Basic Facts About Cephalopods

Last updated on Mon, 2010-09-13 11:28. Originally submitted by rodolfo on 2010-06-19 17:07.

Cephalopods are an ancient molluscan class of animals that include a diverse collection of more than 650 species of octopi, cuttlefish, squid and nautilus. They that inhabit every ocean and are active, intelligent marine predators that possess the most well developed senses of all invertebrates. The term Cephalopoda is derived from ancient Greek, meaning “head-footed”, because their arms are connected to their head, not their bodies; the rest of the body is in front of the head.

Body -

* Mantle: a leathery outer skin
* Mantle Cavity: visceral mass that houses the internal organs
* Modified muscular “feet”: aids movement and grasps prey; varies with each type.
* Radula: a tongue-like feeding structure equipped with rasping “teeth”

Unlike most mollusks, cephalopods lack a shell, except for Nautiluses, which are swimming snails! They are living fossils: slow, primitive and long-lived. Squid and Cuttlefish lead active lives and have internal shell-like components. Octopuses are reclusive and only become active to hunt or mate, typically hiding, motionless for more than 20 hours a day. All cephalopods have beak-like structures paired with a radula, a rasping tongue for feeding. The muscular foot of the mollusks has evolved into a siphon and arms, commonly called tentacles – 8 for octopuses, 10 for squid, and up to 90 for nautilus!

Defense and Disguise -

Cephalopods possess an amazing array of unique abilities that together compensate for the lack of armor and provide nearly perfect disguise:

* They can change the color and texture of their skin for camouflage.
* They change shape by manipulating their soft bodies.
* They produce “ink” to confuse predators.
* They jet backwards by forcing water from the siphon to escape predation.
* They have the most highly developed vision of all invertebrates, similar to vertebrates, with a cornea, lens and retina.
* They can see images, unlike other invertebrates.

Nervous Systems -

All cephalopods have well-developed nervous systems and superior senses to support active life styles and rapid movement. Although they do not see in color, they see very well in low light conditions and most are nocturnal. Their brains have distinct lobes with a brain to body weight ratio that exceeds that of fish and reptiles. They are curious animals that explore their environment and are capable of learning, and will play with objects for no apparent reason except to amuse themselves.

Size -

Cephalopods exist in an amazing range of size, from 5mm to more than 15m in length. The giant squid Architeuthis, for example, lives in the North Atlantic and is the largest invertebrate on earth. Individual tentacles may measure more than 6m long, and the eye may be 30 cm across - the size of an automobile hubcap! They swim the open ocean and have never been observed alive in the wild.

Lifespan -

Cephalopods typically have a very short lifespan, ranging from 6 months to 2 years. Smaller tropical species tend to have shorter lives while larger, cold-water species live longer. To compensate for the fast pace of their lives, they grow very fast, exhibiting exponential growth when they are young; they may increase their body weight by 10% per day! Most mollusks have very small, planktonic offspring in enormous numbers, but cephalopods have fewer and larger offspring, and some do not have a planktonic phase. Most curious, cephalopods exhibit semelparity: they reproduce once and then they die. It can be said that they live fast, and then they die!

An amazing diversity of species that possess superior senses, demonstrate masterful disguise and short, 'active' defines this group of animals. Although they may be alien compared with terrestrial animals, they are exquisitely designed for life in the sea.

See:, then scroll down to the ‘Introduction to Cephalopods’ for more information. From there you can find links to detailed information and FAQs.

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