Jellyfish are anatomically relatively simple animals; they lack not just brains, but also blood and bones, and possess only rudimentary sense organs. Despite their name, jellyfish aren’t, of course, fish. In fact jellyfish species aren’t any one thing.
Many of the creatures lumped together as jellyfish are no more closely related than, say, horseflies are to horses. Not only do they occupy disparate branches of the animal family tree, but they also live in different habitats; some like the ocean surface, others the depths, and a few prefer freshwater. What unites them is that they’ve converged on a similarly successful strategy for floating through life: Their bodies are gelatinous.
Though more than 2,000 jellyfish species that have already been discovered, that’s thought to be only a small fraction of what actually exists. Free-swimming scyphozoan jellyfish occur in all oceans and include the familiar disk-shaped animals that are often found drifting along the shoreline. Most live for only a few weeks, but some are known to survive a year or longer. The bodies of most range in size from about 2 to 40 cm (1 to 16 inches) in diameter; some species are considerably larger, however, with diameters of up to 2 metres (6.6 feet). Scyphozoan medusae consist of almost 99 percent water as a result of the composition of the jelly that forms the bulk in nearly all species. Most feed on copepods, fish larvae, and other small animals that they catch in their tentacles, which have stinging cells (nematocysts). Some, however, simply suspend feed, extracting minute animals and algae (phytoplankton) from the water. Like all cnidarians, their bodies are made up of two cellular layers, the ectoderm and the endoderm, between which lies the gelatinous mesoglea. In jellyfish the transparent mesoglea layer is quite thick.
The life cycle of free-swimming scyphozoan jellyfish typically consists of three stages. A sessile polyp (scyphistoma) stage asexually buds off young medusae from its upper end, with each such ephyra growing into an adult. The adults are either male or female, but in some species they change their sex as they age. In many species, normal fusion of egg and sperm results in an embryo that is brooded in the gut of the adult until it becomes a ciliated planula larva, but in some this development takes place in the sea. After the planula larva leaves its parent, it lives for a time in the plankton and eventually attaches to a rock or other solid surface, where it grows into a new scyphistoma. Such a life cycle characterizes the order Semaeostomeae, which contains some 50 species of mainly coastal-water jellyfish, several of which have very wide geographic ranges. Included among these are members of the genera Aurelia and Chrysaora and the big red jellyfish, Tiburonia granrojo (subfamily Tiburoniinae), one of only three species of jellyfish that lack tentacles.
Jellyfish species transition between two different body forms throughout their lives. The familiar body plan that looks like an upside down bell with tentacles hanging down from the inside is called the medusa. The polyp, the other cnidarian body plan, is the opposite, with the mouth and tentacles above, like a sea anemone.
Jellyfish also have a stinging adaptation that is unique to them and their close relatives (including sea anemones and hydras): nematocysts, or stinging cells.
Brains of Jelly?
Jellies don’t have brains as we typically think of them: rather, they have a network of neurons (“nerve net”) that allows jellies to sense their environments, such as changes in water chemistry indicating food or the touch of another animal. The nerve net has some specialized structures such as statocysts, which are balance sensors that help jellies know whether they are facing up or down, and light-sensing organs called ocelli, which can sense the presence and absence of light.
Additionally, some jellyfish have sensory structures called rhopalia, which contain receptors to detect light, chemicals and movement. One group of jellyfish, the cubozoan jellyfish, have complex eyes with lenses, corneas and retinas in their rhopalia. Although they respond to visual stimuli, scientists don’t know how the jellyfish interpret the images created by their eyes since they don’t have a brain with which to process them. Their nerve ring, a ring-shaped concentration of nerves found in jellyfish, seems to be involved, however.
Not surprisingly, given their diverse evolutionary history, jellies exhibit a fantastic range of shapes, sizes, and behaviors. When it comes to reproduction, they’re some of the most versatile creatures on the planet. Jellyfish can produce offspring both sexually and asexually; depending on the species, they may be able to create copies of themselves by dividing in two, or laying down little pods of cells, or spinning off tiny snowflake-shaped clones in a process known as strobilation. Most astonishing of all, some jellies seem able to reproduce from beyond the grave.
The so-called immortal jellyfish resembles a tiny, hairy thimble and lives in the Mediterranean Sea and also off Japan. Members of the species can reverse the aging process so that instead of expiring, they reconstitute themselves as juveniles. The juvenile then starts the jellyfish’s life cycle all over again. It’s as if a frog, say, were to revert to a tadpole or a butterfly to a caterpillar. Scientists call the near-miraculous process transdifferentiation.
The most common and widely recognized jellyfish is probably the Moon Jellyfish also known as the Common jellyfish and although it does have venom it is harmless to humans. The most a Moon jellyfish sting will do is give a very mild stinging sensation, but that is rare.
