The cephalopods are a small group of highly advanced and organized animals, exclusively marine. Octopus, squid, cuttlefish and nautilus are members of this group. The extinct forms surpass in number those that have remained alive, and as a species, has reached a great diversity at the end of the Paleozoic and Mesozoic. Cephalopods have been among the large dominant predators in the ocean in different moments of geological history.


Related topics

Bivalves, gastropods, nematodes, flatworms

What are cephalopods?

They are a group of marine mollusks that have a sack with an open space where their head comes out. They are the largest invertebrates on earth and have a series of tentacles.

Although there are currently few species of live cephalopods, they occupy a wide variety of habitats in the oceans. Individual species are often very abundant, and they are seen as main targets for marine fisheries.

Characteristics of the cephalopods

Cephalopods have different characteristics, here are the most important ones.

Types of cephalopods

The types of cephalopods that exist are the following:


Cephalopods feed mainly on small mollusks, tiny crustaceans and small fish. Sometimes, when they cannot find food, they have to become scavengers.


They inhabit the bottom of the ocean and thus, many of their habitats have not yet been explored. Most of them live in saltwater, although some may live in fresh water. The few cephalopods that manage to adapt to the soil need a lot of moisture to survive.

They can be found throughout the world regardless of the type of zone or the sea zone. Some of them live at the bottom of the ocean and some, approach the coast during spring. They also like to live on sandy and rocky bottoms.


Males have a testicle and a vessel that carries sperm to the seminal vesicle. Females have an ovary and an oviduct with the oviductal gland. Before copulating, they make a previous courtship to realize that they belong to the same family. The male is in charge of transmitting the spermatophores to the female towards the hectocotyli, the copulating organ. At this point, the male introduces the arm into the female’s paleal cavity, and the sperm are then released.

The female’s eggs are deposited in the form of cords on the seabed. After reproduction, the parents die.


This type of animal has a gill breathing that is characteristic of beings living in the sea, where there is little oxygen concentration. These gills are located in the paleal cavity and have blood vessels. They can also be single, double or quadruple. The gas exchange occurs when the filaments that have the gills produce water currents that pass over the gills.


Cephalopods are quite complicated mollusks and appeared in the Cambrian period, so they arose more than 500 million years ago. The history of their evolution has been well documented since most of the forms had a mineralized shell that was easily preserved in the fossil record. Spain is where most fossils have been found.

Edible cephalopods

Some of the cephalopods that can be used as food sources are the following:

Samples of cephalopod mollusks

The most common are squid, cuttlefish, octopus, belemnoid, nautiloid.

Written by Gabriela Briceño V.

How to cite this article?

Briceño V., Gabriela. (2019). Cephalopods. Recovered on 23 February, 2024, de Euston96:

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