EUMETAZOA: CHARACTERISTICS, TAXONOMY AND CLASSIFICATION - BIOLOGY - 2024

Eumetazoa is a sub-kingdom of the animalia kingdom that is made up of a wide range of organisms that, despite the great differences between them, also have certain characteristics in common.

Among these points in common it can be mentioned that their cells are eukaryotic, multicellular and heterotrophic. Likewise, its cells specialize in such a way that they are capable of forming complex tissues such as epithelial and connective tissues, among others.

Animals belonging to the subkingdom Eumetazoa. Source: en: User: Justin

Within this group are almost all the members of the animal kingdom, with the notable exception of the phylum porífera (sponges).

Taxonomy

• Domain: Eukaryota
• Kingdom: Animalia
• Subkingdom: Eumetazoa
• Branches: Radiata, Bilateria

characteristics

The organisms that belong to the eumatozoa sub-kingdom are very varied, however, despite how dissimilar they are from each other, it is possible to establish certain characteristics that they all have in common.

They can be diblastic or triblastic

This has to do with embryonic development. The animals of the eumetazoa sub-kingdom present a much more complex embryonic development, in which a stage known as gastrulation occurs.

It is important to remember that during the early stages of embryonic development, the blastula is formed, which is made up of an outer layer, known as the blastoderm, an internal cavity called the blastocele, and an inner cell mass known as the embryoblast.

Well, the blastula undergoes a series of transformations in a process known as gastrulation. In gastrulation, the so-called germ layers are formed. These are nothing more than a set of cells from which the different organs and tissues that make up living beings are formed.

Now, according to the number of germ layers, living beings can be diblastic or triblastic.

Diblastics

They are those organisms that have only two germ layers: endoderm and ectoderm. Within this group are the cnidarians (anemones, corals and jellyfish)

Triblastics

They are the organisms that have three germ layers, an internal one, the endoderm, an external one, the ectoderm, and an intermediate one, the mesoderm. Within this group are the protostomes, such as annelids and mollusks, as well as the deuterostomes, such as chordates and echinoderms.

They feature real fabrics

One of the most representative characteristics of the organisms of the eumetazoa sub-kingdom is that in their structure they present tissues that are specialized in specific functions.

This is because during the embryonic development stage, cells undergo a process of specialization.

In this sense, there are four types of basic tissues: epithelial, connective, muscular and nervous. Of course, depending on the evolutionary level of each animal, these tissues will be much more developed and specialized.

They present specialized bodies

Thanks to the fact that they have complex tissues such as those mentioned in the previous section, they have organs that specialize in various functions, such as: absorption of nutrients, secretion of substances, reproduction and protection, among others.

They have sensory receptors

Organisms that belong to the Eumetazoa sub-kingdom have managed to develop sensory receptors through which they are able to interact effectively with the environment around them.

This is thanks to the fact that they can perceive the different stimuli from the environment. Of course, the complexity of these receptors in turn depends on the complexity of the animal.

The sensory receptors, according to the type of stimulus they perceive are:

• Photoreceptors: they perceive light stimuli from the environment.
• Phono-receptors: they help to perceive sound stimuli.
• Chemoreceptors: they perceive stimuli of chemical origin, such as those related to the smell and taste of substances.
• Mechanoreceptors: which are activated through mechanical pressures.
• Nociceptors: they are activated by changes that cause cell damage
• Thermoreceptors: they help to perceive changes in environmental temperature.

Depending on the complexity of the animal, it may have one or another sensory organ more developed than the other. For example, cnidarians have touch receptors and photoreceptors to capture light stimuli.

On the other hand, arthropods, specifically arachnids, have simple eyes, while insects have compound eyes that allow greater visual acuity.

Flies have compound eyes. Source: Thomas Shahan

In the case of more evolved animals such as vertebrates, sensory receptors are closely related to the senses. This is how taste, touch, hearing, sight and smell exist.

Muscle cells

In eumetazoan animals, muscle cells appear, which have the ability to contract and relax. This has meant a great advance, since it has allowed, not only the mobilization of animals, but also optimization of vital functions, such as the transport of nutrients through the digestive tract and the contraction of the heart, among others.

