The EcoJel Project - Understanding Jellyfish In The Irish Sea The EcoJel Project - Understanding Jellyfish In The Irish Sea
The Big JellyFish Hunt - Ecojel

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Irish Sea Jellyfish

The Common Jellyfish

Aurelia aurita - the most familiar jellyfish
Key features: Four purplish/pink gonad rings. The rest of the jellyfish is transparent and has numerous short tentacles around the margin of the bell (difficult to see when out of water).
Size: Up to 40 cm in diameter, normally smaller.
Distribution: Present in all coastal waters and throughout the Irish Sea. It can form very dense aggregations. Present from April to September.
Sting: Only a mild sting.

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The Barrel Jellyfish

Rhizostoma octopus - a conspicuous jellyfish
Key features: Surprisingly solid large jellyfish. The bell is shaped like a dome and has a ghost white colour with purple/blue lobes around the margin. Eight solid oral-arms that resemble a cauliflower. No tentacles.
Size: Up to 1m in diameter. We have measured a barrel jellyfish of 80 cm in diameter and weighing 35 kg!
Distribution: Forms dense aggregations in coastal areas (Rosslare, Tremadoc and Carmarthen Bays) during summer months. Some individuals sighted or caught in the Irish Sea and off the South coast of Ireland during the winter.
Sting: No tentacles but can cause irritation.

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The Compass Jellyfish

Chrysaora hysoscella - most striking jellyfish
Key features: Reddish brown “V” shaped markings on the bell. Four frilly long trailing oral arms. 24 tentacles dangling from the margin of the bell.
Size: Up to 50 cm in diameter.
Distribution: Found mainly off the West and South coast of Ireland and the South coast of Wales, but occur also in the Irish Sea. Is more abundant during July to September.
Sting: Painful sting sometimes compared to a nettle sting.

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The Blue Jellyfish

Cyanea lamarckii - The Blue Jellyfish
Key features: Blue body. However, individuals can be completely translucent or present a yellowish colour. The bell has 8 lobes. Masses of tentacles on the margin.
Size: Up to 30 cm in diameter.
Distribution: Can be found throughout the Irish Sea. Occurs from April to July.
Sting: Painful sting.

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The Lion’s Mane

Cyanea capillata - most venemous jellyfish
Key features: Large flat bell, red or dark brown in colour. Small individuals can have a yellowish colour. Masses of many long tentacles. 
Size: Up to > 1m in diameter, but usually much smaller.
Distribution: Mostly in the northern half of the Irish Sea. Particularly present in Dublin Bay. Occurs from May/June to September.
Sting: WARNING! Severe sting! 

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The Mauve Stinger

Pelagia noctiluca - The Mauve Stinger
Key features: Translucent bell with sometimes warts or bumps on top. Eight shoe-lace-like tentacles. Colour can be quite variable. Smaller individuals (euro coin size) are often golden brown in colour with some ‘compass jellyfish’ like ‘v’ shape markings. Larger individuals are more transparent with pink/mauve colour. May look like the moon jellyfish.
Size: Very small, up to the size of a closed fist.
Distribution: Mostly on the Atlantic coast (North, West and South of Ireland), in autumn.
Sting: Painful sting.

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Other Gelatinous Organisms That You May Observe:

Portuguese Man-O-War

Physalia physalis - an unusual siphonophore
Key features: Large and conspicuous silver-blue float with red/pink tinging. Looks like a Cornish pastie shaped balloon! This jellyfish is a colony of medusae and polyp like individuals. Tentacles may be several meters long. Floats on the sea surface.
Size: Float up to 30 cm long and 100 mm wide.
Distribution: Normally an oceanic species, but can occur in Irish waters after persistent south westerlies.
Sting: WARNING! Severe stings! Has caused 3 fatalities in America.

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Other Siphonophores

Siphonophores
Key features: Long and thin lengths of clear jelly (several cm to m long). Extremely fragile. These are colonial animals. Most visible species in Irish and UK waters is Apolemia uvaria which looks like a frayed piece of rope. Do not float on the surface.
Size: Several centimetres to several meters long.
Distribution: More frequent in oceanic waters, so off south and south west coasts of Ireland and UK.
Sting: Some have a very strong sting!

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Crystal Jellyfish

Aequorea sp - Crystal jellyfish
Key features: Almost completely transparent. Bell is quite solid, thickest in centre, with 60-80 lines radiating from a central ring. Similar number of fine tentacles.
Size: Up to 40cm in diameter. 
Distribution: In all Irish & UK waters.
Sting: Unknown.

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Little Jellyfish

The hydromedusae - Little jellyfish
Key features: There are approximately 30 species of little jellyfish in Irish and UK waters. Most of these are very small and will not be observed without the aid of a stereoscope. However, some such as Leuckartiara or Aglantha can be 10-20 mm long and have some colour.
Size: Very small. Most <20 mm.
Distribution: Everywhere
Sting: Mild to moderate.

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Sea Gooseberry

Pleurobrachia pileus - Sea gooseberry
Key features: Shaped like a gooseberry and is transparent. 8 ciliary plates or comb rows. In water can see two long trailing filaments/tentacles (note tentacles are sticky and don’t sting).
Size: Up to 2 cm long
Distribution: Everywhere
Sting: No sting

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Comb Jellyfish

Beroe sp. - Comb jellyfish
Key features: This comb jelly is shaped like a plum tomato (so oval in shape). It is much larger than the sea gooseberry on which it feeds. It has a lavender colour and eight rows of beating ‘combs (cilia)’ that send iridescent colours along the edges. They have no tentacles.
Size: Up to 15 cm long.
Distribution: All Irish and UK waters.
Sting: No sting.

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Salps

Salps
Key features: Barrel shaped animals, mostly transparent with visible muscle bands almost forming continuous hoops around the ‘barrel’.
Size: Up to 15-20 cm long but also forms chains of individuals.
Distribution: Oceanic waters mostly.
Sting: No sting.

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Types

» Common
» Barrel
» Compass
» Blue
» Lion's Mane
» Mauve Stinger
» Man-O-War
» Siphonophores
» Crystal Jellyfish
» Little Jellyfish
» Sea Gooseberry
» Comb Jellyfish
» Salps

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