Jellyfish: what are they and what types are there?

brown jellyfish

There are many types of jellyfish in the Mediterranean, depending on the class we are talking about its sting can be more or less dangerous. In recent years, the population of this gelatinous animal has increased substantially, causing serious problems for marine ecosystems and the environment.

According to experts, it is considered that the main reason for the increase in jellyfish is the decrease in the number of their predators (mainly turtles) due to overfishing, pollution and warming of the seas. In this article we explain the most abundant types of jellyfish in Spain and the consequences of their stings.

What are jellyfish?

What are jellyfish?

They are invertebrate animals that belong to the group of cnidarians (knidé = nettle, from the Greek). The Cnidarian group is classified into the following four classes:

  • Hydrozoa: Hydra, small jellyfish and other colonies of polyps.
  • Cubozoa: Box jellyfish.
  • Scyphozoa: Big jellyfish. It is the class that we mainly recognize as jellyfish.
  • Anthozoans: Anemones and corals.

They have stinging cells called cnidocytes, and use them to defend themselves and hunt prey. Cnidocytes are very sensitive. They are in a capsule that has a coiled filament, like a fishing line, and the poison inside. When the prey touches the surface of the jellyfish, the capsule opens and the filaments come out and stick to the prey, where the venom is injected. Unfortunately, sometimes it is activated by our touch, although we are not even remotely the target of the jellyfish.

Jellyfish are also called aguamalas or aguaviva. And they are pelagic animals, that is, they live in the open sea. One of their peculiarities is that they are dragged by sea currents, although they can be propelled to change direction a little, thanks to their umbrella.

They are radially symmetrical animals, being 95% of your body composition water, and its main parts are:

  • Umbrella
  • Manubrium (or tentacles or oral arms). They are the tentacles that surround the mouth and help it to feed.
  • Stinging tentacles. They are the most external and the ones they use to defend themselves and hunt.
  • Gastrovascular cavity. Internal cavity with a single opening that acts as both anus and mouth, where digestion takes place.

But how do jellyfish eat and reproduce?

But how do jellyfish eat and reproduce?

They are carnivorous and can grow rapidly and congregate in large numbers when food is plentiful. But if food is scarce, they can shrink back. These little ones that remind us a bit of that viscous mass from the movie Flubber, have an anatomy that is not at all complex. You can even see through its transparent body its last prey before being digested. They feed mainly on zooplankton, small crustaceans and some minnows.

The reproduction of jellyfish is the most curious. Jellyfish as such have male and female individuals, having a sexual reproduction, by releasing sperm and eggs into the water. This union gives rise to planula, which are the larvae of jellyfish. The planulae take root in the marine substratum and form polyps. The polyps by asexual reproduction, give fruit to a multitude of mini jellyfish called ephyras, which with the passage of time and nurturing will grow. Their name is due to the fact that they are ephemeral, since this phase lasts a very short time.

What are the natural predators of jellyfish?

Moon fish

Today the jellyfish predators that are known are:

  • Sunfish (Mola mola)
  • Sea turtles, especially the leatherback sea turtle (Dermochelys coriacea)
  • Sea birdssuch as fulmars (Fulmarus)
  • Whale shark (Rhincodon typus)
  • some ccrabs, like the arrow (Stenorhynchus seticornis) and the hermits (Paguroidea)
  • Some Whales, such as the humpback or hunchback (Megaptera novaeangliae)
  • Other cnidarians like anemones (actinaria)
  • Some nudibranchs (nudibranch) or sea slugs, which use the jellyfish's stinging cells to defend themselves against other predators!

Most common jellyfish on the Spanish coast

sure you have seen brown jellyfish occasionally on the beach, but What are they called? Is their bite worrying? As we know that all these doubts assail you, especially on summer days, we are going to give you a list and information of the most common jellyfish in Spain. First we are going to list the jellyfish as such, that is, those that belong to the scyphozoan class:

Cotylorhiza tuberculata

Cotylorhiza tuberculata

  • belongs to the order Rhizostomeaespecifically to the family Cepheidae. They are also commonly called aguacuajada, fried egg jellyfish or curly acalefo.
  • They are characterized because they are yellowish brown jellyfish, with a greenish touch due to some symbiotic algae that they have inside and a protuberance in the middle of a brownish orange color, and its umbrella is flattened. Due to its morphology, that is why it is known as a fried egg.
  • They are one size 20 to 25 cm in diameter, 8 oral arms covered with a kind of mini tentacles with white or bluish buttons. And its umbrella is divided into 16 lobes, subdivided at once into more than a hundred. On the edges of their umbrella they do not have tentacles.
  • They are pelagic, inhabiting both the open sea and the coast. Although there are usually more on the coast where their polyps can take root. It is quite common to see them in the Mar Menor, and in the Mediterranean during summer and autumn.. In winter they are rather in the form of polyps
  • The danger of its sting is low, in part because their tentacles are very short and because they barely have cnidocytes (urticate cells). So do not worry if it stings you, its effects are very mild and it does not usually cause anything more than skin irritation and hives. However, in some exceptional cases an allergic reaction could occur.

