PHYSIOLOGY

The donut-shaped brain of the octopus contains only part of its complex nervous system: at least two-thirds of an octopus’s neurons are actually located in the nerve cords of its arms. The arms themselves are boneless and highly flexible appendages which appear to have three excitatory neuronal inputs with fairly large synaptic input values.

Octopuses have no bone structure being invertebrates but do have a skull, a shell rudiment and a beak. Despite having no skeletal structure they are very strong and extremely flexible.

Octopi have three hearts - one that pumps blue blood throughout their extensive vascular system similar to other molluscs, and two branchial hearts which pump blood to the gills for oxygenation.

DEFENSE

Octopus defence is primary avoidance and flight but they can bite with their sharp beak, have potent venom, in some cases enough to insure or kill a human, and are very strong. When threatened the Octopuses first reaction is normally to release Ink and initiate flight.

The ability to change skin color and mimic surrounding is a great avoidance / protection skill which they utilize in self preservation as well.
In addition to using their ink sacs and camouflage via the specialized skin cells, some octopuses can autotomise their limbs which will grow back. In the case of the Mimic Octopus there is also a fourth defensive option: mimicking more dangerous animals!

REPRODUCTION

Most Octopi have similar reproductive methods. We will focus on the more known Giant Pacific (Enteroctopus dolfeini) since it has one of the longest life spans as compared to others who have shorter egg development.

When a female octopus is ready to mate she releases their equivalent of pheromones which attracts males who will sometimes fight over the right to mate with her. This chemical also helps prevent the larger male from being likely to eat the female – a common occurrence with octopi which is one reason smaller octopi often run from larger when seen.

Once accepted the male transfer’s sperm packages called spermatophores using a special structure called a hectocotylus on the third right arm.
The female stores the sperm for later use and after the male has left will locate a den which she will seal off and prepare to lay eggs.

Laying eggs one at a time and fertilizing each as it is produced the female will lay about 200 eggs into a string which she then glues to the roof of the den. Over a three week period she will normally lay about 57,700 eggs – each of which in the case of the Giant Pacific Octopus is about 5mm long with an 11mm string attached.

Over the next six months or so the female will groom the eggs and protect them. She also blows water across the eggs to ensure oxygen supply while the fetuses develop.

When hatching arrives the female will help them out by blowing water currents across the eggs to help them break free. Once free they begin swimming towards the surface of the ocean where they will feed on small planktonic animals as well as be fed upon themselves by various predators.

Like many octopi the female Giant Pacific will die shortly after her newborns arrive but the hope is that of her 57,000 plus young at least 2 will survive to continue the reproductive cycle …

SENSES

Octopi have excellent sight, smell and touch. Each of their suckers has small and touch sensors capable of identifying even the smallest of scents or hints of a food source. They are however deaf with no auditory capability at all.

Their eyes slit-shaped pupils are well suited for the light levels which an octopus typically finds itself, but they do not appear to have color vision although they do distinguish polarization of light which may explain why they can mimic surrounding colors so well.

Two special organs called statocysts attached to the brain allow the octopus to orient its body and an autonomic response keeps the eyes oriented horizontally at all times.

Octopuses have an excellent sense of touch, and each sucker has chemoreceptors to allow it to taste what it touches. Each arm also contains tension sensors to allow it to know when they are stretched out but since each limb has some independent capability and the octopuses has very poor proprioceptive senses it is not always capable of determining the exact position of its body or arms at any given time. Due to this an octopus can’t tell the overall shape of an object it is handling (stereognosis) although it can detect texture variations on a local level.

The unique autonomy of the arms causes some difficulty for octopi learning effects of its motions – to see what reaction the arms have taken to a high-level command means visually observing as there is no direct feedback to the brain from the arms themselves.

The neurological autonomy of the arms means that the octopus has great difficulty learning about the detailed effects of its motions. The brain may issue a high-level command to the arms, but the nerve cords in the arms execute the details. There is no neurological path for the brain to receive feedback about just how its command was executed by the arms; the only way it knows just what motions were made is by observing the arms visually.

© Dan Schmitt at istockphoto.com

INTELLIGENCE

Highly intelligent with levels somewhat comparable to an average housecat Octopi have shown maze and problem-solving skills that prove they experience both short and long-term memory.

Laboratory experiments have shown them capable of distinguishing different shapes and patters, and have learned to open jars and mimic other behaviour from observed actions.

© Dan Schmitt at istockphoto.com