Cephalopods

Scientific name : Cephalopoda

The class Cephalopoda includes octopuses, cuttlefishes, squids. Those ranks amongst the most interesting animals to be watched at, mainly for their complex and variate behaviour. Many Indo-Pacific species are rare and only recently discovered. Some, being already popular for the divers, still have no scientific name.
Octopuses, cuttle fishes, squids, belong to the phylum Mollusca, class Cephalopoda. Those are soft bodied animals, with a head (1), a body (2) containing the guts (and shell in some species), and 8-10 tentacles (3), very mobile and equipped with suckers. The mouth is in the middle of the arms, it contains a hard beack and a toothed tongue (radula). In many species the beack is connected with a venom gland.
In the order Nautiloidea, a large external shell exists, divided into chambers. Also the orders Sepiida and Teuthida (cuttlefishes and squids) have an internal shell used by the former for idrostatic balance adjustements (it is divided into small chambers, that can be filled with gas, transported by the blood, making the whole animal more buoyant), while in squids is used only to make the body more rigid and hydrodinamic.
In the order Octopodia (octopuses) the shell is missing. The body is soft, allowed to enter the smallest holes. Squids and cuttlefishs are good swimmers, octopuses are better fit for benthic life.
The eye (4), is very similar to a vertebrate eye and very effective. Behind the eye a funnel (5) can be seen, used to drive the water inside and outside a gills chamber, and is also used for movement, in a sort of jet propulsion.
There are cephalopods in all the marine environments. Octopuses are mostly benthic, they live in all the reef environments and in bay. Cuttlefishes live in the same environments; even if they move swimming rather than crawling, they can disappear burying themselves completely in a sandy bottom. The shell (cuttlebone) allows a buoyancy control, that makes the animal neutrally buoyant (for swimming) or negative (for hiding in the bottom). Squids are open sea animals, only few species can be seen close to the reef. Many cephalopods live in very deep water, and they are very poorly known.
All cephalopods are predators, mainly on crustaceans and fishes, that they catch using the tentacles and kill using a venomous bite.
When mating, the male uses a modified tentacle (ectocotile) to transfer the sperms to the female.
In many species the eggs give birth to a young animal, very similar to the adults. In other species a transparent larva, after phases of planktonic life, through a metamorphosys gets the final adult look. In the film the rare images of a large benthic Octopus larva (maybe Octopus cyanea), brought next to a sandy bottom by the currents and close to metamorphosys.
It is unlikely to confound a cephalopod with anything else, their anatomy is unique. The shell alone could be confused with a gastropod's shell, sometimes. The main difference is that the cephalopods shells, when spiral shaped, are planar, the gastropods shells are elongated.
Cephalopods are very efficient animals. They can manipulate objects thanks to their mobile tentacles and to the many suckers. They have a very good sight. But maybe their more streaking feature is their capability to change colour and shape.
Their skin contains pigmented cells (cromatophores), each one connected to muscular fibres, that can extend or contract the cell, changing the colour very quickly. Nerves transmit the stymulus to each cell, allowing the animal to change colour and to assume complicated colour patterns in no time.
Other muscular fibres can smoothen the skin or make it rough, to better conceal the animal on the bottom.
Colour changes are used for camouflage, but as well to communicate with the other animals of the same or different species, to intimidate, confound, subject.
Another system to generate confusion in predators is the ink secretion, that can be quickly expelled while the animal changes direction. Due to its density, it becomes a false target attracting the predator and allowing the mollusk to escape.