The cephalopods are a small group of animals highly advanced and organized exclusively marine . The octopus, squid, cuttlefish and nautilus are representatives of this group. Extinct forms outnumber those that have remained alive, and as a species, it reached great diversity in the late Paleozoic and Mesozoic . Cephalopods have been among the large dominant predators in the ocean at various times in geological history.


What are cephalopods?

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


Although there are currently few living cephalopod species, they occupy a wide variety of habitats in the seas. Individual species that are often very abundant are seen as prime targets for marine fisheries .

  • Cephalopod characteristics
  • Types of cephalopods
  • Feeding
  • Habitat
  • Reproduction
  • Breathing
  • Fossils
  • Edible cephalopods
  • Examples of cephalopod mollusks

Cephalopod characteristics

Cephalopods have several characteristics, below, we will mention the most important ones.

  • All cephalopods are carnivores .
  • They have a strong beak located at the entrance to the oral cavity.
  • They have two pairs of salivary glands, one of which can be poisonous.
  • The digestive tract has three parts: esophagus , which may contain a culture; stomach , which chews food; and cecum , where the greatest digestion and absorption occurs.
  • The posterior part of the cecum has a diverticulum that is itself an ink gland, and that is capable of producing a melanin suspension that can be expelled through the cavity of the mantle.
  • Locomotion cephalopods occurs with a mechanism for propelling a jet .
  • Locomotion in other cephalopods can also be achieved by other means such as the arms and side flippers that help them to propel themselves.
  • The most important sense they have is that of sight since through it they hunt their prey.
  • Their circulatory system is closed and they breathe through gills.
  • Some may have two hearts.

Types of cephalopods

The types of cephalopods that exist are the following:

  • Tetrabranchs – They have two pairs of gills and there are only three species in the world. They are the only ones that have an external shell , formed by chambers filled with gases that facilitate and regulate their flotation. Their eyes are very simple, but they have a lens and a cornea .
  • Octopods : They have a pair of gills and eight feet , like octopuses. They have eight sucker tentacles , no horny ring , and have a rudimentary inner shell. They are bad swimmers, for example, the octopus and the argonaut.
  • Decapods : They have a pair of gills and ten feet . They have ten very prehensile tentacles , eight of which are short filled with rows of suction cups and two much longer with suction cups only at their ends. On their back they have a spongy internal limestone shell . They have a parrot beak and a radula .


Cephalopods feed mainly on small mollusks , tiny crustaceans, and small fish . On some occasions, when they cannot find food, they tend to become scavengers .


They inhabit the bottom of the ocean so many of their habitats have not yet been explored. Most of them live in salt water , although some can 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 sea zone. Some of them live at the bottom of the sea and some approach the coast during the spring. They also like to live on sandy and rocky bottoms .


Males have a testicle and a vas deferens that carry 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 responsible for transmitting the spermatophores to the female to the hectocotyl , the copulatory organ. Upon reaching this point, the male inserts his arm into the female’s paleal cavity and the sperm are then released.

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


These types of animals have gill respiration that is characteristic of beings that live 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. Gaseous exchange occurs when the filaments in the gills produce currents of water that pass over the gills.


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

Edible cephalopods

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

  • Squid rings
  • Squid
  • Squid
  • Octopus
  • Giant squid
  • Sepia

Examples of cephalopod mollusks

The most common are: squid, cuttlefish, octopus, belemnoids, nautiloids.

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