Imagine having no blood, no heart and no brain yet somehow managing to survive and evolve over five hundred million years. Humans wouldn’t be able to function without ONE of those vital organs, let alone surviving without having ALL of them.
Jellyfish have existed since before dinosaurs walked the earth, and with the recent changes in the climate and ocean environment, are becoming more bountiful. Plagued with overfishing and pollution the marine ecosystem is changing drastically before our very eyes. Large pelagic fish and sea turtles, are rapidly decreasing in populations and becoming endangered. This is problematic given that some of these species are natural predators to the jellyfish and keep their population in check. These undesirable changes, are bound to increase the jellyfish that populate local waterways in the near future.
As the name implies, jellyfish literally look and feel like jelly. These simplistic animals, are composed of 90% water and often times have a transparent or translucent body. A jellyfish is made up of three parts; a bell, oral arms and tentacles. The bell or hood is the main body portion which often looks like an umbrella. This hood houses all the jellyfishes simplistic organs including a nerve net (which is a basic version of our brain and nervous system), gut (the digestive-excretory system), circulatory system and osmoregulatory system (used to absorb and filter water in and out of the jellyfish’s body). The oral arms connect to the main body stalk, specifically encircling the gut in the center of the jellyfish. They help form the opening to the oral cavity where food is consumed and excreted. In case you haven’t figured it out, yes it does mean a jellyfish eats and poops from the same hole. The tentacles are the stringy spaghetti like filaments that trail behind the jellyfish and catch its prey. It is sometimes difficult to differentiate between the oral arms and tentacles and most people think they are the same thing. The biggest thing to remember is even though both appendages have the stinging potential, the oral arms encircle to the mouth/anus of the jellyfish while the tentacles are thinner and form the outer part around the bell.
As lifeless as these animals may seem in the water, floating along at the mercy of ocean currents, jellyfish do have a sense of directionality and the ability to propel themselves. Eye spots located around the outer edge of their bells enable jellyfish to sense their environment and navigate up, down and around obstacles. While not as specialized as human eyes, these light sensing organs see light and dark shadows and in box jellyfish can even go as far as seeing colour. In addition to their eyespots, jellyfish can move throughout the water column by using a combination of muscle and osmoregulation. Considered one of the most energy efficient swimmers in the animal kingdom, jellies radially expand and contract their bodies expelling jets of water behind them in order to move forward.
On top of being found in every ocean of the world, jellyfish come in a variety of shapes and sizes. One of the largest species of jellyfish is called the Lion’s Mane jelly (Cyanea capillata) with a bell measuring about 6 feet in diameter and tentacles trailing behind it up to 49 feet in length. While the Lion’s Mane jelly is one of the longest species of jellyfish on the planet, you’d be lucky if you didn’t need a microscope to see the Creeping Jelly (from the genera Staurocladia and Eleutheria). Having a tiny bell diameter measuring 0.5 millimeters and tentacles not much longer, the Creeping Jelly is considered the smallest recorded jellyfish.
While these passive animals do not purposely try to harm humans they do possess specialized cells found in their oral arms and tentacles that have the ability to sting. These stinging cells are called nematocysts and they are triggered to sting upon contact. The potency of the sting is completely species dependant. Different types of jellies have different lengths of nematocysts as well as different venom toxicity. Stings from species such as moon jellies and nettles could range from a dull tingle to a small rash, whereas brushing up against a box jellyfish could leave you in severe pain and could even result in death.
It’s not by choice that jellyfish sting us, their tentacles simply have pressure sensitive cells that are wired to sting upon contact. The best way to avoid dealing with jellyfish and the nasty punch they can pack is to pay attention and familiarize yourself with the beach you are swimming at. Listen to the news, talk to locals and pay attention to warning signs often posted at beach entrances. These signs are great indicators to any hazards in the area. Jellyfish tend to move to coastal regions in large swarms as the temperature get warmer.
Should you encounter a jellyfish while swimming, apart from taking a moment to appreciate its grace and beauty as it pulsates through the water, the best thing to do is leave it alone and move to another area.
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