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Molluscs of Australia

Cephalopods - Biology of Octopuses  


Octopuses are considered to be the most intelligent of all invertebrates . They have a highly complex nervous system, only part of which is located in its brain. Laboratory experiments with mazes and problem-solving have shown that they do have both short-term and long-term memory. Their arms show a wide range of complicated reflex actions. Some octopuses, such as the mimic octopus, will move their arms in ways that copy the movements of other sea creatures.

The octopus is the only invertebrate which has been proven to use tools. The Veined Octopus (Amphioctopus marginatus) has been filmed gathering coconut shells, manipulating them, and then reassembling them to use as shelter.


Octopuses have the ability to hide in very small spaces, change their colour (camouflage), shape (mimicry) and apparent size, and to modify their environment to suit themselves. They also have other defenses to use once they have been seen by a predator. The most common is fast escape using jet propulsion. Other defenses include using ink sacs and dropping limbs, The crawling arm can distract the potential predator.

Mimic Octopus
Octopuses are thought to be one of the most intelligent invertebrates and can
change the color and texture of their skin to blend in with rocks, algae, or coral
to avoid predators. But until now, an octopus with the ability to actually
assume the appearance of another animal had never been observed.

Blue ring octopus


Octopuses are intelligent active predators. They eat small fish, molluscs and crustaceans. They use their sharp parrot-like beaks to crush the shells of their prey. To prevent their prey fromescaping, they have modified salivary glands that produce a poison (venom). Although all octopuses produce venom only the the small blue-ringed octopuses are deadly to humans.

Many octopuses leave piles of debris consisting of shells and carapces of their prey. These are known as ‘middens’ around the entrance of the protective lair in which they live.

The main predators of adult octopuses are some large fish, moray and conga eels, seals, dolphins, sharks and orca whales. Large numbers are also caught for food by humans.

Octopus tentacle showing suckers
Image from Tamburix
from Flickr

Life span and Reproduction

The life span of octopuses is short, rangiing from six months for small species to three years in larger ones.

When octopuses reproduce, the males use a specialized arm to insert packets of sperm into the female's mantle cavity. Males die within a few months of mating. In some species, the female octopus can keep the sperm alive inside her for weeks until her eggs are mature. After they have been fertilized, the female can lay up to 200,000 eggs.

The eggs are hung in strings from the ceiling of the female's lair or they are individually attached to asolid surface depending on the species. The female cares for the eggs, guarding them from predators and gently blowing currents of water over them to increase the oxygen supply. She does not hunt during the roughly the month spent taking care of the eggs and may eat some of her own arms forenergy. When the eggs hatch, the mother leaves the lair and is too weak to defend herself from predators.

Newly hatched octopuses live amongst the plankton and eat copepods and larval crabs and starfish.

The largest octopus species is probably the North Pacific Giant Octopus, (Enteroctopus doflein) weighing, on avaerage, around 15 kg with an arm span of up to 4.3 m. the octopus that has been discovered is the Octopus Wolfi, which reaches 1.5 centimetres in length and weigh less than one gram.

Sea Lion Attacks Octopus: An Epic Battle
An Australian Sea Lion attacks and eats a huge octopus in South
Australia. These amazing images were captured using National
Geographic's Crittercam in collaboration with the South Australian
Research and Development Institute (SARDI).

Senses and Movement

Octopuses have excellent eyesight and a very well developed sense of touch. Octopuses move about slowly by crawling, walking on their arms, or by swimming or by using jet propulsion to move very fast for short distances.

Octopus sashimi

Eating octopus

Octopus is eaten in many countires. It is very popular in Japan, where it is often served raw, and around the Mediterranean and Portugal. The flesh needs to be tenderized by pounding it before it is cooked.

The Sydney Octopus (Octopus tetricus) is an
exceptionally common species in Australia along
the New South Wales coast.It can be commonly
found in amongst rubble in the sponge gardens
and seagrass beds of coastal estuaries where
they can be found hiding in their lair.

A species of octopus has been found to use coconut shells as tools to hide from potential threats.



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