There are 302 species of cnidarians (phylum Cnidaria) recorded in Ireland.^[1]

The cnidarians' distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. They have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both (hence they are trimorphic).^[2][3][4]

Cnidarians found in Ireland and Irish waters include sea pens, sea anemones, hydroids, sea jellies ("jellyfish") and corals.

Class Anthozoa

Order Actiniaria (sea anemones)

Family Actiniidae

Actinia fragacea (strawberry anemone)

• Actinia equina (beadlet anemone)
• Actinia fragacea (strawberry anemone)
• Anemonia viridis (snakelocks anemone)
• Anthopleura ballii (red speckled anemone)
• Aulactinia verrucosa (gem anemone)
• Urticina eques
• Urticina felina (northern red anemones, dahlia anemone)

Family Actinostolidae

Stomphia coccinea

• Stomphia coccinea

Family Aiptasiidae

• Aiptasia mutabilis

Family Capneidae

• Capnea sanguinea

Family Edwardsiidae

• Edwardsia claparedii
• Edwardsia delapiae
• Edwardsia timida (timid burrowing anemone)
• Edwardsiella carnea
• Scolanthus callimorphus

Family Gonactiniidae

• Gonactinia prolifera

Family Halcampidae

• Halcampa chrysanthellum

Family Halcampoididae

• Halcampoides elongatus

Family Haloclavidae

• Mesacmaea mitchellii
• Peachia cylindrica

Family Hormathiidae

Calliactis parasitica living on the shell of a common whelk, occupied by soldier crab.

• Adamsia carciniopados
• Adamsia palliata (cloak anemone)
• Calliactis parasitica
• Cataphellia brodricii
• Hormathia coronata

Family Metridiidae

• Metridium senile (plumose anemone, frilled anemone)

Family Sagartiidae

• Actinothoe sphyrodeta
• Cereus pedunculatus (daisy anemone)
• Phellia gausapata
• Sagartia elegans
• Sagartia ornata
• Sagartia troglodytes (mud sagartia, cave-dwelling anemone)
• Sagartiogeton laceratus
• Sagartiogeton undatus

Order Alcyonacea (soft corals)

Family Alcyoniidae

Alcyonium digitatum (dead man's fingers)

• Alcyonium digitatum (dead man's fingers)
• Alcyonium glomeratum (red sea fingers)
• Alcyonium hibernicum (pink sea fingers)
• Parerythropodium coralloides

Family Gorgoniidae

Eunicella verrucosa

• Eunicella verrucosa (broad sea fan, pink sea fan, warty gorgonian)

Family Plexauridae

• Swiftia pallida (northern sea fan)

Order Ceriantharia (tube-dwelling anemone)

Family Arachnactidae

Arachnanthus sarsi, photographed off Rathlin Island

• Arachnanthus sarsi

Family Cerianthidae

Pachycerianthus multiplicatus (firework anemone)

• Cerianthus lloydii (lesser cylinder anemone)
• Pachycerianthus multiplicatus (firework anemone)

Order Zoantharia

Family Epizoanthidae

• Epizoanthus couchii

Family Parazoanthidae

Isozoanthus sulcatus in Lough Hyne

• Isozoanthus sulcatus
• Parazoanthus anguicomus
• Parazoanthus axinellae (yellow cluster anemone)

Class Hydrozoa

Order Anthoathecata (athecate hydroids)

Family Bougainvilliidae

Bougainvillia muscus

• Bougainvillia muscus
• Garveia nutans

Family Candelabridae

• Candelabrum phrygium

Family Corymorphidae

• Corymorpha nutans

Family Corynidae

• Coryne eximia
• Coryne muscoides
• Sarsia densa

Family Eudendriidae

Spanish shawl feeding on Eudendrium ramosum

• Eudendrium annulatum
• Eudendrium arbuscula
• Eudendrium ramosum

Family Hydractiniidae

Clava multicornis

• Clava multicornis
• Hydractinia echinata (snail fur)

Family Hydridae (hydras)

• Hydra viridissima (green hydra)^[5]
• Hydra vulgaris (common hydra)^[5]

Family Pandeiidae

• Leuckartiara octona
• Neoturris pileata

Family Porpitidae (chondrophores)

Velella velella colony

• Velella velella (sea raft, by-the-wind sailor, purple sail, little sail)

Family Tubulariidae

Tubularia indivisa (oaten pipes hydroid)

• Ectopleura larynx
• Tubularia indivisa (oaten pipes hydroid)

Order Limnomedusae

Family Olindiidae

Craspedacusta sowerbii

• Craspedacusta sowerbii^[6]

Order Siphonophorae (siphonophores)

Family Apolemiidae

Apolemia uvaria (string jellyfish)

• Apolemia uvaria (string jellyfish, barbed wire jellyfish, long stringy stingy thingy)

Family Physaliidae

Portuguese man-o'-war

• Physalia physalis (Portuguese man-o'-war, blue bottle, floating terror)

Class Scyphozoa (true sea jellies)

Order Rhizostomeae

Family Rhizostomatidae

Rhizostoma pulmo

• Rhizostoma pulmo (barrel jelly, dustbin-lid jelly, frilly-mouthed jelly)

Order Semaeostomeae (flag-mouth sea jellies)

Family Cyaneidae

Cyanea capillata (lion's mane jelly)

• Cyanea capillata (lion's mane jelly)
• Cyanea lamarckii (blue jelly, bluefire)

Family Pelagiidae

• Chrysaora hysoscella (compass jelly)
• Pelagia noctiluca (mauve stinger)

Family Ulmaridae

• Aurelia aurita (moon jelly, common jelly, saucer jelly)

Order Scleractinia (stony corals, hard corals)

Family Caryophylliidae

Caryophyllia smithii

• Caryophyllia inornata
• Caryophyllia smithii (Devonshire cup coral)
• Lophelia pertusa^[7]

Family Oculinidae

Zigzag coral

• Madrepora oculata (zigzag coral)^[7]

Class Staurozoa

References

• World Register of Marine Species

External links

• Marine species identification portal