Cephalopods - Examples, types and characteristics

2024 Author: Carl Johnson | [email protected]. Last modified: 2023-12-16 06:19

Cephalopods - Examples and Characteristics

The term "cephalopod" comes from the Greek words kepbale (head) and pous, podos (foot). They are exclusively aquatic animals, which taxonomically correspond to a class within the mollusk phylum and, although through the evolutionary history of the group, which dates back to the Cambrian fossil record, they have been more diverse, there are currently only two living subclasses, which are Coleoidea and Nautiloidea, where around 800 species are grouped.

These animals have a series of unique and diverse characteristics, which particularly make certain species peculiar and curious. We invite you to continue reading this article on our site so that you know all the characteristics of cephalopods, examplesconcrete and how they are classified

What are cephalopods?

Cephalopods are a type of mollusk, so they correspond to invertebrate animals, exclusively from marine habitats, which are generally known commonly as octopus, squid, and cuttlefish They have a long evolutionary history, with several groups that are related to them but are now extinct. On the other hand, cephalopods are anatomically distinctive, particularly for their prominent heads and the presence of arms and/or tentacles.

Types of cephalopods

As we have mentioned, the taxonomy of cephalopods is broader because they have a significant diversity of extinct groups. However, the following currently live:

Subclass Coleoidea

This subclass groups animals named as soft-bodied or shellless molluscs, which radiated into the oceans millions of years ago. In this group we find:

Superorder Decabrachia or decapodiformes: it is characterized by the presence of ten extremities, of which two are long tentacles and eight smaller arms. size.
Superorder Octobrachia or octopodiformes: they have eight arms without tentacles.

Decapodiforms include those known as squid and cuttlefish, while octopods include octopuses and vampire squid.

Overall, this subclass recognizes some 142 genera and 727 species.

Subclass Nautiloidea

In this case, there is currently only one order, Nautilida or nautiloides, with distinctive anatomical features of the group, such as its obvious external shell and the presence of between 60 and 90 tentacles without suckers, but capable of secreting a sticky substance useful for capturing food.

The only nautiloids alive today are the species known as nautilus and, although with different postures, they can be considered two genera and seven subspecies. This contrasts sharply with the diversity of extinct species, estimated at more than 2,500, who were characterized by being strong predators in their flowering season.

Cephalopods - Examples and characteristics - Types of cephalopods

Characteristics of cephalopods

Now that we know the types of cephalopods that exist and we can more or less get an idea of their main features, let's dig a little deeper to learn more about the characteristics of the cephalopods that distinguish them of the rest of molluscs:

Son invertebrate animals.
Depending on the species, sizes vary from 2 or 3 cm to around 15 meters or more in length.
The shell varies depending on the species Thus, it may be present in a modified form, since, although it can be seen externally, it is divides into internal chambers; it may be a small structure enclosed in the mantle; most of it may have disappeared, leaving only vestiges; or be totally absent. The mantle is an extension of the mollusc body that projects outwards in the form of a layer. In the case of cephalopods, it is soft and does not have a shell or, as we have said, it is enclosed in it.
Their locomotion is through a jet propulsion system, thanks to the fact that they violently expel water from the mantle by means of of a structure known as the "ventral funnel" or "siphon".
The ventral funnel is mobile, so they can control both the speed of expulsion of water, and therefore the force of the movement, such as the direction they are heading. All cephalopods have this funnel, although the shape varies by group. Thus, for example, in squid and cuttlefish it is partially included in the body, while in octopus it is completely included.
In general, are very good swimmers.
They have a series of typically muscular appendages that are located on the head and around the mouth.
The extremities, which vary in number according to the group, are useful for feeding, moving or reproducing.
Although the terms tentacles and arms are often used interchangeably, scientifically they are usually distinguished, the former being longer and more useful for capturing the food, while the seconds are shorter and help to manipulate the food. In some cases, they are covered in suckers and vary in number depending on the type of cephalopod.
They have a well-developed head, with a brain that is the most complex of the entire group of invertebrates.
A characteristic of molluscs is the presence of a muscular structure on the lower part of these animals called "foot". In the case of cephalopods, this foot is modified and is fused with the head Thus, the tentacles that are so typical in these animals derive from the foot.
They have a strongly muscular mantle, which surrounds the visceral cavity and is useful for contraction of this cavity and respiration. The visceral cavity is a chamber that forms within the mantle and where the vital organs are protected.
The mantle has an inhaling type cavity and the funnel has an exhaling function.
With the exception of the nautiluses, which have two pairs, all other cephalopods have a pair of ctenidia without cilia, which correspond to the respiratory organs, that is, to the gills. As a curiosity, they are shaped like a comb.
They have a horny beak around the mouth cavity and inside it a radula, a structure used for feeding. Although in some it is very reduced or absent.
They have two pairs of salivary glands, which in certain species can be poisonous.
The digestive system is made up of three structures: the esophagus, stomach, and cecum.
In most non-nautiloids, the last portion of the cecum consists of a structure that functions as the ink-producing gland, the which is ejected through the mantle cavity.
With the exception of nautiluses, cephalopods are characterized by the presence of cells known as "chromatophores", which allow them to exhibit various changes in color and pattern in response to situations of stress, danger or depending on the mood of the individual. This is quite a particular trait because in seconds some can completely modify their appearance, since they can also change the texture of the skin. This trait not only allows certain individuals to camouflage themselves, but even to mimic other species of animals. Meet other Animals that are camouflaged in this other article.
The nervous system is very well developed and complex, so its modes of communication respond to these characteristics.
Some types of cephalopods have been shown to acquire learning and memory, a highly distinctive trait within the group of invertebrates.
Although nautiluses have primitive eyes, the rest have very well developed ocular structures, with the presence of cornea, lens, retina and iris, so that they form images and can distinguish colors.
In general, cephalopods have a short life expectancy, which they make up for with rapid growth.