Interesting species of jellyfish
There are so many interesting species of jellyfish that exist, the biggest is the Lion’s mane jellyfish that you may find along the coast in the summer season. The Lion’s mane jellyfish is also a dangerous species that you should avoid at all costs when in the coastal water. The mane jellyfish can grow up to 2 meters wide with tentacles that are divided into eight clusters and have 150 long sting covered tentacles which what makes the lion’s mane jellyfish the biggest. The most venomous is the Australian Box jelly that can actually kill a human if they get caught in the poisonous tentacles. Then we have the most common jellyfish, the Moon jelly also known as the Aurelia Aurita, Saucer Jelly, or Common Jelly.
The most deadly jellyfish
By far the most deadly jellyfish is the Box jellyfish, specifically the Australian Box jellyfish. They are armed with tiny arrows that are full of poison and anyone or thing that gets injected with this poison may well experience paralysis, cardiac arrest, and even death, all within a few minutes of being stung.
Although the lethal varieties of the Box jelly are found mainly in the Indo-Pacific region and northern Australia. This includes the Australian Box jellyfish that are considered the most venomous of all marine animals.
Different types of Jellyfish
In the waters off North America’s West Coast lives the crystal jellyfish (Aequorea victoria), a species that is completely colorless and has long, wispy tentacles lining its glasslike bell. The remarkably gorgeous creature looks crystal clear in the daylight — hence its name — but its transparency belies a brighter side: Crystal jellyfish are actually bioluminescent, glowing green-blue when disturbed.
The upside-down jellyfish (Cassiopeia) rests its bell on the surface of the seafloor and swims with its stubby oral arms facing the sky. It does this to expose the symbiotic dinoflagellates living in its tissues to the sun, allowing them to photosynthesize, the Monterey Bay Aquarium says. The upside-down jelly is found in warm water, such as that around Florida and the Caribbean.
Flower Hat Jellyfish
you can see where the Flower Hat jellyfish gets its common name from. Seventh, on our list, these sea jellies are endemic to the Western Pacific, commonly found off the Southern Japan coast and also within the waters of Brazil and Argentina.
They tend to mostly hang about near the ocean floor among the seagrass rather than pulsing their way through the open ocean.
Although alien-like, this is a beautiful jellyfish, but don’t be fooled by the extraordinary colors of its bell that it possesses, you will know about it if it stings you as it is painful! According to the Monterey Bay Aquarium “Blooms of the flower hat jellies make swimming in coastal waters off Argentina hazardous”. The sting of this jelly is painful, leaving a bright burn like a rash. In Brazil, swarms of the Flower Hat sea jellies interfere with shrimp fishing, as they clog their nets and drive shrimp away.
The Atolla jellyfish (Coronate medusa) is widely distributed around the world. Like many other deep-sea dwellers, it has bioluminescent abilities, but it doesn’t use its bioluminescence to attract prey like the rest. Instead, it glows to deter predators.
When an Atolla jellyfish is attacked, it creates a series of flashes that attract even more predators, with hopes of them being more interested in the original attacker than the jellyfish itself. This is why the species has also been called the alarm jellyfish.
Black Sea Nettle Jellyfish
The bell of the Black Sea Nettles can reach up to three-foot across, its long tentacles reach up to 20 feet in length, and its stinging tentacles 25 feet long. Without saying, it would be pretty damn scary if you caught yourself in the middle of a bloom of these giants while in the water, but don’t worry too much as they are not that common to a lot of ocean waters.
Considering their size, which is large, this is one of the jellyfish species that are relatively new to science and we don’t actually know that much about them. It has been said that this is partly due to them being very difficult to raise in captivity and they aren’t very often discovered in the wild.
There have, however, been previous encounters where the largest blooms of Black Sea Nettles have surfaced in 1989, 1999, and in 2010. But other than these occurrences, what the largest of the jellies tend to get up to is a little bit of a mystery.
It is a hydromedusa that buds from polyps that live on the sea bottom. It does not have a large size, reaching a max of 10 cm in diameter. It is easily distinguished from other jellyfish because it has many radial canals that link the centre and the margin of the flat bell. The mouth and the manubrium are inserted in a gelatinous bulge that originates from the centre of the bell and projects downwards. From this jellyfish genus, the green fluorescent protein (GFP) was isolated from a substance that produces light in many jellyfish. The discovery of this protein allowed the development of new techniques for diagnosing pathologies and research in molecular biology. This discovery led to application in diagnostics, allowing to mark specific cell lines.
The medusa form of this jellyfish has a squarish, box-like bell, from which its name is derived. From each of the four lower corners of this hangs a short pedalium or stalk which bears one or more long, slender, hollow tentacles. The rim of the bell is folded inwards to form a shelf known as a velarium which restricts the bell’s aperture and creates a powerful jet when the bell pulsates. As a result, the box can move more rapidly than other jellyfish; speeds of up to 6 metres (20 ft) per minute have been recorded.
We hope you have learnt some interesting information on Jellyfish, they are certainly beautiful and mysterious creatures that are a sight to behold but best from a distance in some cases at least.
Watch jellyfish models swim quietly, creating a beautiful ambiance. Lifelike jellyfish movements are so realistic you will question if they are real.
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