Octopuses belong to the phylum Mollusca which includes snails,
clams and chitons. Their closest relatives are the chambered
nautilus, cuttlefish and squids. The largest and smallest
octopuses are found off the United States. The largest is
the North Pacific Octopus (Octopus dofleini) that may grow
to over 30 ft. And weighs more than 100 lbs. The smallest
is the Californian (Octopus micropyrsus) which only reaches
3/8" to 1" in length.
Octopuses have the most complex brain of the invertebrates
(animals with out backbones). They have long term and short-term memories as do vertebrates.
Octopuses learn to solve problems by trial-and-error and experience.
Once the problem is solved, octopuses remember and are able
to solve it and similar problems repeatedly.
Octopuses sense of touch is acute in it's suckers. The rim
of the cups are particularly sensitive. A blindfolded octopus
can differentiate between objects of various shapes and sizes
as well as a sighted octopus.
Octopuses have highly complex eyes which compare to human
visual acuity. Focusing is done by moving the lens in and
out rather than by changing its shape as the human eye does.
When threatened, octopuses will often try to escape by releasing
a cloud of purple-black ink to confuse the enemy. Its body will change color, release an ink cloud and
jet away to safety. Several blotches of ink can be released
before the ink sac is empty. The ink is toxic to an octopus
in a confined space such as in a cave with little water current
or in captivity. If
the the octopus can not escape the ink (or water is not changed
quickly when held in an aquarium), the octopus will become
ill or perhaps die.
Color change in octopuses is initiated by the eyes. If an
octopus is disturbed, special pigment cells (chromatophores)
in the skin will be activated in an attempt to blend in with
the surroundings. The chromatophores consist of three bags
containing different colors which are adjusted individually
until the back ground is matched. Coloration reflects mood,
white for fear, red for anger, brown is the usual color.
Many octopuses produce venomous secretions. This venom is fatal to their favorite prey - crabs
and lobsters. The tiny
Blue Ringed Octopus in Australia is deadly to humans. Its
tiny beak can even penetrate a SCUBA diver's wet suit!
Octopuses have separate sexes (male and female) and fertilization
is internal. In some species, the male can be distinguished
by modified sucker discs at the tip of one of its arms. This
modified arm is used to remove a packet of sperm from within
his mantle cavity and insert it into the mantle cavity of
the female. Within two months after mating the female attaches
strands of clustered eggs to the ceiling of her lair. The
number of eggs laid by a female varies greatly depending on
the species laying the eggs. The Common Octopus may lay 200,000 - 400,000 tiny eggs. The Pygmy Octopus lays about 150 large eggs. Once the
eggs have been laid, the female octopus will gently caress
the eggs with her suckers to keep algae and bacteria from
growing on them. She
keeps the eggs oxygenates by gently squirting them with streams
of water from her syphon. After the developing octopus turns
in the egg so the tip of its mantle is at the unattached end
of the egg and is ready to hatch, the female's gentle caresses
become more violent to help the baby octopus escape from the
egg case. Most females
will not eat after laying eggs and die soon after her eggs
have hatched. Some baby octopuses, like Octopus vulgaris,
are carried about in water currents for about a month before
they settle to the bottom. Other baby octopuses, like the
large egged Octopus joubini, look like miniature adults and
immediately start living their life on the bottom. Only one or two out of 200,000 eggs will survive to
Cephalopods (for example squids) are found in all of the world's
oceans, from the warm water of the tropics to the near freezing
water at the poles. They are found from the wave swept intertidal
region to the dark, cold abyss. All species are marine, and
with a few exceptions, they do not tolerate brackish water.
Cephalopods are an ancient group that appeared some time in
the late Cambrian several million years before the first primitive
fish began swimming in the ocean. Scientists believe that
the ancestors of modern cephalopods (Subclass Coleoidea: octopus,
squid, and cuttlefish) diverged from the primitive externally
shelled Nautiloidea (Nautilus) very early - perhaps in the
Ordovician, some 438 million years ago. How long ago was this?
To put this into perspective, this is before the first mammals
appeared, before vertebrates invaded land and even before
there were fish in the ocean and upright plants on land! Thus,
nautilus is very different from modern cephalopods in terms
of morphology and life history.
References: (James B. Wood)
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