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Poisonous animals
Cnidarians (Jellyfish, Corals and Anemones)
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Various anthozoans and other hydrozoans that can cause envenoming in humans

Clinical entries

For clinical data see section “Risk” below


(See also above: "General information on cnidarians")


Coelenterata; Cnidaria

Common names


In the following summary, coelenterates whose stings generally only cause local effects are discussed. Nonetheless, they can also cause secondary infections with a lengthy healing process, as well as allergic and even anaphylactic reactions. Severe stings have been observed after contact with the Limnomedusae listed below.



Milleporidae: Millepora sp. (Fire corals, False corals, Stinging corals, Feuerkorallen). Found in reef areas of tropical seas, in shallow water and up to depths of 30 m. They do not belong to the true corals, but like them do form sessile polyp colonies with a highly branched, sharp-edged calcium carbonate skeleton (Fig. 4.16). They range in diameter from a few centimetres to 2 m. Touching or grazing against them causes immediate burning pain and pruritus. Urticarial symptoms follow. The pain usually disappears after 30–90 min, and the skin symptoms after 3–7 days. M. alcicornis is probably responsible for more accidents than any other species of coelenterate (Jones 1909).


Treatment: symptomatic.

Fig. 4.16 Millepora sp.

Plumulariidae (Feather hydroids, Federpolypen): coastal regions of tropical to cool seas and oceans. Several species of the genera Aglaophenia and Lytocarpus have been associated with itching and burning skin irritations. These are polyp colonies of a few centimetres to 1 m in size. They have many feather-like branches and have an elastic consistency (Fig. 4.17).


First aid: wash off undischarged nematocysts remaining on the skin with water. Cold packs to treat pain (Rifkin et al. 1993).


Treatment: symptomatic.

Fig. 4.17 Lytocarpus sp.


Limnomedusae (Trachymedusae): there is no polyp stage in this group of hydrozoans. The free-swimming, smaller medusae generally have tentacles on the edge of their bell. Gonionemus sp. and Olindioides sp. have been reported to cause stings in humans. Whereas the Pacific Northwest Gonionemus vertens (bell diameter 1.5–2.5 cm) lacks a sting that is felt by people, the same species in the Russian Far East is reported to cause systemic effects. Another species causing systemic effects is the Japanese Gonionemus oshoro. Gonionemus sp. have also been associated with the "Irukandji syndrome" (Warrell and Fenner 1993).

Olindioides formosa is a nearshore limnomedusa that inhabits quiet waters of northern Japan and Kamchatka (Russia) and the region from Alaska's Aleutian Islands to northern California. Olindioides formosa has been known to cause severe envenoming in Japan, as well as Olindias sambaquiensis in the southwestern Atlantic ocean, along the coasts of Brazil, Uruguay and Argentina.


Treatment: symptomatic.



Actinaria (Anemones, Seeanemonen, Aktinien, Blumentiere). Found throughout the world in tropical to cold seas. Sessile, flower-like coelenterates, often brightly coloured. They do not have a calcium carbonate skeleton. The largest representatives reach a diameter of 0.5 m. In contrast to many colony-forming coelenterates, sea anemones represent a single individual.

Many species cause stings, but they are generally not serious. For example, contact with Anemonia sulcata (snakelocks anemone, Fig. 4.18), common in the northeastern Atlantic, barely causes noticeable effects. Nonetheless, contact with mucous membranes of more sensitive skin areas (face, genital region) can cause local paraesthesias, oedema and erythema. In more severe cases ulceration can occur. Similar local effects are caused by stings from Phyllodiscus semoni from Okinawa, Japan, or by Actinodendron plumosum in the Indo-Pacific region. The latter can also cause generalised effects such as fever, chills, abdominal pain, nausea, vomiting and headache (Hansen and Halstead 1971, Maretic and Russell 1983).


Fig. 4.18 Anemonia sulcata


"Sponge fisherman's disease" is caused by sea anemones (Sagartia sp. or Actinia sp.) that live on the bottom of sponges. These are said to cause not only local effects but also sometimes systemic effects such as headache, nausea, vomiting, fever, chills and muscle spasms.

Treatment: symptomatic.


