Jellyfish Facts

Jellyfish are the most abundant denizens of the marine waters. They are found in oceans across the planet, from the coldest freezing waters of the Arctic oceans to the warm, temperate waters of the tropical oceans. The article provides information regarding different interesting and fascinating jellyfish facts.

Jellyfish are among the most intimidating and intriguing creatures of the marine world. They are found across the oceans of the globe, in different water conditions and at different depths from the ocean floor to the surface, and a few species even thrive in freshwater lakes and rivers. Interestingly, jellyfish are not fish at all — they are plankton, with little or no swimming skill, mostly floating along in the direction of the ocean current, though they are capable of vertical movement. Over 2,000 species have been identified to date (some estimates run past ten thousand), and more are expected as man continues to explore the depths of the ocean. On land these curious creatures appear like jelly-like shapeless blobs, but in water they are dangerous, graceful and elusive.

Jellyfish, along with corals, sea anemones and the Portuguese Man-o-War, belong to the phylum Cnidaria and class Scyphozoa — Cnidaria coming from the Greek for ‘stinging nettle’ and Scyphozoa from the Greek for ‘cup’. Some well-known ones are the ‘Lion’s Mane’ (which featured in a Sherlock Holmes tale), and the Box Jellyfish and Irukandji Jellyfish, the last two being the deadliest, with stings that can be fatal.

Interesting Facts About Jellyfish

• Jellyfish have existed for more than 650 million years and are among the oldest living creatures on the planet — they existed before the dinosaurs and have survived longer than them.
• The jellyfish body lacks any skeletal structure and is a gelatinous substance that is about 95–98% water; only a small fraction is solid matter, so the body is soft and easily damaged. Some are tiny, while others grow seven feet across or more, with tentacles that can stretch 100 feet or longer, and can weigh over 450 pounds.
• Aquatic surroundings are vital: out of water the body collapses and the animal dies almost immediately.
• Jellyfish exhibit perfect radial symmetry — halve one from any side and the two halves are equal. This lets it detect food and respond to danger from every direction.
• Jellyfish have no blood, brain or nervous system. They possess a simple neural net and eye spots capable of sensing light from dark and reacting to gravity, while chemosensory pits help them identify food and prey.
• Jellyfish are carnivorous, feeding on crustaceans, zooplankton, tiny fish and larvae, which they trap with their tentacles while floating; the sting paralyzes or kills the prey.

Body of the Jellyfish

The body is usually transparent and gelatinous, shaped like a cup or bell and nearly filled with water. It has an outer epidermis covering, an inner gastrodermis lining, and, between the two, a jelly filling called mesoglea. A multipurpose gastrovascular cavity combines the functions of gullet, stomach and intestine, and its single orifice doubles as both mouth and anus. The orifice is surrounded by tentacles carrying sensory nerves. Jellyfish come in many colors and brightnesses — light and deep blue, yellow, purple, lilac, orange-red — and some glow in dark waters, looking rather beautiful from afar.

The Jellyfish Sting

Getting too close is not a good idea. The tentacles carry a number of capsule-like structures — the nematocysts within cells called cnidoblasts — filled with toxins. When the tentacles lash out, stinging threads inject venom into the prey or attacker, causing paralysis. In humans a serious sting can cause days or weeks of severe pain, and some species can trigger extreme reactions and even death. One comforting fact: jellyfish sold for consumption are venom-free, processed in salt and alum to neutralize the toxins and prevent rotting. Jellyfish venom is also being studied in medical research — it may help produce antidotes against other venoms and aid the treatment of cancer and other diseases.

Reproduction of Jellyfish

Adult jellyfish, called medusae, are either male or female. After the gonads produce eggs and sperm, the male releases sperm from its orifice; these swim into the female’s orifice and fertilize the eggs. On hatching, the resulting planula attaches to rocks or other solid surfaces on the sea floor and turns into a flower-like polyp, which later develops into a jellyfish.

Jellyfish as Food, and Their Enemies

Jellyfish are eaten by predators such as banner fish, sun fish, spade fish, loggerhead turtles and arrow crabs — and by human beings, jellyfish salad being a delicacy in Japan and China. Jellyfish has no flavor of its own: cooked, it takes on the flavor of the soy sauce or vinegar, and in salads it absorbs the other ingredients’ flavors. The cannonball jellyfish (Stomolophus meleagris), being larger and more rigid, is the most popular in dishes, and its nutritional content makes it a healthy snack.

Jellyfish population has increased drastically, causing problems along the coast: the number of people stung has risen sharply, and large swarms — sometimes billions strong — clog the water inlets of ships, which must be cleared of masses of dead jellyfish for the vessels to operate efficiently. Decreased rainfall raises water salinity and favors a thriving jellyfish population, and the disappearance of the animals that once preyed on them has fueled an explosion in numbers around Japan, Australia and parts of Europe. A booming jellyfish population is a sign of an upset marine ecosystem — the effects of global warming are seen here too, and this grave indicator should not be ignored.