Especially in the spring and summer you can encounter thousands of jellyfish on the beach. The skeletal animals consist of more than 95 percent water and have characteristic fringe-like mouth arms. Not only their appearance, but also their life course is very unique in the animal kingdom. Jellyfish start life as an egg, grow from a polyp and then live as an adult jellyfish. Research shows that they evolve back to their young stage. Are these animals immortal?
300 million year old fossil / Source: James St. John, Wikimedia Commons (CC BY-2.0)
The origin of jellyfish
Jellyfish originated 500 million years ago in the Cambrian geological period (488 – 542 million years ago). During the Cambrian, the temperature on Earth was high and violent volcanic eruptions characterized our planet. The volcanic eruptions spewed out substances such as methane and carbon monoxide that were ideal for the further development of amino acids. Amino acids are acids that are the building blocks for proteins in body cells. Proteins are indispensable for organisms (including humans) as they, among other things, ensure the communication between cells and regulate metabolic processes. The proteins produced single-celled organisms (bacteria) living in the sea. These continued to multiply and take the form of jellyfish – the first marine animals on Earth.
Despite the various mass extinctions that have taken place over millions of years, jellyfish have survived every time. Since the Cambrian, the appearance of jellyfish has hardly changed and four thousand species have emerged.
The anatomy of jellyfish
Reproduction and life cycle
Many jellyfish are hermaphrodites and thus have both the male and female sex organs. The unisexual male jellyfish discharge their sperm into the sea and thus reach the females. Planulas (jellyfish larvae) emerge from the fertilized eggs and swim around freely, looking for substrate (a stable surface) to attach themselves to. The planulas grow into a gelatinous polyp that is very similar to a plant. The polyp always makes a saucer-shaped cord on the top, so that several saucers are stacked on top of each other. Then the saucers separate from the polyp one by one. As soon as the saucer-shaped animals turn around, the bells (inverted saucers) become clearly visible.
No skeleton and a lot of water
Jellyfish consist of 95% to 99% water. They do not have a skeleton and cannot hear or see. Most jellyfish (disc jellyfish) are made up of a bell that consists of two skin layers of cell membrane (a mixture of mainly protein and fat). There is a jelly layer between the outer and inner skin layers. Around the clock are nerve cells, with which the animals can receive light and taste it. Since jellyfish do not have a brain, they cannot register pain, but because they do have nerve cells, they can feel changes in their environment. In addition, there are cilia around the clock that transfer the oxygen in the water to the jellyfish and ensure that the animals can move about.
Tentacles and nettle cells
Inside the clock is a body opening, a stomach and several sex organs. Food is consumed and excreted through the body opening that connects the jellyfish to the open sea. A number of fringe-like wisps, the so-called mouth arms, emerge from the body opening with which food is brought to the opening. At the edge of the body opening are tentacles with nettle cells that contain small poisonous harpoons. With the poison, the jellyfish paralyzes or kills its enemy.
The diet consists mainly of plankton, but also larvae of crabs and lobsters, arrowworms, copepods, young herring and small jellyfish species are also eaten. Animals that in turn eat jellyfish are sea turtles, sea anemones and sea snails. Jellyfish are also on the menu in China, Japan and Iceland. A jellyfish sandwich is not exceptional there.
Are jellyfish immortal?
Old jellyfish become young again
Jellyfish that live in captivity generally have a shorter life span than wild jellyfish. Until 2011, scientists were less concerned with the ages of the wide variety of jellyfish species. At the end of 2011, Chinese biology student Junru He collected two polyps from ear jellyfish from Xiamen Bay, China. The ear jellyfish is one of the most common jellyfish species in the world and lives in almost all oceans. Junru He raised the polyps in an aquarium with seawater from the bay. At the end of 2015 he presented his remarkable results. When the jellyfish had grown into an adult jellyfish, they transformed back to the polyp stage and then back to an adult stage. This particular phenomenon continued to occur continuously.
The ability to regenerate
As the jellyfish multiplied, the aquarium quickly became overcrowded. Because of this, they attacked each other in the battle for food. The jellyfish that lost a mouth or suffered damage regenerated themselves. She made new body parts from cells and completely repaired their damage. Since the presentation of the analysis results, many scientists have been studying the special ear jellyfish that appears to be unable to die of old age.
Which jellyfish live in the North Sea and which sting?
Stinging jellyfish
Of the many jellyfish species that exist, some temporarily visit our shoreline to forage. Then, around winter, they swim to warmer water or seek out the depths (up to 1000 meters) of the ocean. All jellyfish sting, including those that live in the North Sea, but we don’t always feel it. The nettle cells in the tentacles of some jellyfish cannot penetrate our overly thick skin. There are only three types that can penetrate our skin: the blue hair jellyfish, yellow hair jellyfish and compass jellyfish.