Madreporaria (Steinkorallen, Stony corals): typical reef corals in tropical and subtropical coastal regions. Injuries caused by stony corals are mostly external in nature. Minor cuts and grazes are easily caused by the sharp-edged calcium carbonate skeleton. Such injuries can be very painful, as toxic secretions from nematocysts enter the wound when the injury occurs. Several species of the genera Acropora, Astreopora, Goniopora and Fungia can lead to stings with local effects simply through contact.

Treatment: symptomatic.


Zoantharia (also known as Zoanthidae, zoanthids, Krustenanemonen)

Zoanthids are colonial anemones mainly growing in coral reefs but also in other marine environments around the world. Their taxonomy poses some problems and awaits reconsidering. Zoanthids are quite popular among marine aquarium enthusiasts, sometimes also kept unintendedly. Some species are toxic, containing palytoxin. Palytoxin (PTX or PLTX), first described from Palythoa toxica from Hawai, is one of the most potent natural toxins discovered ever: 1 g is enough to kill 150'000 mice.

PTX was detected also in the Japanese Palythoa magaritae and in the sea anemone Radianthus macrodactylus from the Seychelle Islands. Analgoges of PTX were also described from the red alga Chondria armata and the dinoflagellates Ostreopsis siamensis, O. mascarenensis from the Indian Ocean, as well as from Mediterranean Ostreopsis ovata. Meanwhile it has been shown that PTX is extensively distributed in the food chain of reef communitees of the Carribbean and the Pacific ocean, where it can cause severe poisonings when eaten by human beeings (see "Palytoxin poisoning" in the group of poisonous animals).


Various species in the zoanthid genera Palythoa, Protopalythoa, Zoanthus, Parazoanthus have been claimed to contain palytoxin. However a recent investigation on the content of PTX in zoanthids showed that some of the species commonly sold in the home aquarium trade are non-toxic or only weakly toxic (Palythoa mutuki, Zoanthus sansibaricus, Zoanthus kuroshio), in contrast to a highly toxic variety of Palythoa sp. (possibly P. heliodiscus or P. toxica) which is also available (Deeds et al. 2011).


Zoanthids are quite easily imported as "bycatch" or "hitchhikers" on living stones by private aquarists and even professional keepers in zoos or aquarium shows. Usually these are overgrown, fragmented limestones from the wild or other aquarias.

PTX in some zoanthids may pose a risk to the owners when they inhale aerosols while removing them from the aquarium or after dermal exposures. Two keepers from the Basel Zoo showed marked symptoms similar to those described below after brushing lime stones. The stones were lying in a dry place for months or even years; they have been in an aquarium once where they were overgrown by Palythoa sp..


During summer 2005 around 200 people showed symptoms of rhinorrhea, cough, fever, bronchoconstriction with mild dyspnea and wheezes while working or recreating at the beach of Genova, Italy. Conjunctivitis was also observed in some cases, and 20 people required extended hospitalization. It seems that the patients inhaled aerosols deriving from the dinoflagellate Ostreopsis ovata wich proliferated enormously in that same time and area; molluscs, echinoderms, crustaceans and small fish were suffering also. Mass spectrometry reveald that these planctonic organisms contained PTX (Ciminello et al. 2006).



Hoffmann et al (2008): 1 case of palytoxin poisoning due to cuts with Parazoanthus sp. inflicetd during cleaning of sea water aquarium with zoanthid colonies. Identification: specimen available for identification, sample contained high concentration of PTX.

Symptoms and signs: Shivering, myalgia, general weakness starting 2 hours after the injury with increasing intensity. Collapse and speech disturbances 16 hours after the injury. Erythema and swelling of the fingers where the cuts were inflicted with paraesthesia and numbness spreading across the entire arm within 20 hours. Incomplete right bundle branch block. Elevated creatine kinase and lactate dehydrogenase. All signs and symptoms cleared within days.


Treatment: symptomatic



Literature: Cleland and Southcott 1965, Deeds and Schwartz 2010, Deeds et al. 2011, Halstead 1988, Heeger 1998, Auerbach and Halstead  1989, Southcott 1987a,b, Storch and Welsch 1997, Williamson et al. 1996