Habitat of cephalopods

Cephalopods are animals with an exclusively aquatic and marine-type habitat In general, they are not very tolerant of low salinity concentrations. However, there are a few exceptions within the group that can live in water with low s alt content. Depending on the type of cephalopod, they are distributed from surface waters and intermediate levels to important seabeds, as deep as 5,000 meters.

They have a wide global distribution, since they are present in practically all the world's oceans. However, usually increase in diversity and numbers towards the equator and decrease near the polar regions. Some tend to have free swimming habits, while others prefer to associate with rocky areas, coral formations or even towards the seabed.

Feeding of cephalopods

Cephalopods are usually active hunters, which chase and capture their prey with some ease, relying on their limbs and in some cases in the use of toxic substances and the beak, which can pierce almost anything it catches.

Depending on the species, they feed on:

Plankton
Different types of fish
Snails
Crabs
Shrimp
Copepods
Clams
Jellyfish
Worms
Carrion

It is even estimated that species of giant squid can hunt and feed on mammals such as whales. However, as they have not been studied alive in their habitat, confirmations in this regard are lacking. They have also been known to prey on members of their own group.

Cephalopods - Examples and characteristics - Feeding of cephalopods

Reproduction of cephalopods

Cephalopods have separate sexes and sometimes courtship before breeding, which may consist of particular movements between the pair and even the change in coloration, specifically in males, which is estimated to also be used as a warning for other males.

After courtship, breeding begins, which mainly consists of the following:

Sperm cells are packaged in a spermatophore, which is stored in a sac that opens into a mantle cavity. This sac is transferred to a cavity in the female's mantle which is located near the oviduct. To do this, they use a specialized arm known as a "hectocotyl."
When the eggs reach the oviduct area is when fertilization occurs. Once fertilized, the eggs are deposited or attached to some substrate, which can be rocks, corals, clumps of plants or algae.
Cephalopods, with the exception of the octopus species, do not care for their eggs The latter are very sensitive to temperatures, but also the general conditions of the water and even pollution can affect embryonic development.

Cephalopods, on the other hand, do not have free larval development, that is, after embryonic development, hatching of the egg occurs, from which a fully formed young individual emerges. Since the embryo begins to develop, the head and foot are no longer differentiated, and from the anterior edge of the latter, the tentacles around the mouth are formed.

On the other hand, these animals usually exhibit a series of complex behaviors for reproduction, which as we have mentioned not only include courtships, but also strong confrontations between malesIn these confrontations we find the use of a washing technique used by the second male who tries to mate with the female and tries to eliminate the sperm that has been introduced from a rival. It has also been identified how some males manage to modify their appearance to show themselves as females and avoid being attacked by stronger males.

Examples of cephalopods

We mentioned that cephalopods are commonly known as squid, cuttlefish, octopus, and nautilus. However, below we will name some examples of specific species to better understand the types of cephalopods: