The coelenterates are animals invertebrates eumetazoan diploblastic, having radial symmetry and its body has a unique gastrovascular cavity. This cavity communicates with the outside through an orifice that works as a mouth and anus at the same time.
Despite the fact that the term coelenterated is not part of the dictionary of the DigoPaul, its use is increasingly frequent and, possibly, with the passage of time, it will also end up being accepted by those who regulate the rules of our language. It should be noted that this concept derives from the word coelenterate that comes from a Greek word that means “hollow intestine. ”
The coelenterates formed a phylum of animals that included the cnidarians and the ctenophores. At present it is not clear whether these groups are directly related, so they are studied separately.
Cnidarians have special cells called cnidoblasts or cnidocytes, which allow them to secrete an stinging substance to attack their prey or defend themselves against predators; an example of this group are living waters and sea anemones. Ctenophores, on the other hand, have sticky clobastos that fulfill the same function.
In the case of cnidarians, which are divided into some 10,000 species and live in different aquatic environments, it is possible to distinguish between polyps (which are fixed and have a sac-like shape, with an opening upwards) and jellyfish (with the capacity to movement in water). Ctenophores, which are exclusively marine, have a single form in their about 100 species.
Body structure and functionalities of the organism
All coelenterates have a single hole that serves both for the entry of food and for the elimination of residues that come from digestion, which is why they are said to have an incomplete digestive system. In addition, almost all of them have a series of tentacles around their mouths that allow them to capture food and defend themselves from their enemies.
Regarding their body structure, they have an outer layer (epidermal) whose purpose is to protect them from harmful agents and interact with the environment, an internal one (gastrodermis) that serves them to carry out digestion that is done intracellularly. In addition, between the two layers they have a gelatinous structure (mesoglea) which is what supports them and facilitates their movement. The mesoglea is connected to the epidermis through nerve cells, allowing everything that they perceive with their external skin to be captured by the whole organism and can respond according to the sensations that are transmitted through the neuro-motor sensory mechanism.
Unlike other animals belonging to the invertebrate group, coelenterates lack a circulatory, respiratory and excretory system, in such a way that food must be distributed through the gastrovascular cavity, gas exchange is carried out by diffusion and excretions they are also released through the broadcast system. Regarding their habitat, they are aquatic animals, most of them marine, although there are also freshwater ones.
Regarding reproduction, cnidarians comply with the alternation of generations, something that ctenophores do not. Polyps usually reproduce asexually (by sprouting), while jellyfish are divided into males (which produce sperm) and females (which produce eggs). It is worth mentioning that there are some species that have life cycles with alternation, some generations sexed and others asexual, so that they remain in balance with the environment. At this point it is important to stop, as this element is one of the most remarkable of many species; if their predators disappeared, they would not overpopulate because they have a reproduction mechanism that contemplates the balance of the environment.