You all will be very well aware of jelly-like fishes – jellyfish. If we speak technically, jellyfish is not a fish at all. Why? Well, there are many reasons that they are not added to this family but the most genuine and easy-to-get reason is that jellyfish do not have vertebrae –cupola-shaped invertebrates and in genuine fishes’ anatomy they are vertebrates. And due to this reason, they have been added to another phylum or taxonomic group. This taxon is called Cnidaria and species in it are called Cnidarians. Biologists and anatomists would rather like to call them jellies because technically they are not fish, just jellies floating freely in the waters. Everyone has heard of them, but what are these jellies, and why do they keep floating in the water? Jellies are mushy invertebrates, associated with the taxon Cnidarians. The word Cnidaria has been taken from the Greek word “cnidos” which means stinging vex and respectively Cnidarians mean biting animals. The Cnidarians have more than 10000 species all over the world. They come in the simplest category of the higher organisms, more complex than sponges, but less complex than organisms like a fish star. Physically, the species of the Cnidarian phylum are radially uniform, resembling sea stars. It means that their bodies expand outward from the center like the spokes of a wheel of a bicycle. This phylum has a number of species including anemones, corals, jellies, and hydroids. All the Cnidarians have got tentacles that have stinging and biting cells in their nibs. They use these tentacles to capture and defeat their prey. These stinging cells are known as cnidocytes and they have a special composition in it called a nematocyst. The nematocyst is a specialized twisted very thin stinger in the tentacles of the Cnidarians that contains venom. When the nematocyst shoots, the twist is opened and directly injected straight. The arrow-like thread passes through the cell wall and prey and paralyzes it. Some Cnidarians have poison in their tentacles and they disable their prey and some have not. Most of the cnidarians are not harmful to humans because they are not able to inject nematocyst into human’s thick skin. But there are still some cnidarians however like specific jellies and hydroids that can penetrate intensely painful and sometimes even deadly bites to humans. Deep under the waters, everything has its own specific position and place. Whether they are detritus feeders on the seabed that feed on decomposed sea plants and animals and sometimes on their extraction too or the shallow waters carnivores that keep the balance of the fish population, all the underwater creatures play their role that is crucial for the marine environment. But some of them are ignored and Cnidarians are one of them. In groups, they assist to sustain the variety and solidity of the whole marine environment. They play different roles in the marine ecosystem. Sometimes they act as predators, sometimes they provide shelter to small organisms and they also act as filter feeders. Let’s get to know more about this special phylum of the marine ecosystem.

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