Cuttlefish are marine cephalopods belonging to the order Sephioidea. There are at least 120 different species of cuttlefish, and the modern cuttlefish first appeared somewhere around 21 million years ago. They get their name from their thick internal calcified shell known as a cuttlebone. This cuttlebone assists with buoyancy by filling and emptying its various chambers with gas. Depending on the species, cuttlefish can grow to be 15 to 50 cm in length. All cuttlefish have nearly flattened bodies surrounded by a pair of narrow fins, w-shaped pupils, eight arms and two longer tentacles. The fins undulate rapidly when swimming. Suction cups are located on both the arms and the pads at the tips of the tentacles. The longer tentacles are used for capturing prey and can withdraw into two pouches when not in use. They are carnivorous with a diet of crustaceans, small fish and sometimes other cuttlefish.
They live in tropical and temperate waters, moving to deeper waters in the winter. Many can be found in the Mediterranean, North and South Baltic Seas, East and South Asia coasts, Philippines, South Pacific, Africa and Australia. They are nearly absent from the Americas. Cuttlefish are much more social than other cephalopod species. When mating or fighting with other cuttlefish, these cephalopods will “flash” different colors. They’ll show an impressive display towards other male cuttlefish as a show of dominance, or a calm display towards potential mates. Some male cuttlefish will actually change their colors to disguise themselves as females. This way, they may sneak past the other males and mate with the females. Cuttlefish also use this color changing ability to camouflage themselves when hunting. They may also change to their shape to mimic something, like a coral head, when avoiding detection. Like squid and octopus, they can eject ink to escape from predators. Their primary predators are larger fish, sharks, other cuttlefish and humans to an extent.
Cuttlefish live a very short lifespan of only one to two years and have year round reproductive cycles. Mating seems to occur most often during the months of March and June. Researchers can observe all the developmental changes and life history in a much shorter timeframe as a result. Cuttlefish have one of the largest brain-to-body size ratios of invertebrates. They are clever and capable of even learning to navigate through a simple maze. Still, there isn’t as much research on cuttlefish as there is on their more charismatic cousin, the octopus. Humans do consume cuttlefish as well as utilize their ink. The cuttlebone is also a source of calcium for cage birds. For the time being, there are no major conservation concerns for cuttlefish.