We all know cephalopods from cartoons and animations. These beautiful creatures are characterized by an asymmetric body, a large head, strong, long tentacles and an organ that releases an ink-like, dark-colored substance – hence the name they are most commonly referred to by fishermen: ink-fish.
The members of the cephalopod family, all the 800 different species live exclusively in marine habitats. They can be found in all oceans and seas on Earth, from abyssal plains to shallow waters. Most species of the class live in equatorial waters, their diversity decreasing significantly towards the poles.
The class includes squids, octopuses, nautiluses and cuttlefish, all of them featuring the characteristic large head and the strong arms, in most species four or five pairs of them, that they use for capturing food. All species belonging to the class have large brains and extraordinary sharp senses. They are also the masters of camouflage – they are able to change color and texture in the matter of milliseconds and they also use their ink to protect themselves by releasing the substance into the water in order to cloud the vision of their predators. Most cephalopod species have an internal shell, with the exception of nautiluses that protect themselves with an external bony structure.
Cephalopod species move through jet propulsion. This means that they let water inside their body, then they expel it rapidly through their hyponome, a tube-like, specialized organ. This method of propelling themselves is effective only on very short distances and is very energy-consuming for the animals. Therefore, they spend most of the time just floating in the water.
All species belonging to the class have a beak-like mouth and a radula, an organ consisting of multiple rows of teeth. Cephalopod species are predators, capturing prey with the help of their tentacles. After capturing the small fish, mollusks, crustaceans or worms they usually feed on, they eject toxic juices on their prey to separate the bone of the prey from the flesh, then they take small bites of their capture.
All members of the class are characterized by rapid growth and development and short life spans. Very few cephalopod species provide parental care, which considerably decreases the survival rate of the young and the length and efficiency of the spawning is largely determined by external circumstances as well. The embryos are also very sensitive to temperature, salinity and light intensity – if the conditions are not perfect for their development, very few of them make it to adulthood.
Most cephalopod species proliferate by means of external fertilization with the exception of octopuses that use internal fertilization. The adult females release their eggs into the water, and the eggs become fertilized by the sperm released by the males. The adult females that have passed on their genetic material die immediately after the spawning is complete. Incubation time varies depending on external circumstances. In warm waters, the eggs hatch in a few days, while the eggs laid by cephalopods in colder waters can take up to a year to hatch.