Jellyfish are free-swimming marine animals consisting of an umbrella-shaped bell and trailing tentacles. They are made of a jelly-like material. There are many types, including the stinging kinds and the non-stinging kinds called the comb jellies. In some parts of the world, millions of Jellyfish swarm together as a bloom and cause problems for fishermen and people on the beaches.
All About The Jellyfish
Jellyfish are free-swimming aquatic creatures that consist of an umbrella-shaped bell and trailing tentacles.
Jellyfish have an umbrella shaped bell and trailing tentacles
Facts About Jellyfish
Jellyfish are not very strong swimmers and depend on ocean currents for movement. Blooms often form when two currents meet and if there is an onshore breeze, thousands of jellyfish can get swept off to the beaches.
Each species has its own lifecycle. The most familiar stage is the medusa stage, where it swims and has tentacles hanging down. Male and female medusae reproduce and form thousands of larvae, named the planulae. These drift down and settle on the bottom of the ocean and form a small polyp that appears like a sea anemone. Each polyp in turn will bud off many tiny jellies called ephyrae that grow quickly into the adult stage. A single jellyfish can release as many as 45,000 eggs each day.
Jellyfish feed on small aquatic plants, crustaceans, fish eggs and larvae. Some of them even eat other jellyfish.
The stinging types have millions of small stinging cells in their tentacles called nematocysts that are used to capture food by injecting the toxin into the prey.
They provide habitat for many small fishes in areas where there is no place to hide and also protect them from predators with their stinging cells. Many young crabs hitchhike on top of them, so they don't have to swim. They are food for large fish and turtles.
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Jellyfish are made of water and protein
Jellyfish A Fascinating Underwater Creature
I was surprised to find out that jellyfish have been on earth for millions of years. Some of them have had a diameter of around 8 feet that makes them larger than a human while others are pinhead sized floating structures.
They do not have gills but breathe through their skin, so technically they are not fish but just sea jellies.
Inside the bell-shaped body is an opening that has its mouth. They eat and discard waste from it. They digest food very quickly, as they would not be able to float if they carry a large undigested meal.
Most of them do not have a specialized digestive, nervous, osmoregulatory or circulatory system. They employ a loose network of nerves called the nerve net located in the epidermis or the outermost layer of skin. A sea jelly detects various stimuli including the touch of other animals via this nerve net, which then transmits impulses to other nerve cells.
Some varieties of jellyfish have ocelli, the light-sensitive organs that do not form images but can detect light, and are used to determine up from down, responding to sunlight shining on the water surface, while a box jellyfish has 24 eyes providing it a 360 degrees view of its environment.
Depending on its species, it is made of 95-98% water and the rest is protein.
The jellyfish have limited control over their movements but can use their hydrostatic skeleton to navigate through contraction pulsations of the body. They are able to better survive in nutrient rich oxygen-poor water so that they can feast on plankton without competition.
The sting of Box jellies can be poisonous, with a survival period of only 3 minutes. They do not purposely sting humans, most of which occur accidentally when people touch a jellyfish. Vinegar (3-10% acetic acid) is a common remedy to help with jellyfish stings, but not with that of Portuguese man o' war which is not a true jellyfish. Salt water may be used as an alternative in circumstances when vinegar is unavailable.
Formation of jellyfish blooms depends on ocean currents, nutrients, sunshine, temperature, season, prey availability, reduced predation and oxygen concentration.
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