Aurelia aurita

Aurelia aurita

  • belongs to the order Semaeostomeae, Family ulmaridae. It is commonly called as jellyfish moon. It is the form that we best identify as a jellyfish.
  • They can measure up to 25 cm in diameter.
  • They have the umbrella in dish shape, and the arms from his mouth are scalloped (wavy) and much longer than the short tentacles at the edge of its umbrella. From their appearance, it is characteristic that if you look at them from above they have a kind of purple-violet "flower with four petals", which are their reproductive organs and their general color is transparent stained with a whitish blue.
  • They usually live in shallow waters, in lagoons and coastal areas, their development being better in brackish waters.
  • They are not usually seen much on the Spanish coasts, they are particularly seen in coastal areas and lagoons such as the Mar Menor, fjords and closed bays where inland water enters.
  • As for its danger, it is very low..

Pelagia noctiluca

Pelagia noctiluca

  • belonging to the order semacostomeae, Family Pelagiidand, they are known as luminescent jellyfish.
  • They can measure more than 20 cm in diameter. Its umbrella has a hemispherical shape, rather flattened, with four long, scalloped, well-stout oral tentacles. At the edge of their umbrella they have 16 tentacles that when they are deployed they can reach up to more than 20 meters in length!. Something characteristic of these beautiful but highly stinging creatures is that they have the entire surface (oral arms, tentacles and including the umbrella) of Warts where cnidocytes accumulate. They have a reddish pink color, which makes them quite striking.
  • They are pelagic and do not have a polyp phase like other jellyfish. As they live in the open sea, it is where large schools of these individuals are usually seen. Being their periods of reproduction in spring and autumn, so these will be the times in which more individuals are seen.
  • They usually live in the open sea, and if they reach the coast it is because the storms drag them to the coast, are usually quite common in summer. And they can be seen in both the Atlantic Ocean and the Mediterranean Sea.
  • As for the its danger is very high. produce a lot of irritation and itching, they can even cause wounds that can become infected. As they have such long tentacles they can affect a considerable surface of the skin, this implies that the effect of the poison it can even cause respiratory, cardiovascular and dermatological problems that can last for weeks or even months. So be very careful with these jellyfish!

Rhizostoma pulmo

Rhizostoma pulmo

  • They belong to the order Rhizostomeae, Family Rhizostomatidae. They are also called aguamala, aguaviva or blue acalefo.
  • Regarding its size, They are the largest we can find, with a diameter that can reach 90 and 100 cm. The umbrella has bell-shaped, bluish-white in color and with many lobes on the edge of the umbrella, violet in color, in addition to tentacles on its edge. Have 8 oral tentacles fused into a bluish-white manubrium. And this in turn forms a scalloped crown with 16 points, from which 8 bluish little arms come out that end in the shape of a club.
  • They can be found both in open and shallow waters, although they are rather coastal because they need a substrate for their polyps, and because it is thought that among the jellyfish they are the ones that have the greatest ability to move when going to regions where there is more amount of food.
  • It is a native species of the Atlantic Ocean and the Mediterranean Sea. So they can be seen from late spring to fall. You may see them both alone and in banks. And in winter, they are in the form of a polyp in the shallow waters.
  • They are not as dangerous as Pelagia noctiluca, we would still classify its dangerousness as medium. It is curious because they do not produce serious dermatological conditions. However they can produce irritations only with its presence in coastal waters closed to the open sea, it is not even necessary to have direct contact with the jellyfish or any fragment of its body.

Other jellyfish, which are not officially jellyfish

Yes, we clarify this title, they do not belong to class Esciphozoan, therefore, officially they are not jellyfish. However, to our eyes because of their appearance, they can pass as jellyfish. We mention which are the most common on the Spanish coasts:

Velella Velella

Velella Velella

belonging to the class hydrozoo, bluish color, it is shaped like a disc with a “weather vane” on top. They are tiny of 1 to 8 cm. And although it looks like a jellyfish it's a floating colony of polyps! They usually go in banks and it is more common in spring and early summer. Regarding its danger, it has none.

Aequorea forskalea

Aequorea forskalea

belonging to the class hydrozooThey are like jellyfish and with a flattened, transparent umbrella that can measure up to 30 cm. On the edge of the umbrella it has numerous very fine filaments that allow them to eat. Its habitat is usually Atlantic Ocean, although it rarely occurs in the Mediterranean. However, as the climatic conditions are changing, it is beginning to be observed on the coasts of Catalonia and the Balearic Islands. Regarding its danger, they are totally harmless.

Carybdea marsupialis

Carybdea marsupialis

belonging to the class cubozoo, they are cube-shaped with four tentacles, one at each corner. They are small in size, measuring between 5-6cm diameter. Transparent in color that turns between blue and white. They usually live in deep waters, although sometimes due to water currents they can be seen on the surface, so it is difficult to see them on the coast, and thank goodness, because its danger is very high.

Physalia physalis

Physalia physalis

Also called Portuguese caravel. belongs to the class hydrozoo, forms a polyp colony, where one of them has the form of "float", which is the one that is mainly seen and measures between 30 long and 10 cm wide. For its size, it has very long tentacles and many are loaded with nematocytes, which makes it highly dangerous.

In fact, the simple touch with any of its tentacles can bring you serious consequences such as a neurogenic shock as a result of intense pain, as well as burning, severe pain and skin injuries. It usually lives in the warm waters of the Atlantic Ocean, although it has occasionally been observed in the Mediterranean.

Here we leave you the link of a app that warns you about jellyfish sightings in your area, so you can go to the beach with more peace of mind this summer. I hope this information has been useful to you.


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