Not for the squeamish. Modern-day cephalopods are rarely, if ver, top predators in their environment. Most modern-day cephalopods must therefore rely on other means to avoid being eaten. This includes sharks, bony fishes, marine mammals and seabirds, as well as other cephalopods. Most of the cephalopods' defences are therefore visual in nature.
Many predators also employ other senses when hunting, such as smell or a lateral line system.
Often the keen senses of cephs will enable them to notice an approaching predator long before it comes close enough to do real damage. Once they have spotted a predator, the first reaction of many bottom-living species such as cuttlefish and octopuses is 'trying to look like the surroundings' by changing their colour and even the texture of their skin. Squids that live in midwater have fewer options, but they also employ colour changes, for instance in countershading when the squid adjusts its colour to the ambient light environment. By doing this, the squid effectively takes on he same brightness as the surrounding water when seen from above or below. Many species of squid that live in deeper waters use bioluminescence to a accomplish the same goal.