Cotylorhiza tuberculata

Mild Stinger
Harmless to humans, but it is better not to touch it. It is probably harmless also for most fishes. Just as for Rhizostoma, it is often associated to young fish that use it as a shelter. 


Habitat
Very abundant in the Mediterranean Sea, expecially in bays. In 2009 it was more frequent in the southern part of Italy, showing a preference for warmer waters, but this was not confirmed in 2010 and 2011, since this species was very frequent throughout the whole Italian coast, especially in the second half of the summer. 


How to identify it

One of the most beautiful jellyfish of the Mediterranean Sea. The umbrella can measure 30 cm in diameter, it is very rigid and roundish in its centre, where it has a reddish or yellow color. The external part of the manubrium is motile and pulsates vigorously. Under the umbrella, the manubrium resembles a bouquet of flowers, with blue-purple buttons, inserted into stout arms. Some tentacles, also terminating with blue buttons, are inserted on the manubrium.
Cotylorhiza can have symbiotic microalgae that live in its tissues, just as those of tropical corals. Functionally it is a “plant”, even if it can feed on zooplankton.

Marivagia stellata

Mild Stinger 

This species is rare so far, and there is not much information about its effects on humans, apparently it is not a stinger.

Habitat

Discovered in 2010 along the coasts of Israel by the marine scientist Bella Galil. It comes from the Red Sea, where it probably passed unobserved, and entered the Mediterranean from the Suez Canal.

How to identify it
The name of the species (stellata) describes star-like reddis spots that adorn the umbrella. It is recorded just from the Eastern most part of the Mediterranean Sea, but it might expand in other seas. If you see it, a picture is needed to confirm your record.
 

Aequorea forskalea

Mild Stinger
Not big (max 10 cm) and harmless because its cnidocysts are not dangerous for humans. 



Habitat 

Never very abundant along our shores, even though it can be in large swarms locally, especially in spring. 



How to identify it

It is a hydromedusa that buds from polyps that live on the sea bottom. It does not have a large size, reaching a max of 10 cm in diameter. It is easily distinguished from other jellyfish because it has many radial canals that link the centre and the margin of the flat bell. The mouth and the manubrium are inserted in a gelatinous bulg that originates from the centre of the bell and projects downwards. From this jellyfish genus, the green fluorescent protein (GFP) was isolated a substance that produces light in many jellyfish. The discovery of this protein allowed the development of new techinques for diagnosing pathologies and research in molecular biology. This discovery led to application in diagnostics, allowing to mark specific cell lines. The american researchers Osamu Shimomura, Martin Chalfie and Roger Tsien were awarded the 2008 Nobel prize in chemistry for their discovery of GFP.

Aurelia aurita

Mild stinger

The venom of Aurelia is harmless for humans and this jellyfish can be touched (in China it is a popular dish) even though, like all jellyfish it is very delicate and contacts can damage it.

Habitat

Aurelia lives in all oceans of the northern hemisphere, where it can be very abundant.

How to identify it

The umbrella can reach 30-40 cm, with marginal tentacles, discoidal, withish, with gonads arranged in four circles that are very evident through the transparent bell. The manubrium has four long oral arms. Many radial canals link the centre and the margin of the umbrella. Contrary to other species, this jellyfish lives well in aquaria and can be observed in the public aquaria throughout the world. 

Carybdea marsupialis

Stinger 


Carybdea marsupialis is a cubozoan, as the deadly jellyfish that inhabit Australian coasts. Luckily, its venom is not deadly: its stings are painful, but the effects last just a short while. 



Habitat 

Present in the mid and northern seas of Italy, it is increasingly more frequent along our coasts. It is attracted by light and gets near the coast during the night. 



How to identify it

Relatively small, transparent, with cubic umbrella measuring from 4 to 5 cm, it is armed with 4 long tentacles. It swims vigorously and moves quickly. Just as Pelagia, it is typical of the Mediterranean and is one of the most stinging species of our seas.

Cassiopea andromeda

Stinger 


It is not very dangerous, but it is better not to touch it because it produces mucus with dispersed stinging cells, and entering in contact with this mucus causes irritations.

