Octopodidae - Octopods
Octopodidae contains the majority of the octopus species of the world. They are in the Phylum Mollusca which also contains the hard-shelled bivalves and gastropods. Although their closest cousins, the squids and cuttlefishes, have retained a highly reduced semblance of an internal shell, most octopods have no internal or external shell at all. They also differ from squids and cuttlefishes by having 8, instead of 10, arms. The arms are webbed and have 1 or 2 series of suckers extending down the lower sides. In males, one of the 3rd arms is modified into a mating apparatus with a spoon-like tip and a sperm groove running up the edge of the arm. Octopods have a short life span (1-2 years). The male usually dies after mating. The female watches over her brood of eggs until the last one hatches and then dies.
Having no internal shell, the body of the octopods is highly flexible and changeable. Their skin colors are highly variable, and they can change their skin pigment to camouflage themselves by mimicking their background. They also change their skin color to communicate with other octopods. Movement though the water is by jet propulsion (squirting water through a funnel) or by flapping their webbed arms. Two species are known to walk bipedally (as on 2 legs).
Most octopods have an ink sac which produces a dark cloud in the water used to detract and confuse predators. They also have sharp beak-like mouths that can cause nasty bites. Some are poisonous. The blue ring octopus, found in Australia and Southeast Asia, is known for its venomous bite. Its saliva contains tetrodotoxin, similar to that of the puffers, that can paralyze muscles and kill the victim within hours. However, the poison is not produced by the octopus itself but by the bacteria found in its saliva.
Octopods live in holes in coral, rocks or rubble or they burrow into sandy bottoms. Their diet mainly consists of crustaceans, and their lairs can sometimes be identified by the remains of prey and other rubble scatter outside the opening. Some octopods will eat a variety of prey, including other octopods, while some will only eat one certain type of prey. A few will even eat their own species.