PELAGIA NOCTILUCA: CHARACTERISTICS, HABITAT, REPRODUCTION - BIOLOGY - 2025

The Pelagia noctiluca is a jellyfish belonging to the class Scyphozoa presents bioluminescence and is widely distributed in the coast of the Atlantic Ocean and the Mediterranean Sea.

Likewise, it is among the jellyfish that have the ability to swim, although this is somewhat limited. However, thanks to a rudimentary muscular system it is able to move vertically and horizontally.

Pelagia noctiluca. Source: Mark Norman / Museum Victoria

On occasions numerous specimens of Pelagia noctiluca have invaded the shores of the beaches, constituting real pests and hindering their enjoyment. This is a phenomenon that is still being studied by specialists in the area, mainly to elucidate its causes and thus be able to prevent it.

Taxonomy

The taxonomic classification of Pelagia noctiluca is as follows:

- Domain: Eukarya.

- Animalia Kingdom.

- Phylum: Cnidaria.

- Subphylum: Medusozoa.

- Class: Scyphozoa.

- Order: Semaeostomeae.

- Family: Pelagiidae.

- Genus: Pelagia.

- Species: Pelagia noctiluca.

characteristics

Pelagia noctiluca is a eukaryotic and multicellular organism. This means that it is made up of different types of cells, specialized in various functions and whose DNA is delimited by a membrane within the cell nucleus.

Likewise, this jellyfish, like most of the members of the phylum cnidaria, presents radial symmetry. According to this, all the structures that comprise it are arranged around a central axis. Furthermore, during its embryonic development, only two germ layers appear: endoderm and ectoderm. Because of this, it belongs to the category of diblastic animals.

Likewise, Pelagia noctiluca is a highly toxic animal, since its cnidocytes synthesize a toxin that can cause serious damage on contact with its tentacles. It is the cause of most cases of jellyfish stings on the Mediterranean coast.

In terms of the life cycle, this jellyfish is an exception within the Scyphozoa class. While most have a metagenetic life cycle, with a polyp and a jellyfish phase, Pelagia noctiluca has a hypogenetic life cycle, in which only the jellyfish phase appears.

Morphology

This species has the same morphology as most jellyfish. They have an umbrella, from which some tentacles come out. The characteristic shape of this jellyfish is a mushroom.

The body of this jellyfish is translucent, but not transparent. It is also characterized by having a pink color, and on the upper surface of the umbrela there are a kind of spots of a violet color. The surface of the umbrella has roughness in each spot that protrudes a few millimeters.

Likewise, on the underside of the umbrella there is a tubular extension called the manubrium. At the end of the handlebar there is a hole that is the mouth.

Similarly, long structures called oral arms are detached from the manubrium. These in turn contain small extensions of scalloped edge. The oral arms are also covered by the same roughness as the umbrela.

Specimen of Pelagia noctiluca. Observe its purple color and the spots on the umbrella. Source: Pillon, Roberto

Like most jellyfish, Pelagia noctiluca has tentacles that detach from the umbrella. These tentacles are thin and shaped like filaments. They are very long. They can even measure up to more than 1 meter in length. They generally have a total of 8 tentacles.

Similarly, the mouth opens to a gastric space or stomach, which is made up of approximately 16 radial channels.

One of the most outstanding characteristics of these jellyfish is that they have bioluminescence, that is, they can emit a certain glow in the dark. This is because in its genome there is the gene that codes for the expression of a protein called green fluorescent protein.

Digestive system

The digestive system of Pelagia noctuca is quite simple, as is the case with all cnidarians.

It is made up of an opening (mouth) that fulfills a double function: it allows the entry of food and the exit of waste products after the digestive process.

The gastric cavity is divided by four septa. Digestion takes place thanks to the digestive enzymes that are produced there in that primitive stomach. These attack the ingested prey and process them, transforming them into simpler substances to be assimilated.

Reproductive system

Jellyfish of this species are dioecious. This means that female individuals and male individuals are present.

The gonads are located in the wall of the gastrovascular cavity, which is why they are called endodermal. This is where gametes are produced. Immediately below the gonads are the so-called subgenital bags, which open to the outside thanks to a small hole that is located on the underside of the umbrela.

Through this hole the gametes are released so that the reproductive process begins.

Nervous system

The nervous system is rudimentary. It does not present specialized organs at a functional level such as a brain.

This species of jellyfish has a large number of neurons distributed throughout its anatomy, forming a kind of nerve network that allows the jellyfish to interact with its environment.

Likewise, this jellyfish has sensory organs called ropalios, which contain some receptors such as statocysts, which allow the jellyfish to orient itself in the environment and maintain balance.