The ear jellyfish
The ear jellyfish (Aurelia aurita) is one of the most common jellyfish species in the North Sea. This colorless jellyfish can grow ten to forty centimeters wide and gets its name from its genitals. These organs resemble four (in exceptional cases more) ears and can be white (male) or pink (female). The nettle cells are filled with poison, but can only be felt by other animals. It can be found on the Dutch coast from April to September.
The soap mushroom
The soap mushroom, also called cauliflower jellyfish (Rhizostoma pulmo) with its ninety centimeters in diameter, it is the largest jellyfish in the Netherlands. The jellyfish has a light blue bell with a dark blue border (male) or a light brown bell with a dark brown border (female) and eight white mouth arms. The soap mushroom sting is so weak that people don’t feel it. The jellyfish is found in the North Sea from August to November.
The blue and yellow hair jellyfish
The blue hair jellyfish (Cyanea lamarckii) has a thirty centimeter bell and up to sixty-five tentacles. It can be found in the North Sea from March to August. In contrast to the very common blue hair jellyfish is the yellow hair jellyfish (Cyanea capillata) fairly rare in our coastal waters. If we find the yellow hair jellyfish on our beaches, it will be in the fall and it will not be larger than fifty centimeters. The yellow and sometimes red colored jellyfish has no less than one hundred and fifty tentacles. The bell can reach over two meters in diameter and the tentacles can reach a length of thirty-seven meters. The yellow hair jellyfish is therefore the largest jellyfish in the world. Contact with the tentacles of both species produces a sensation similar to that of nettles.
Ear jellyfish with six ears / Source: Saivo
Soap mushroom / Source: KosovareK, Wikimedia Commons (CC BY-SA-3.0)
Blue hair jellyfish / Source: Saivo
The compass jellyfish
The compass jellyfish (Chrysaora hysoscella) as the name suggests has a pattern resembling a compass rose. The colorless clock shows sixteen red-brown V-shapes. The bell has a diameter of ten to thirty centimeters and from the bell hang twenty-four tentacles that can reach a length of two meters. Like the blue and yellow hair jellyfish, the stings of the compass jellyfish give a burning sensation. The jellyfish lives in our coastal waters six months a year (May to August).
The sea grape
The sea grape (Pleurobrachia pileus) is a different jellyfish species than the above slide jellyfish, because it has no bell. With its spherical body over which vertical ribs run, the jellyfish belongs to the comb jellyfish. The transparent sea grape, unlike some other comb jellyfish, has tentacles. The tentacles (only two pieces) do not contain any stinging cells and therefore cannot release poison. The jellyfish moves through cilia on the ribs and thus also waves water (with oxygen and food) towards it. The jellyfish, up to three centimeters in size, wash up on Dutch beaches, especially in spring. As soon as they wash up they retract their tentacles so that you only see a grape-shaped animal.
Yellow hair jellyfish / Source: Saivo
Compass jellyfish / Source: Saivo
Sea grape / Source: Zeisterre, Wikimedia Commons (CC BY-SA-3.0)
Jellyfish bites
Risks of jellyfish bites
Once the red flag is raised, it is too dangerous to swim in the sea. One reason can be a large amount of jellyfish. If you get out of the water too late, you run the risk of being stung. Jellyfish lying on the stand can also sting. A jellyfish that washes ashore and is not taken back by the sea will live for several hours before it dies. During those hours the stinging cells are still active.
Symptoms and Treatment
Common symptoms of a jellyfish bite are itching and redness around the injured area and dizziness. It is recommended to go directly to the lifeguard. They will apply a special ointment to the wound that will allow the poison to be removed from the body in about ten minutes. If there is no lifeguard in the area, rinse the skin with hot water to make the poison harmless. Another option is to rinse the skin with sea water. Then remove the possible remains of the tentacles from the skin with tweezers or a card (such as a debit card). An aspirin may be taken to reduce pain.
When do you call the emergency service?
If the complaints are more serious than itching and dizziness (such as vomiting, palpitations, breathing problems or headache) then this is an allergic reaction. If you recognize the symptoms, call emergency services. The emergency service must also be called in if you have been stung in several places, on and around the eyes or genitals, or if the standard complaints have not disappeared after twenty-four hours.
The most poisonous jellyfish in the world: the Australian sea wasp
Bites from the Australian sea wasp (Chironex fleckeri) are a completely different story. The animal that lives in the waters of Northeast Australia, New Guinea, Indonesia, the Philippines and Vietnam is among the most poisonous in the world and is the most poisonous of all jellyfish. This square jellyfish grows to a maximum size of 12 inches and has 15 tentacles at each corner that can be three meters long. The poison in the tentacles’ nettle cells is so toxic that people who are stung lose consciousness and die within minutes. The danger with the cube jellyfish is that it is only visible at a distance of ten centimeters and people are often stung before that, which feels like hundreds of needles in the skin.