Habitat
It entered the Mediterranean Sea through the Suez Canal, and is expanding through the Turkis coasts. In 2010 it was recorded at Malta, and so it reached the Italian waters. It is mostly found on sandy bottoms, but it can be present also on rocks.

How to identify it

The diamater can be 30 cm maximum, the jellyfish usually rests on the sea bottom, with the umbrella towards the bottom, whereas mouth and tentacles are upwards. For this reason, the species is called the upside down jellyfish. It has this posture because there are unicellular algae in its tissues, similar to the symbiotic algae of tropical corals, and they are also symbiotic with the jellyfish that, to make them function properly, has to expose them to light.

Catostylus tagi

Stinger 


It is not a bad stinger, but it is better not to touch it. 



Habitat 

It is common along Portuguese coast and, in general, throughout the Atlantic Ocean, but it was never recorded from the Mediterranean Sea, until Maria Ghelia photographed it in 2010, in the waters of the Pantelleria Island. 


How to identify it

It is similar to Rhyzostoma pulmo but it does not have the typical bluish-purple umbrellar margin typical of this species. It is a beautiful animal and, in some countries, it is used as food.
 

Chrysaora hysoscella

Stinger 


Its stinging properties resemble those of Pelagia, but it is a less severe stinger.

Habitat 

It lives in the Atlantic, and it can reach high latitudes, for instance Norwegian fjords, where it can be present in thick swarms. In Mediterranean it is never abundant but it is frequent. 


How to identify it

The umbrella can reach 30 cm in diameter, the manubrium (the organ hanging from the centre of the umbrella, with the mouth at its end) has four oral arms that can be even 1 m long. The upper part of the umbrella is decorated by 15 V-shaped bands that start from the centre of the umbrella and reach the margin, where there are 24 tentacles, in groups of 3. Chrysaora is a very elegant animal, perfect for being pictured.

Drymonema dalmatinum

Stinger 


A strong stinger, it might be dangerous due to its large size. 


Habitat
Heckel, the great naturalist, described it in 1880: a large jellyfish along the Dalmatian coast, in the Adriatic Sea, and he called it Drymonema dalmatinum. For many years that description was the only sign of existence of this species but in 1940 another researcher (Stiasny) found it again on the east coast of the Adriatic Sea. Then complete oblivion for this species, until when Drymonema became a pest, for some time, along the coasts of Puerto Rico. Recently, it re-appeared in Croatian coasts and it can easily reach the Italian waters. 



How to identify it

Drymonema is a very rare species, very similar to the largest jellyfish of the world, the northern Cyanea capillata with even 2 m of umbrellar diameter. Also Drymonema can reach a remarkable size: it can be even 1 m in diameter and it is the largest jellyfish of the Mediterranean Sea. How is it possible that an animal of this size can remain undetected for decades? Probably Drymonema spends long periods on the bottom of the sea, as little polyps attached to rocks. The polyps can live (just as little corals) for decades and then, all of a sudden, they can produce jellyfish. Sometimes just a few, so as to produce new polyps with sexual reproduction. But if the conditions are favorable, this jellyfish, just like all the other species, can be represented by millions of individuals.
 

Mnemiopsis leidyi

Not a Stinger 


It is a ctenophore and not a cnidarian, so it is gelatinous but it is not a stinger, simply because it does not have stinging cells. It is harmless for humans but extremely dangerous for the eggs and the larvae of fish, having the possibility of changing the functioning of ecosystems, as it did in the Black Sea, where it is a very unwelcome alien. 



Habitat 

Arrived to the Black Sea in the Eighties, transported in the ballast waters of US oil tankers, it remained confined in that basin for decades. In 2009 was recorded in great quantities throughout the Mediterranean Sea.