The clothes are located on the lower edge of the umbrella. Unlike other species of jellyfish belonging to the Scyphozoa class, Pelagia noctiluca does not have ocelli on the clothing. This means that it lacks visual type receptors.

Habitat and distribution

The Pelagia noctiluca is a jellyfish that requires a marine environment in order to develop. It is found mainly in the waters of the Atlantic Ocean and the Mediterranean Sea.

Likewise, this is a jellyfish that prefers pelagic-type habitats. In other words, it is mainly located in those areas that are not above the continental shelves. Because of this, it is rare to see it in areas near the coast.

Regarding the temperatures it requires, this species of jellyfish is located in high temperature waters, that is, hot and temperate. It is important to note that the increase in temperatures in the waters in which it is found has an effect on its reproductive cycle: it accelerates it.

Reproduction

Pelagia noctiluca only reproduces sexually. This type of reproduction involves the fusion of sexual, male and female gametes.

Likewise, the reproductive cycle of these jellyfish differs from the cycles of the rest of the jellyfish in that it does not include a polyp phase.

Likewise, the fertilization of this species of jellyfish is external, that is, it occurs outside the body of the female.

When the ideal moment for reproduction to occur, especially when the water temperature is adequate, the female and male specimens release the gametes into the water. There they meet and merge, taking place the process of fertilization. From this menara an egg is formed, from which a small microscopic larva will develop.

Later, the larva grows and transforms into a small jellyfish called an ephira. This is circular in shape and has eight lobes. Finally, the ephira develops, increases in size and transforms into an adult jellyfish, already capable of reproduction.

Feeding

Pelagia noctiluca is a carnivorous heterotrophic organism that feeds mainly on small marine animals such as some fish, mollusks and crustaceans. If the opportunity presents itself, it can even feed on other small jellyfish.

For the feeding process, the tentacles play an important role, since they immobilize the prey and inoculate it with the toxin, which kills it.

Later, with the help of the oral arms, the prey is brought to the mouth and ingested. In the gastrovascular cavity it undergoes the action of digestive enzymes and is digested. Finally, the fragments that were not digested are released as waste through the mouth.

Bite

The stinging cells that Pelagia noctiluca possesses synthesize and secrete a toxic substance that has a highly harmful effect on the tissues of animals that come into contact with it.

The specific effect of this toxin is hemolytic and cytolytic. This implies that it is capable of destroying red blood cells, as well as any other cells with which it comes in contact. Similarly, various studies have determined that the Pelagia noctiluca toxin interferes with the proper functioning of the ion channels of the cell membrane.

Likewise, the severity of the Pelagia noctiluca bite will depend on several factors, including the time of contact with the tentacles and the amount of skin exposed to that contact.

In this sense, there are people who have only reported some local reaction such as redness, hives and irritation.

Sting symptoms

In general, the signs and symptoms of a Pelagia noctiluca bite are the following:

- Intense pain.

- Unbearable itching.

- Edema of the affected area.

- Urticarial hives. The wheal is defined as a raised lesion that has reddish edges.

- Ulceration and even necrosis (in extreme cases).

Now, if the jellyfish sting is severe, in a short period of time other systemic signs and symptoms begin to appear, such as:

- Severe headache.

- Trouble breathing.

- Spasms or pain in the muscles.

- Gastrointestinal symptoms: vomiting and nausea.

- Neurological signs: disorientation and drowsiness.

First aid in case of sting

Immediately after a Pelagia noctiluca bite has occurred, it is necessary to implement certain first aid measures that can help to alleviate the stinging effects of the toxin.

These measures include:

- Tear off the visible tentacles. Preferably with tweezers, avoid touching them directly.

- Rinse the affected site with hot water. If possible at a temperature of more than 40 ° C.

- Wash the affected area with sea water. Avoid completely washing it with fresh water.

- Avoid rubbing with sand or with anything else that may cause more irritation.

- You can apply a hydrocortisone cream and an analgesic to help mitigate the itching and pain caused by the bite.

References

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3. Halstead BW. (1988) Posisonus and venemous marine animals of the World. New York, Darwin Press. p. 4-9.
4. Hickman, CP, Roberts, LS, Larson, A., Ober, WC, & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). McGraw-Hill.
5. Morabito, R., Costa, R., Rizzo, V., Remigante, A., Nofzinger, C., La Spada, G., Marino, A. and Paulmichi, M. (2017). Crude venom from nematocysts of Pelagia noctiluca (Cnidaria: Scyphozoa) elicits a sodium conductance in the plasma membrane of mammalian cells. Scientific reports. 7.
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