Octopuses are cephalopod mollusks characterized by having eight arms, no tentacles, and the internal shell lost or considerably reduced. There are over 100 species of octopuses (Genus Octopus) in the world as well as numerous species of deep-water and pelagic octopuses (Order Octopoda). Our knowledge of octopuses comes almost entirely from only a few species (Octopus vulgaris, O. bimaculatus, Enteroctopus dofleini, Eledone cirrhosa).
The species known as Octopus dofleini, the Giant Pacific Octopus, has recently be re-classified as Enteroctopus dofleini (Hochberg 1998). The genus Enteroctopus includes the other giant octopuses of the world (E. dofleini in the north Pacific, E. megalocyathus off S. America and E. magnificus off southern Africa).
Enteroctopus dofleini is the largest species of octopus in the world. Although it is very unusual to find an individuals over 100 pounds (45 kg), one large individual captured just near Victoria, British Columbia in 1967 weighed 156 pounds (70 kg), and was almost 23 feet (7.5 m), from arm tip to arm tip. There are records that seem to be well-referenced of a few individuals that were more than 300 pounds (136 kg) and one that was more than 400 (182 kg). (Ref: Dr. F.G. Hochberg, Santa Barbara Museum of Natural History).
Enteroctopus dofleini occurs on the continental shelf of the north Pacific ocean, where its range extends from southern California, north along the coastline of the Pacific Northwestern Americas, across the Aleutians, and south to Japan. The species occurs at depths from the intertidal to 750 m.
Enteroctopus dofleini live 3-5 years. When mature, females lay eggs on the inner side of a rocky den and may lay 20,000 to 100,000 eggs over a period of several days. Eggs are tended, cleaned and aerated by females until they hatch. Incubation takes 150 days to seven or more months, depending on the temperature. Females do not feed while tending eggs and die when the eggs hatch or shortly thereafter. Many of the eggs will die if not tended by the female until hatching.
Following hatching E. dofleini swims toward the surface and spend 4-12 weeks drifting in the plankton until they reach a size of >14 mm mantle length (still under 5 grams.). The young then settle to the bottom, although not much is known about this settlement phase.
Dens are an important resource to octopus during all benthic life stages. Dens are used both as brooding chambers and as refuges from predators, including other octopuses, various fishes, and many marine mammals. Most dens of juvenile E. dofleini are naturally occurring spaces under rocks or in crevices or are an excavated cavity in sand or gravel under a boulder.
Octopuses consume mostly crustaceans and mollusks, most often small crabs and scallops. Other bivalves, snails, fish and other octopus are also eaten.
Octopuses use three different techniques to gain entry to hard-shelled prey: they may pull it apart, bite it open with their beak or 'drill' through the shell. Prey that are difficult to pull or bite open are drilled: secretions from the salivary papilla soften the shell of the prey, and the softened material is then scraped away with the radula to create a tiny hole in the shell. Through this hole, the octopus secretes a toxin that paralyzes the prey and begins to dissolve the connective tissue. The prey is then pulled apart and consumed.
The third right arm of the male octopus is hectocotylized with a modified tip, called the ligula, that is used during mating, and in E. dofleini may be one fifth the length of the arm. Males may mate with more than one female and females receive fairly large spermatophores (up to 1m long) during mating. Eggs are laid some time after mating (one report of 42 days in captivity in Hartwick, 1983).
The mouth is located at the center of the arms. Octopuses have a strong, parrot- like beak contained within the buccal mass, the muscles which work the beak and tongue.
Mature female E. dofleini have 2240 suckers, 280 on each arm, but males have fewer because there are only about 100 on the hectocoylized arm. (Toll, R. 1988. "The use of arm sucker number in octopodid systematics (Ceph.: Octopoda)" American Malacological Bulletin. 6(2):207-211. 1988). In at least shallow-water species of octopuses there seems to be a species-specific number of suckers per arm that is reached at a size less than the maximum size, with the number on the hectocotylus also species-specific. In the deep-water species, this doesn't necessarily hold.