Jellyfish

Jellyfish is a life stage of cnidarians (Cnidaria). Jellyfish themselves are not a systematic taxonomic group. They belong to the oldest animals in the history of the earth. More than 2,600 species are known.

Typical for many jellyfish is a generational change, in which a fixed stage (polyp) and a medusa or jellyfish stage moving freely in the water alternate regularly. The polyp produces asexually, e.g. by sprouting, free swimming medusas, which form a larva by sexual reproduction (via germ cells), which settles and differentiates again to the polyp. The free-swimming development stage, the actual jellyfish, is therefore only a part of the life cycle of a species.

This life cycle is typical for cnidarians of the classes scyphozoans (umbrella jellyfish), cubozoans (cube jellyfish) and hydrozoans.

Most jellyfish have long tentacles equipped with cnidoblasts. They use them for catching prey and for defense. The stinging cells (nematocytes) are scattered over the tentacles and contain a highly effective toxin. On their surface they carry a sensory hair which is in direct contact with the toxin-containing nettle capsule. If touched, the nettle capsule explodes. An internal stiletto-shaped device is shot out with a pressure of 150 bar and anchors itself in the tissue of the prey. Within a few nanoseconds, the toxin contained in the nettle capsule is injected. In addition, the nettle thread is usually covered with drill spikes. After use, the nettle capsules are rejected and re-formed.

The nettle toxins are proteins (cytolysins, neurotaxins) which have a cell- or nerve-damaging effect. The clinical picture of urticaria (see below: Dermatitis medusica) depends on the duration, extent (surface infestation) and intensity of contact with the urticaria organs as well as on the physical constitution of the person affected (age, weight, state of health).

Accidents with jellyfish are usually treated on the spot. In medical facilities, patients with nettings from holiday countries are seen, which are usually some time ago.

Flower animals (anthozoans)

With over 7000 species, this is the largest class within the cnidarians. The best known representative is the sea anemone, which grows as "flower-like" polyps on solid ground. They can be found in all seas from shallow water to 10,000 m depth. The neurotoxins of this jellyfish species are harmless to humans.

Screen jellyfish (Scyphozen)

Umbrella jellyfish are also found in large quantities in the North Sea and Baltic Sea worldwide. Here the most common representatives are ear and fire jellyfish.

Jellyfish

Visitors to the North Sea and Baltic Sea often get to see these harmless jellyfish with their large umbrella. The poison of the ear jellyfish does not cause a noticeable skin reaction in humans.

Yellow hair jellyfish (fire jellyfish)

This jellyfish species occurs in the North Atlantic as well as in the North Sea and the western Baltic Sea. It is characterized by its yellow-orange screen and long tentacles. The netting leads to painful redness and itching; blistery reactions or cardiovascular problems are less frequent.

Cube Jellyfish(Cubozoen)

Its name is derived from its cuboid or cubic shape. Their tentacles can be up to 3 m long. They populate all tropical and subtropical seas worldwide and are fast swimmers. Occasionally they were also found off the Portuguese coast as well as in the Mediterranean.

Carukia barnesi

Carukia barnesi, a very small cube jellyfish, whose screen is hardly more than 1.0 cm in size, triggers Irukandji syndrome on contact with the skin, with severe abdominal radiating back pain lasting days to weeks. Deaths are not known

Sea wasps (Chironex fleckeri)

The best known representative of the cube jellyfish is the sea wasp , which is found in large numbers on the north and east coast of Australia. The sea wasp is considered to be the most poisonous sea animal of all. Every year more people die from the consequences of a sea wasp netting than from shark attacks! The neurotoxic poison leads to paralysis of the skeletal and heart muscles and, depending on the extent of the poisoning, to cardiac arrest.

The sea wasp season lasts from November to May. During this time, bathing in seas rich in sea wasps should be avoided. Sea wasps washed up on the beach should not be touched. The nettle cells remain intact for weeks, even when the jellyfish are dried-out.

Hydrates (Hydrozoans)

The most important representative is the Portuguese galley (Physalia physalis), which lives off Australia and on the coasts of the Pacific and Atlantic. Its hives poison can be fatal in weakened persons or children in extreme cases. Although the shape of this jellyfish species is reminiscent of a classic jellyfish, it consists of a whole colony of different polyp colonies. Physalia physalis occurs mainly in tropical and subtropical regions (also off the coasts of the Canary Islands, Portugal, northern Spain and in the Mediterranean Sea off Mallorca and Ibiza). Its tentacles are up to 30 m long.

Contact with sources can lead to entanglement of different types and strengths; see below Dermatitis medusica (Jellyfish dermatitis).

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