How to identify it

Mnemiopsis leidy is a ctenphore, a gelatinous organism a little more than 10 cm long, with an egg-shaped lobate body. It does not swim by pulsating the bell (like true jellyfish do) but it has eight ciliated bands on its body, the cilia are organized so as to form platelets called combs (hence the name comb jellies given to ctenophores) that beat with iridescent waves of action that make “flow” the apparently motionless animal through the water. The Black Sea was already in trouble due to overfishing and pollution when Mnemiopsis leidyi arrived and depleted fish populations by eating the eggs and larvae of the fish, and also the planktonic prey of the juvenile fish. Its impact on Mediterranean systems is still unknown and, anyway, the effects of their predation (the absence of adult fish) are perceived only after they have played their role (eating the eggs and larvae of the fish, before they become of commercial size).
 

Olindias phosphorica

Stinger 


Its stings are not severe, but they are painful enough to spoil your day. 


Habitat 

In past years it was very abundant along the Tunisian coast, where it caused problems to the tourist industry. In 2009 the presence of these jellyfish along our coasts was sporadic. They never form extensive swarms, but they can be locally abundant. 


How to identify it

It is a hydromedusa, just as Aequorea forskalea, but it is a stinger even if it is smaller than Aequorea, reaching 6 cm in umbrellar diameter. It buds laterally from polyps that live on the sea bottom. After a period of rest on the bottom, it pulsates vigorously towards the surface, and then falls towards the bottom again, with its tentacles extended through the water. During the sinking phase, the jellyfish catches the plankton that makes up its food. Seeing it rising from the bottom gives the impression of being attacked, but it is just an impression.
 

Pelagia noctiluca

Stinger 

This is the worst stinger of the whole Mediterranean, in terms of number of stung people. The stings can be very painful and can leave scars on the skin. The effects can persist even for a relatively long time. Most jellyfish stings in the western Mediterranean are from this species.

Habitat
In the early Eighties, Pelagia was abundant throughout the Mediterranean Sea, then it disappeared to reappear at more or less decadal intervals but, since the very hot 2003, its presence is rather constant in the western Mediterranean. In the summer, it can be present in persistent swarms that can spoil the tourist season even for months.

How to identify it

The umbrella is about 10 cm in diameter, and is armed with 8 long tentacles that, when extended, can reach also 10 m length. The mouth has four long oral arms, the color of the whole animal is mauve. Hence the name: mauve stinger. The swarms can be very thick and if they invade a cage aquaculture plant, the effect can be devastating. Since the jellyfish can eat also the eggs and larvae of fish, the impact on fish stocks, and then on fisheries, can be equally devastating. They can also enter the cooling systems of power plants, and block it.
 

Phyllorhiza punctata

Mild Stinger 

Just as Rhizostoma, it does not inflict painful stings and is not a menace for swimmers, unless the contact is very intense.

Habitat
It originates from Australia. In 2009 a specimen was seen for the first time along the Italian coast, at Tavolara Island, in Sardinia.



How to identify it
Withish or blusish, and covered with yellow spots, hence the name: the spotted jellyfish. It is placed in the same family of Rhizostoma, and can reach the size of this large jelly (even more than 50 cm of bell diameter) sharing also its general structure. It feeds on crustacean plankton and, probably, also of fish eggs and larvae. Hence it is both a predator and a competitor of fish and it can cause the impoverishment of the seas. Some years ago it formed extensive swarms along the Florida coasts, causing a sudden crash in fish populations. It is edible.

Physalia physalis

Stinger 


Stung people rarely see the animal, but they feel a very painful sting. In some cases, the encounter with Physalia can be deadly. In the summer of 2010 a woman was killed by Physalia in Sardinia, and many swimmers were sent to hospital by this dangerous stinger.

Habitat 

Physalia has been recorded from the Mediterranean Sea since ancient times, but is never frequent. In 2009 it stund several people in the Eastern Mediterranean, in Corsica, in Ligury and in Tuscany. It reappeared also in 2010 and 2011. Physalia, also known as Portuguese Man of War, does not live suspended in the water, as most gelatinous plankters, but it floats on the surface of the sea, the tentacles hanging downwards. It is not a true jellyfish but, instead, a siphonophore: a colony of polyps and medusae.

