The cuttlefish (Cephalopoda) are a class of animals belonging to the family of molluscs (Mollusca). The scientific name, Cephalopoda, is derived from Greek and literally means cephalopods. This name was chosen because the arms are in a circle around the animal’s mouth.
Cuttlefish are only found in salt water and live in all the world’s oceans. They are able to change color. Most squid are fast growing and short-lived, usually only living for one to two years, with the exception of several deep-sea and polar species and the nautiluses which can live much longer.
They move forward by pumping water into their mantle, which they forcefully squeeze out again, along the siphon. All squids are carnivores. The food consists mainly of fish, crabs, lobsters and molluscs that they catch with the suction cups on their gripping arms. They would also occasionally engage in cannibalism.
Cuttlefish are characterized by the position of their arms around their mouths. They have eight arms with suction cups, cuttlefish and squid have two feeding tentacles above them. The only exception is Nautilus pompilius which has about 90 tentacles without suction cups.
Cuttlefish have well-developed eyes with a torus-shaped brain surrounding the intestinal tract. They have a hardened parrot-like mouth, on top of that most species also have a rasp tongue (the so-called radula) to tear the prey into pieces. The intestines and delicate organs are located in the mantle (the fried rings are vertical slices of this mantle). The squid takes oxygen from the water with the help of gills (2 to 4), water is sucked in by the rhythmic movement of the mantle and then removed again through the siphon. This siphon is also used to spray ink and for excretion.
Many squids have some form of a shell: the Nautilus has a completely external shell (much like the extinct ammonites). Some species (such as Spirula spirula or the cuttlefish) have an internal shell. But in the octopus, the shell is reduced to a few small pieces inside the body. Other species no longer have a shell at all.
Cuttlefish are a very old and successful group of animals. Presumably they originated about 500 million years ago in the Cambrian. The first species were often small (2 cm), but there were species whose shells had a diameter of 3.5 meters. In subsequent eras, the squid evolved. About the middle of the Ordovician, the first ancestors of the Nautilidae arose. The subclass Coleoidea, which contains all other living squid species, did not arise until later, 350 million years ago. This also explains why the Nautilus is so different from the other living squid species. Not much is known about the evolution of the squids that still live today because their soft bodies often do not fossilize, usually only the shell fossilizes. But not every species has a shell and in some species it is also very soft and brittle, so that it does not fossilize easily.
All squids reproduce with eggs. The eggs are fertilized by the sperm of the males (which can be applied to the female in various ways). Fertilization can take place in the ovary, in the fallopian tubes and also outside the body. The number of eggs a female squid can produce ranges from about 30 to 500,000. Some species care for their eggs (such as the common octopus, which usually dies of exhaustion after hatching), others do not care for their eggs at all. Newly hatched squid, however, are always on their own and grow up without the help of their parents.
An almost perfectly camouflaged blue-ringed octopus (genus Hapalochlaena), note that the squid imitates the structure of the environment with its skin.
The squid’s body is soft and fragile, so most squids have different techniques for camouflage or distracting predators. The best-known distraction technique is spraying with ink. All squid can do this, except the Nautilus and several deep-sea species.
Most squid can also change color. This is done with the help of special cells in the skin: the so-called chromatophores, which produce different colors depending on the degree of stretching (from reddish-brown to red and pale yellow-orange). Furthermore, it happens through the iridocytes (or iridophores) which can produce white, green and blue through refraction and through the reflection, the iridocytes are located in the skin under the chromatophores. Some squid also have leucophores, which are layers of cells that reflect the dominant color in the squid’s environment: in white