. 339