Most of us have come across this curious animal on some occasion and, perhaps, you have been unlucky enough to suffer its painful stings or lucky enough to have seen this spectacular animal free in the ocean.
Have you ever wondered how these animals are raised? Interestingly, jellyfishreproduction does not take place inside the female as it does in mammals. If you want to discover how it is produced, don't hesitate, keep reading this article on our site.
Characteristics of jellyfish
Jellyfish belong to the "Cnidaria" Phylum, which encompasses some 10,000 species, of which only 20 are freshwater, since the rest are marine. They have primary radial symmetry (the division of an animal into similar halves along the longitudinal axis of the body) in many secondarily modified to biradial or even bilateral (a single plane divides the animal in two halves, left and right).
Its body is organized as a blind sac with a single hole for the entry of food and exit of waste, with a digestive cavity called the "gastrovascular cavity", gastrocele or coelenteron, and works by digesting food and sending nutrients and oxygen to the rest of the body.
The pole opposite the mouth is shaped like a bell or umbrella, constituting the umbrella characteristic of these animals. They stand out for having highly developed sense organs, located on the edge of the umbrella. We find visual organs (ocelli) and static organs (statocysts), which serve to maintain balance. Jellyfish can be predatory or suspensivorous (filtering the water around them, thereby trapping small food particles).
They also have specialized cells known as "cnidocytes". There are several types, but the most common is the nematocyst, which is stinging, with hunting and defense functions. The nematocyst is present in its tentacles and through it it provokes the stings. Another important type is the pticocysts, they secrete a mucus that serves to capture small animals or nutritious particles.
Another very important characteristic of this group of animals is that they have two body forms: the form polyp, which is generally benthic (lives anchored to the seabed) and often colonial (live in large groups of individuals) and the form medusa, planktonic (lives floating in the water) and usually solitary. There are species that only have the polyp form, others only jellyfish and others that have both forms in their life cycle.
How is jellyfish feeding?
Jellyfish, due to their planktonic lifestyle, are predatory animals In their tentacles we find nematocysts, cells that have an internal capsule (cnidocyst) filled with the stinging liquid and a filament It is fired by a cilia (cnidocilium) sensitive to contact.
When a fish gets too close to a jellyfish and lightly brushes against one of its tentacles, these nematocysts are activated, they are expelled from their capsules and inserted under the skin of the prey, immobilizing it. Once the prey cannot move, with the help of the tentacles, it moves it towards the mouth and, from there, it passes into the digestive cavity.
The reproduction of jellyfish and polyps
To understand the reproduction of these animals we must first know where the jellyfish live. All cnidarian species live in the aquatic environment, either s alt or fresh water. In this type of environment, internal fertilization (the union of the egg and the sperm occurs inside the female) is not common, so cnidarians have external fertilizationFemales and males release eggs and sperm to the exterior, respectively. In hermaphroditic species, an individual will release both eggs and sperm.
As we said earlier in the article, there are species that only have the polyp form, species with the medusa form and species with both forms. Most of them are hermaphrodites Other species are dioecious and have separate sexes. Thus, the polyp-shaped species release the gametes into the environment, producing fertilization afterwards, giving rise to a larva, which will live free until it adheres to the seabed in the form, again, of a polyp.
When a species has both forms in its life cycle, the polyps by strobilation (a type of asexual reproduction) produce jellyfish, these when they grow, release the gametes that, as in the previous case, are they fertilize producing a larva that will end up forming a polyp and this, by budding, will give rise to a whole colony of polyps.
In other cases, the egg formed by the gametes released by the jellyfish does not give rise to a larva that will end up forming a polyp, Instead, a jellyfish emerges directly from the egg, so the polyp phase is inhibited.
Jellyfish Curiosities
As you may have seen, reproduction in jellyfish is, without a doubt, spectacular. This group of animals is full of surprises. For example, it is the only group capable of forming macroscopic geological structures visible from space: the coral reefs (Order Scleractinia).
They are made up of 95% water and only 5% solid materials, for this reason they are commonly known as " aguamalas" or "aguavivas".
There is a kind of jellyfish, the Turritopsis Nutricula, which is one of the animals that live the longest and which we could call immortal, since that when it reaches its adult phase of "medusa" it is capable of reverting to a polyp, being able to repeat this process infinite times.