They have a digestive cavity

The animals of the eumetazoa subkingdom are characterized by having a cavity or digestive tube, which communicates with the outside, through an opening known as the mouth opening. In the case of more complex animals, their digestive tract communicates with the exterior through two openings, the mouth opening and the anus.

Likewise, the digestive tract is responsible for the absorption of nutrients from ingested food.

They present two types of symmetry: radial and bilateral

From the biological point of view, symmetry is defined as the arrangement or location of the body parts of an animal with respect to a plane. This means that if an imaginary line is drawn through the animal, the same fragments could be observed.

There are basically two types of symmetry:

• Radial symmetry: In this type of symmetry, the parts of the body are located around a central point, similar to the spokes of a bicycle wheel. In this case, the animal can be divided through different planes, resulting in equal fragments. This type of symmetry corresponds to little complex animals, with sedentary or even sessile life habits. This is the case with cnidarians, like jellyfish, and echinoderms, like starfish.
• Bilateral symmetry: this type of symmetry implies that the animal can be divided into two equal halves by a single plane. It is typical of more complex animals such as vertebrates.

Cnidarians: animals with radial symmetry. Source: Гурьева Светлана (zooclub.ru)

Classification

The animals of the Eumetazoa sub-kingdom are organized into two large groups or branches: radiata and bilateria. This separation is based on symmetry.

Radiata

It is the least numerous group. Here the animals that have radial symmetry are grouped. It is made up of less complex and more primitive animals.

characteristics

• They are diblastic animals, that is, during their embryonic development they have only two germ layers: ectoderm and endoderm.
• Its digestive system, quite rudimentary, only has one opening, the mouth opening.
• They present radial symmetry.

Classification

This group includes the following phyla:

• Cnidaria (anemones, corals and jellyfish).
• Ctenophora.

Bilateria

It is quite a large group. It is made up of animals that present bilateral symmetry. Therefore, they are animals that are higher up the evolutionary ladder.

characteristics

• They are triblastic animals, which means that during their embryonic development they present three germ layers: ectoderm, mesoderm and endoderm.
• They present cephalization, which means that most of the sensory receptors are located in the head, where the main part of the central nervous system is located.
• Some have a body cavity and some do not. This cavity is known as a coelom and contains all the internal organs. Those that have coelom are known as coelomed and those that do not have it, coelomed. Likewise, there are some animals that are between both groups. They are what are known as pseudocoelomates. These have a cavity between the endoderm and the ectoderm, but it does not have the characteristics of the coelom.

Classification

The members of the bilateria branch are divided into two great infra-kingdoms: deuterostomate and protostomate.

Deuterostomized

In this type of animal, during embryonic development, the anus originates where the blastopore is located, while the mouth does so elsewhere. Similarly, the mesoderm of the deuterostomates has its origin from the gastrocele, a process known as enterocelia.

Within the deuterostomes, there are the following phylum:

• Hemichordata
• Echinodermata
• Chordata

Mammals: examples of deuterostomes. Source: The individual images (clockwise from the top left corner): Koala: David IliffBat: Gerald CarterDolphin: NASAEchidna: Ester Inbar

Protostomates

The main characteristic of the animals of this sub-kingdom is that during their embryonic development the mouth originates from the blastopore. Likewise, the formation of the coelom is schizocelic, which means that the cells that make it up are the product of the proliferation of cells located exactly at the junction between the endoderm and the ectoderm.

The protostomate group includes two superphiles:

• Lophotrozochoa: includes a wide variety of phyla, the most prominent being arthropods, annelids, mollusks, and flatworms.
• Ecdysozoa: composed mostly of worm-shaped animals. Among the most representative phyla, we can mention nematodes, arthropods and nematomorphs.

References

1. Barrientos, Z. (2003). Distance State University. 1st edition.
2. Brusca, R. and Brusca, G. 2005. Invertebrates. McGraw Hill, Interamericana.
3. Curtis, H., Barnes, N., Schnek, A. and Massarini, A. (2008). Biology. Editorial Médica Panamericana. 7th Edition.
4. Hanson, E. (1958). On the origin of the Eumetazoa. Sistematic Zoology. 7 (1). 16-47.
5. Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). McGraw-Hill.
6. Ivanova, O. (1998). Origin of deuterostoma in deuterostomia. Ontogenez. 29 (5). 384-385