They look like something that came from foreign galaxies. Strange looking creatures, shaped like an old-fashioned parachute as they move in jerks through the water. It is a bit spooky to see them move under the surface - sometimes in such large numbers that it seems like the sea water coagulates with another liquid. But the grandiose appearance disappears when we find them washed up on the shore. Then they remind most of all of a lump of jelly.
The ghostly appearance is no less when looking at the evolutionary history of jellyfish. They occur as fossils dating back to the Cambrian era (between 542-488 million years ago), with tentacles and bodies that are practically identical with today's jellyfish.
During his diving expeditions in the waters around the Faroe Islands, the Faroese underwater photographer Ingi Sorensen has taken some fascinating pictures of these living fossils featured now on new Faroese stamps.
Common Jellyfish - Aurelia aurita
Common jellyfish, also called Moon jellyfish or Saucer jelly, is the most common jellyfish in Faroese waters. It belongs to the order Schyhozoa, also referred to as "True jellyfish".
The size of the Common jellyfish is usually about 25 cm in diameter, but can reach 40 cm. It moves mainly by ocean currents and by pulling the saucer together in spurts.
Jellyfish are very primitive animals without most of the organs, which otherwise exist in more evolved animal groups. They don't have brains, lungs, gills or heart. The Common jellyfish absorbs oxygen through a thin membrane, which covers the entire body.
Common jellyfish occurs in the deep of the ocean as well as just below the surface. It absorbs food with the entire body - algae, fish larvae, small crustaceans and amoebas – which are transported to a feeding furrow at the edge of the saucer. If necessary, it may paralyze prey with its burning tentacles, which, however, do not have any notable effect on humans or larger animals.
The most notable about the jellyfish is its reproductive cycle. The four crescent-shaped marks on its saucer are the genitals. There the females carry their eggs, which eventually become small larvae. When the larvae leaves the mother and has lived independent in the sea for some time, it settles on firm ground and develops into a cup-shaped polyp. Eventually constrictions form on the polyp, which then break of and become small jellyfish, the final mature medusa-stage. The larvae and polyp-stage of jellyfish can last for years and in those stages they are asexual, while the final result, the new generation of common jellyfish, are divided into male and female individuals that live for approximately 6 months.
Lion's mane jellyfish - Cyanea capillata
Lion's mane jellyfish is the largest of the true jellyfish. It varies significantly in size, but can become 2.5 m in diameter and have tentacles that are 30 meters long.
Lion's mane jellyfish lives mainly in northern seas and rarely below a depth of 20 meters. It feeds on plankton, small crustaceans and fish, which it stuns with its tentacles. The poison launched from sticky nettles is pretty powerful, and even people can get severe burns on contact with a Lion's mane tentacles. In his final medusa-stage it is assumed that the Lion's mane jellyfish lives approx. one year. But it is possible that the largest specimens, primarily found in arctic regions, are even older.
Reproduction and life cycle of the Lion's mane jellyfish is essentially the same as that of the Common jellyfish.
Mauve stinger - Pelagia noctiluca
The third true jellyfish captured by Ingi Sorensen's lens, is beautiful, but not exactly a welcome guest in Faroese waters. Pelagia noctiluca usually lives in warmer waters like the Mediterranean Sea, the Red Sea and Central Atlantic as well as in the Pacific Ocean. But it has started to occur in more northerly waters, possibly due to climate changes. In 2007, a salmon farm off the coast of Northern Ireland was hit by a 26 square kilometre swarm of young Mauve stingers, and over 100,000 salmon were killed.
Pelagia noctiluca has an almost bell-shaped saucer, usually about 10 cm in diameter, but can become up to 30 cm. From the saucer hang 8 tentacles with a quite potent toxin, which can cause searing burns on humans and trigger allergic reactions. From the combined mouth and anus organ in the center of the saucer, hang four tentacles which are used for holding prey and carry it to the mouth. They reproduce sexually, but the offspring do not have the same polyp stage as Common jellyfish. Instead they develop from larvae to medusa while still swimming in the sea. Pelagia noctiluca means something like "sea - night light" and the name refers to the fact, that the jellyfish produces a fluorescent light when disturbed, for example by ships or waves.
Melon jellyfish - Beroe cucumis
Melon jellyfish belong to the order comb jellies (Ctenophora), which are more evolved than true jellyfish. They can be recognized by their eight ribs or combs, running from the front to the rear. The comb jellies' ribs can glow in the dark, but the function of the light is unknown. Most ctenophores are hermaphrodites and can fertilize themselves and others. Some species can even multiply already in the larval stage, and these characteristics can, under the right conditions, cause an explosive increase in numbers.
Unlike the true jellyfish, the larvae of the comb jelly do not have a polyp stage – instead they slowly develop into adulthood.
The Melon jellyfish is shaped like a bag and becomes 10-15 cm long. It has neither tentacles, like other ctenophores, or poisonous nettles like true jellyfish. It swims using cilia on the ribs and has quite good control over its movements, which makes it a phenomenal hunter. It hunts and eats mainly other comb jellies, which are swallowed whole through the mouth at the top of the head.