Cnidarians: characteristics and examples

The cnidarians are aquatic organismsmost of them marine, and make up the Cnidary Filo. More than 10,000 living species of cnidarians are known and there are also fossil species dating from the ordovícido.

These are the main characteristics of the Cnidarians or Cnidaria:

• They are diblastic organisms: That is, your body is made up of 2 layers of cells. On the one hand, we have the ectoderm or epidermis (outer layer) and, on the other, the endoderm or gastrodermis (interior). In addition, they have a gelatinous substance between both parties called a mesoglea, which is especially visible in jellyfish.
• Most cnidarians have Radial symmetry: Which means that body parts are arranged around a central point. Many cnidarians have a second axis of bilateral symmetry and others only have bilateral symmetry, which implies a single cutting plane through the center.
• They are carnivorous organisms: They feed, fundamentally, crustaceans (for example, plankton), although they can also be omnivorous. Discover more carnivorous animals: examples and names in this other article.
• They have a gastrovascular cavity: It is connected to the outside by means of a mouth that is surrounded by tentacles that serve them, in part, for the capture of dams. Some cnidarians absorb organic matter dissolved directly from the water. Others, as is the case with certain types of corals, have algae that perform photosynthesis and provide them with carbon.
• Most cnidarians They present complex reproductive cycles: They include an asexual and a sexual stadium. The sexual reproduction It takes place by spawning (both males and females release their gametes to the water column, which combine generating larvae), and the asexual reproduction It is given by geming (one individual grows from another). We tell you more about asexual reproduction: what is, types and examples, here.
• They have a very variable life expectancy: There are types of polyps that live less than 10 days, while some corals in reefs can live in the same layer for more than 4,000 years. This is because they are capable of regenerating their bodies. Discover other animals that regenerate in Ecology Verde.
• They lack excrete and respiratory organs Specialized: but they do have a nervous system.
• They have some urticating cells: They are called cnidocytes, which serve both to feed and defend themselves. Inside the cnidocyte there is a capsule called cnido, which can have a lid or operculum. Within the cnido is the characteristic filament of this cell, which is rolled and folded, called nematocisto. When the Cnidocyte receives a series of stimuli (chemical or mechanical), these are processed on their surface and the operculo of the Cnido opens and the filament triggers. The cnidocytes are present in the tentacles and also in other parts of the body (as in the epidermis and in the gastrodermis). The nematocystos They contain toxic substances and serve as a defense mechanism against predators, while in other cases they have adherent substances that help them capture dams or adhere to the substrate. It should be noted that the cnidocyte filament is not reusable, so that it is only used once.
• They have a digestive cavity called Celéntero: It contains the stomach, esophagus and intestines. This cavity has an opening that acts as a mouth and anus.
• Some cnidarians are mobile and others completely sessile: Even so, most have stadiums in life in the form of a jellyfish and sessile polyp. The hydroid or sessile polyp has a more or less cylindrical shape and is subject to the substrate by the abortive face, so that the mouth and tentacles remain in the opposite part, freely exposed. Hydroid colonies are made up of different types of individuals, some dedicated to food, others specialized in defense and others in reproduction. The modus, mobile, is flattened, generally with the tentacles arranged on the margins of the body. The abortion surface of the jellyfish is up, while the oral face is oriented down.

Now that we have seen the characteristics of the Cnidarians, also called Cnidaria, we will see how they are classified. There are four types or classes of cnidarians: Hydrozoos, buckets, sciphazoos and Antozoos.

Hydrozoos (Hydrozoa class)

It includes small predatory animals that live in fresh water (hydras) or marine environments. Most generate calcite shells. Some live isolated and others in colonies. They present a non -cellular mesoglea, They lack tentacles in the gastric cavity and have no esophagus. In its vital cycles the hydroid phase predominates although, in some species, the medusoid phase is more important.

Cubzoos (Cubozoa Class)

He groups the cubomedusas, who are related to the scifomedusas but differ from these in which They are smallerthey have a primitive nervous system and eyes, in addition to a characteristic morphology in the form of a cube. Cubomedusas bites can be fatal for humans.

There is divergence of opinions as to whether they must be considered as an order or a class. When reproducing, they give rise to a polypoid state called scifistoma, relatively long lifethat can be reproduced asexually leading to other scifistomas, by forming lateral yolks.

At the end of this larval phase of Sciphystoma, the organism goes to the form of Cubomedusa, which are characterized by having four edges at the edges of the body where one or more tentacles are placed flattened base, which make up the so -called pedal. In addition to pedals, they also present Ropalios, which are conglomerates of sensory, photoreceptors and neurons that also appear in the scifomedusas.

Sciphazoos (Scyhozoa class)

It is the kind of “True jellyfish”. All their specimens live in the ocean. They have a short phase in the form of a polyp (scipopolipo or scifistoma), while most of their lives pass it in the form of a jellyfish (Escifomedusa).

They are larger size That the halves of the hydrozoos, being able to reach up to two meters in length, although it is normal to be between 2 and 40 centimeters in diameter. They are characterized by presenting a cell meshogle, as well as tentacles in its gastric cavity.

There are jellyfish in which fertilization takes place in the handlebar, where embryos develop until it gives rise to the “Larva Flanula”, which is free and,, At the end of her swimming life, she goes to the background and gives rise to scifistoma. The scifistoma is like a polyp that can live for a few months and, by geming or stroke processes, gives rise to new individuals.

Through strobilation, sciphystom generates Éfiras, small -sized records that are free in the water and develop until the form of jellyfish. The time that each phase of these cnidarium animals occupies is very variable: there are longer life scifistomas, while, in other species, it is practically non -existent and the Larva Flanula directly gives rise to an Éfira …

If you want to know more about the so -called “true jellyfish”, here you can learn how jellyfish reproduce in ecology.

Antozoos (anthozoa class)

The following cnidarium animals include:

• The anemones.
• The corals.
• The sea feathers.

Is The largest class of Cnidarians or Cnidariawith more than 6,000 known species (there are many fossil specimens) in all seas, even at great depths. They only present polyp, non -medusoid and live in marine environments.

They can live alone or in colonies. The individuals They have a column shape with an abortive end where They are subject to substrate and an oral end where the mouth surrounded by tentacles is located. In the Antozoos, the mouth continues through a pharynx that occupies a good part of the gastrovascular cavity.

In the area where the pharynx is located, the Antozoos have complete or incomplete tents or mesenterios that increase the surface of absorption and digestion. The most important Antozoa group is the Hexacoralia subclass that mainly contains the anemones and stone corals, which form the coral reef.

After this review of the types of cnidarians, we will see specific examples of each of them.

At this point in the article, you know what the Cnidarians and their characteristics are, so we now present Some examples of cnidarians indicating each class.

• Hydrozoos: Pennaria Disticha and Obelia geniculata.
• Cubozoos: sea wasp (Chironex Fleckeri), Irukandji Medusa (Carukia Barnesi), Medusa Habu (Chiropsoides quadrigatus) and small sea wasp (Tripedalia Cystophora).
• Sciphazoos: Common Medusa (Aurelia Aurita), the aguacuajada (Cotylorhiza Tuberculata), Medusa Luna or AURTITA (Aurelia Aurita) and Medusa Clavel (Pelagia Noteticula).
• Antozoos: sea tomato (Equine Actinia), Common Sea anemone (Anemonia viridis), Anemone Urticina (Feline urticina).

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