Jelly fish or jellies are softbodied, free-swimming aquatic animals with a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate to acquire propulsion and locomotion. The tentacles may be utilized to capture prey or defend against predators by emitting toxins in a painful sting.
Jelly fish species are classified in the subphylum Medusozoa which makes up a major part of the phylum Cnidaria, although not all Medusozoa species are considered to be jellyfish.
Jellyfish are found in every ocean, from the surface to the deep sea. Scyphozoans are exclusively marine, but some hydrozoans live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. Jellyfish have roamed the seas for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal
As jellyfish squirt water from their mouths they are propelled forward. Tentacles hang down from the smooth baglike body and sting their prey. Jellyfish stings can be painful to humans and sometimes very dangerous.
The popular English name jellyfish has been in use since 1796. It has traditionally also been applied to other animals sharing a superficial resemblance, for example ctenophores (members from another phylum of common, gelatinous and generally transparent or translucent, free-swimming planktonic carnivores now known as comb jellies) were included as “jellyfishes”. Even some scientists include the phylum ctenophora when they are referring to jellyfish. Other scientists prefer to use the more all-encompassing term gelatinous zooplankton, when referring to these, together with other soft-bodied animals in the water column.
As jellyfish are not true fish, which are vertebrates, the word jellyfish is considered by some to be a misnomer. Public aquaria often use the terms jellies or sea jellies instead. The term “jellies” may have become more popular than “jellyfish”. In scientific literature, “jelly” and “jellyfish” are often used interchangeably. Some sources may use the term “jelly” to refer to organisms in this taxon, as “jellyfish” may be considered inappropriate.
Many textbooks and sources refer to only scyphozoans as “true jellyfish”.
A group of jellyfish is sometimes called a bloom or a swarm. “Bloom” is usually used for a large group of jellyfish that gather in a small area, but may also have a time component, referring to seasonal increases, or numbers beyond what was expected. Other collective names for a group of jellyfish are “fluther” and “smack,” though neither term is commonly used by scientists who study jellyfish. Jellyfish are “bloomy” by nature of their life cycles, being produced by their benthic polyps usually in the spring when sunshine and plankton increase, so they appear rather suddenly and often in large numbers, even when an ecosystem is in balance. Using “swarm” usually implies some kind of active ability to stay together, which a few species such as Aurelia, the moon jelly, demonstrate.
There’s a reason that stories of Atlantis and other lost underwater world civilizations have long captured our imaginations. The idea that an entire city could just vanish beneath the waves is a terrifying thought. While these lost underwater cities aren’t the mythical Atlantis, that’s exactly what happened to them, and their haunting remains have been documented by divers and archaeologists.
It was called Heracleion by the ancient Greeks and Thonis by the ancient Egyptians. Once situated on the northern coast of Egypt and established as one of the most important port cities of the Mediterranean, this lost underwater world city has been sitting at the bottom of the sea that it once served. Recently excavated after 1,200 years underwater, Thonis-Heracleion has been slowly giving up its secrets.
Artifacts brought to the surface indicate the ancient city was once a massive trading center and bustling port city. More than 60 ancient shipwrecks have been found in the immediate area, along with hundreds of anchors, coins from across the sea, tablets inscribed in ancient Greek and Egyptian, and vast sculptures that were thought to have once adorned the city’s temples. Those temples have also remained eerily intact, complete with offerings and votives once given to the ancient Egyptian gods.
Like many underwater cities, the conditions that the artifacts have been submerged in for centuries have preserved them incredibly well. What hasn’t been determined exactly is how the lost city ended up at the bottom of the sea, although it’s thought to have sunk after an earthquake. Built on the already precarious series of deltas reaching out into the sea, the best guess is that the already questionably stable sand and clay eventually gave way after a tremor.
The ancient city of Phanagoria is a case of fiction and mythology becoming truth. According to Roman history, an uprising in 63 BC ended with a huge part of the ancient city being burned and the wife and children of Mithradates VI being murdered by the angry mob. For years, it was thought the whole account was just a tall tale – it was completely unsubstantiated, after all.