The Mediterranean Sea is home to a wide variety of jellyfish and jellyfish-like drifting animals. True jellyfish belong to the phylum Cnidaria and carry specialized stinging cells called cnidocytes, which can inject venom to catch prey or defend themselves. Some Mediterranean species cause only mild irritation, while others can trigger intense pain and strong skin reactions.
Below you’ll find a practical guide to 20 well-known Mediterranean jellyfish (and close look-alikes), including appearance, where they’re commonly seen, and how risky their sting can be for people.
At-a-Glance: Sting Risk Categories
Low risk
Usually mild irritation or barely noticeable stings, though sensitive individuals may still react.
Moderate risk
Painful welts and burning are possible; symptoms often last hours to days.
High risk
Strong pain and significant skin reactions are common; medical evaluation may be needed.
1) Compass Jellyfish (Chrysaora hysoscella)
Easy to recognize by its pale bell with brown radial markings that resemble a compass rose. The bell can reach around 30 cm, while the tentacles may extend several meters.
Where you may see it
Mostly offshore, but currents and tides can push it close to beaches.
Sting risk
Moderate—often causes burning and raised welts that may take time to fully fade.
2) Moon Jellyfish (Aurelia aurita)
A translucent jellyfish with a faint bluish-white tint and four visible circles under the bell (its gonads). Up to about 25 cm wide.
Where you may see it
More often near coasts than in open water.
Sting risk
Low—many people barely feel the sting, though mild irritation can happen.
3) Mediterranean Box Jellyfish (Carybdea marsupialis)
A small box jellyfish (cubomedusa) with a square bell only a few centimeters across and four long tentacles that can reach around 30 cm. Often appears almost transparent.
Where you may see it
Prefers deeper waters (often around 20 m), so it is less common right at the shoreline.
Sting risk
High—can be very painful and leave pronounced skin lesions.
4) Portuguese Man o’ War (Physalia physalis)
Not a true jellyfish, but a colonial hydrozoan. It floats with a gas-filled “sail” (pneumatophore) and trails very long tentacles that can extend many meters—in extreme cases far longer.
Where you may see it
Not common in the Mediterranean, but it can drift in and strand on beaches after wind and current shifts.
Sting risk
Very high—its venom can cause severe reactions; contact should be avoided even if it looks “dead” on shore.
5) Fried Egg Jellyfish (Cotylorhiza tuberculata)
Recognizable by a yellowish bell and a central “yolk-like” dome. Often around 30–35 cm across, with short, fine tentacles.
Where you may see it
Very common in the Mediterranean, especially in warm months, often forming groups carried by currents.
Sting risk
Low—usually mild for people; many swimmers see them while snorkeling.
6) Barrel Jellyfish / “Aguamala” (Rhizostoma pulmo)
One of the largest common Mediterranean jellyfish, sometimes reaching up to 90 cm wide. It has a whitish to bluish bell with lobed edges and thick, branched oral arms.
Where you may see it
Mediterranean and also Atlantic waters; may be seen near shore.
Sting risk
Low to moderate—usually not dangerous, but skin reactions can occur, especially in enclosed coastal waters.
7) Mauve Stinger / Bioluminescent Jellyfish (Pelagia noctiluca)
Pink to violet in color, with long stinging tentacles that can reach several meters. The bell is often up to 20 cm. It may glow faintly in the dark.
Where you may see it
Very abundant in the Mediterranean, mainly offshore but often arrives at coasts during blooms.
Sting risk
High—a frequent cause of painful stings and strong skin reactions; can leave open sores in severe cases.
8) By-the-Wind Sailor (Velella velella)
Not a true jellyfish; it is a floating colonial organism. It has an oval blue disk (often a few centimeters long) with a small triangular sail.
Where you may see it
Often appears in large strandings after wind events, washing up in clusters.
Sting risk
Very low—generally harmless to people.
9) Ribbed Jellyfish / Aequorea (Aequorea forskalea)
Transparent bell with visible radial “ribs” that look like pale lines. Up to about 20 cm across, with fine tentacles.
Where you may see it
Open sea and coastal areas; can drift toward shore.
Sting risk
Very low—stings are typically so mild they may not be noticed.
10) Giant Barrel Jellyfish (Rhizostoma luteum)
A large Mediterranean species that can reach around 70 cm in diameter and be quite heavy. The bell is white to yellowish, with thick, branched oral arms that can extend noticeably.
Where you may see it
Rare, but occasionally reported along Spanish Mediterranean coasts.
Sting risk
Low for humans, though it may affect small marine animals.
Other Mediterranean Jellyfish and Look-Alikes
The Mediterranean also hosts many additional species—some native, some occasional visitors, and some expanding their range. Here are more examples you may encounter.
11) Cigar Jellyfish (Olindias muelleri)
A smaller jellyfish sometimes seen in coastal waters; can cause noticeable stings depending on contact.
12) Upside-Down Jellyfish (Cassiopea xamachana)
Often rests on the seafloor with its oral arms facing upward. Contact can irritate skin, especially in shallow lagoons and warm bays.
13) Melon Jellyfish (Cephea cephea)
Round, domed shape that resembles a melon. Usually offshore; sting intensity varies by individual exposure.
14) Orange-Striped Jellyfish (Gonionemus vertens)
A small species that may show stripe-like markings. Contact can be irritating; avoid handling.
15) Blue Button (Porpita porpita)
Not a true jellyfish; a small blue floating hydrozoan. Generally causes minimal irritation for most people.
16) Lobed “Disk Jellyfish” (Lobonema smithii)
A larger disk-shaped jellyfish with lobed structures; encountered occasionally depending on local conditions.
17) Tagus Jellyfish (Catostylus tagi)
A sizable species seen in parts of the Mediterranean and nearby Atlantic influences; typically not among the most dangerous.
18) Mawia benovici
A relatively newly discussed species in Mediterranean reports. Like many jellyfish, it can appear seasonally and in localized areas.
19) Neotima lucullana
A lesser-known jellyfish that may be recorded in Mediterranean biodiversity lists; sightings depend on region and season.
20) Bag Jellyfish (Tripedalia cystophora)
A box-jellyfish relative with distinctive body structure; contact should be avoided as cubozoans can deliver painful stings.
How to Reduce Sting Risk While Swimming
Watch the waterline and floating “spots”
Many stinging species drift near the surface. If you see multiple individuals, it may indicate a larger bloom nearby.
Avoid touching stranded jellyfish
Even on the sand, tentacles can still sting for a while. Use a stick or shovel if one must be moved.
Protect exposed skin
In areas with frequent blooms, a rash guard or thin wetsuit can reduce direct contact.
If stung, act quickly
Rinse gently with seawater (not fresh water) and remove tentacle fragments carefully if visible. If symptoms are severe, widespread, or involve breathing issues, seek medical help promptly.