How to identify it 

Physalia has a large bladder full of gas, the pneumatophore, the float of a colony of polyps with a mouth, that digest the prey, and polyps armed with stinging cells containing a powerful venom, extremely efficent also with humans. The pneumatophore can measure 15 cm, but the extended tentacles can reach even 20 or 30 m. 


Porpita porpita

Mild Stinger
It is harmless to humans, but it is better not to touch it anyway.

Habitat
Less common than Velella in the Mediterranean Sea, it floats on the surface of the sea, just as Physalia and Velella. It can be present in swarms, but it usually less abundant and frequent than Velella. Inevitably the swarms reach the coast and strand on it, but this happens usually at the end of the life cycles, when the medusae already detached from the colonies.

How to identify it
Also known as Blue-button Jellyfish, it is not a jellyfish but a floating colony of polyps. The colony is 3-7 cm long, and the blue polyps are attached to a round chitinous float. The colonies produce small jellyfish that probably then give rise to a series of stages that resemble those of Velella.
 

Rhizostoma pulmo

Mild Stinger 


The tentacles are short and are armed with cnidocysts that are not very painful, but they can cause mild rashes if touched with insistence.

Habitat 

It is abundant along our coasts. These large jellyfish, often present in great quantities, can become microcosms that are used by other organisms: they are often a shelter for juvenile fish and small crabs can find a refuge among their oral arms.

How to identify it
It is the largest Mediterranean jellyfish (after the rare Drymonema): the umbrella can reach a diameter of 60 cm and it weight 10 kg. The color is white, with a blue umbrellar margin. The manubrium is large and it looks like a white cauliflower. It does not have a single mouth but many small mouths instead. 
It is an imposing animal, moving with slow and powerful pulsations. It is a delicacy for several oriental people.

Rhopilema nomadica

Stinger
A bad stinger, it can be confused with the almost harmless Rhizostoma from which it can be distinguished due to the characteristic blue rim of Rhizostoma.

Habitat
The genus Rhopilema is typical of the Indo-Pacific ocean and has no Atlantic or Mediterranean representatives. It never reached the Italian seas, possibly because the temperatures are not high enough for this tropical species. In the Eighties this species became suddenly abundant along the Israeli coasts of the Mediterranean Sea: it probably reached the Mediterranean from the Red Sea, through the Suez Canal, hence the specific name “nomadica”. In the eastern Mediterranean it causes great harm to tourism, fisheries, and industry.



How to identify it

It does not pass unnoticed, since it can reach 80 cm in diameter and can form extensive swarms. The current global warming might pave its way towards the expansion of this species in the Western Mediterranean.

Thalia democratica

Not a Stinger 

It is a thaliacean, and so it is a herbivorous gelatinous plankter that filters the water through its mucus-laden gills, that trap phytoplankton and bacteria. Salps have neither cnidocysts nor colloblasts and, thus, are harmless to humans, but their massive presence can impoverish the sea by removing primary producers (the phytoplankton). 



Habitat 

Thalia form extensive swarms that usually thrive offshore.

How to identify it

Thalia democratica derives its name from its ability of forming long chains of barrell-shaped zooids, with an evident orange spot that is evident through the transparent body. Salp chains can reach 6 m. The massive presences of this species are sudden and can last just a few days.
 

Velella velella

Mild Stinger 


It is harmless to humans, but it is better not to touch it anyway. 



Habitat 

Common in the Mediterranean Sea, it floats on the surface of the sea, just as Physalia. It can be present in enormous swarms, several km long. Inevitably the swarms reach the coast and strand on it, but this happens usually at the end of the life cycles, when the medusa already detached from the colonies. 


How to identify it

Also known as the By-the-wind sailor, it is not a jellyfish but a floating colony of polyps. The colony is 3-7 cm long, and the blue polyps are attached to a chitinous float with a “sail” that makes the animal travel by using wind energy. The colonies produce small jellyfish that sink, reproduce sexually giving rise to the conaria stage that then transforms in a series of stages that, from the deep sea, reach the surface and become the new colonies.