There are more than 4,000 species of jellyfish. And every year, their proliferation is increasing. What is the reason for this spread? Every summer, thousands of jellyfish arrive on our Mediterranean coasts, mainly due to the increase in ocean temperatures. Given this growing trend, we thought it would be interesting to discuss how jellyfish reproduce. And the truth is that they have a very interesting life cycle Do you want to know more?

How do jellyfish reproduce?

Jellyfish, among other things, are unique in that they have a life cycle that is unusual in the animal kingdom. These marine animals belong to a class of fauna known as hydrozoa. This family is characterized by an alternation of generations. That is, a sexual generation is followed by an asexual one.

Do jellyfish have gender?

Yes, jellyfish have a gender, and are recognized asdioecious species . The spermatozoa of the male fertilize the eggs of the female, forming the zygote. This will grow as a larva (or planula), as occurs in mammals, birds and fish. These planulae begin their free life, until they attach to the seabed and grow to form a polyp, which for a time will only be responsible for taking food. When the colony of polyps reaches an optimal state of nutrition, it begins the process of division by means of transversal grooves to reach a later formation of individual jellyfish.

These small discs develop into free-living larvae, which grow and transform into an adult jellyfish with gonads in which the eggs or sperm will form.

To understand the reproduction process of these gelatinous animals, we must know where they live. All species of cnidarians live in the aquatic environment, whether saltwater or freshwater. In this type of environment, internal fertilization (union of the egg and sperm occurs inside the female) is not common, so cnidarians have external fertilization. Females and males release eggs and sperm to the outside.

There are also hermaphrodite jellyfish species. In this case, they will release both eggs and spermatozoa indistinctly.

Types of jellyfish reproduction

As we mentioned at the beginning of the article, jellyfish reproduction is differentiated, depending on the species, into sexual and/or asexual. Below, we summarize each of the processes.

On the other hand, in the sexual reproduction of jellyfish, species of different sexes release their gametes for fertilization to occur. They usually do so at the same time of day, under certain light conditions and close together, so that there is a greater chance that, with so many sperm and eggs, they will not meet by pure misfortune. It is a strategy similar to that used by their cousins the corals, as well as other much more "modern" animals, such as fish.

The asexual reproduction of living waters is one in which the polyp reproduces asexually. Depending on the species, the division changes. This process is known as strobilation. We may be surprised by the fact that some species of jellyfish are hermaphrodites, whereby the same specimen can bathe between its own eggs and sperm, fertilizing itself. But a few species do something much more striking.

Some jellyfish reproduce by "oral sex".

Instead of being fertilized externally, the spermatozoa of these jellyfish travel to the "mouth" of the female, enter it and fertilize the eggs inside. The eggs will develop inside until the larvae are born and even a little longer. Other species, such as the common jellyfish(Aurelia aurita) protect their eggs in their tentacles. These tentacles form cavities that widen after the larvae hatch to shelter them for a while. As you can see, it is not very simple. And we have only just begun, because the larva has yet to develop into a polyp.

Other jellyfish curiosities

Now that you know how jellyfish reproduce, stay tuned. You are about to discover the universe of singularities that define the longest-lived animal on Earth. In addition to their characteristic reproductive system, jellyfish stand out for their many other peculiarities:

Jellyfish are 95% water.

They have no bone structure. They are soft and delicate, so they can be easily damaged. They require even more water to move and if they do not remain in their aquatic habitat, they collapse and die.

They are radially symmetrical animals

These beings are symmetrical because of a central axis that runs through the length of their body. They have an upper and lower part, but no left or right sides. They are different from other types of animals (such as mammals, reptiles, fish, birds and arthropods) which exhibit bilateral symmetry.

Your mouth also functions as an intestine

Their digestive system is extremely rustic, with a single, simple opening. These animals ingest food through their mouth, located in the lower part of their bell. The food is digested in a sac-like structure (called the coelenteron or gastrovascular cavity). Waste material is also expelled through the mouth. This cavity then functions in two ways: as a stomach and as an intestine.

They move like jets

A common analogy used to describe how jellyfish move in water is the one that refers to their movement as "a simple form of jet propulsion". It takes in water inside its muscular bell and subsequently squirts it out, creating a jet of water that propels it forward. It also takes advantage of water currents to move.

Some species produce light

Despite having a very advanced anatomy, some jellyfish are able to emit light to attract prey or when they are in danger. They have a light protein on the back of their body; some use it to defend themselves and others to attack. The jellyfish Pelagia Noctiluca is the best known for its luminescent qualities. It inhabits all oceans, but tends to be found mainly in the Mediterranean Sea.

They have 24 eyes around their body

They are almost as advanced as those of humans. While we have one pair of multipurpose eyes that detect color, shape, size and light intensity, cube jellyfish have four types of eyes with different purposes. The most primitive ones basically function as light/dark detectors to guide their navigation, and are the ones that all other jellyfish have. The two most advanced ones detect shape and serve to keep them within the safe territory provided by the underwater vegetation. The rest of the primitive eyes have them around the body as if forming a belt.

Jellyfish have no respiratory system

Oxygen diffusion occurs at the tissue level. They also do not have a circulatory or excretory system.

Its body is made up of three layers

The very strange body of every jellyfish has only 3 layers. The outer layer is called the epidermis and the inner layer is called the gastrodermis. In between, there is a thick substance called mesoglea.

They live in both salt and fresh water.

The species CraspedacustaSowerbyi is the only species of freshwater jellyfish.

Its tentacles are made up of thousands of stinging cells.

There are thousands of nematocysts in their tentacles, arms and mouth. Nematocysts consist of a capsule containing a stinger, a venom sac and chemo-sensitive hairs that allow them to detect food. When a potential prey touches these hairs, the nematocysts expel and inject the venom into the victim. The venom immobilizes the prey and the jellyfish uses its arms to pull the prey into its mouth.

Did you know that you can avoid jellyfish stings?

You can now cross "understanding how jellyfish reproduce" off your bucket list and move on to the next starting level: discovering "out of the blue" that jellyfish stings will no longer be a threat to your summer vacation. Our sunscreens also act as a jellyfish cream. They protect the skin in contact with jellyfish and prevent their sting. If you have ever been stung by a jellyfish and do not want to live such an unpleasant experience again, we encourage you to take a look and share with your loved ones our anti jellyfish sunscreens for babies, children, adults and athletes.

I'm sure you will find them very useful :)

Thanks for reading us! See you in the next post.