Hello my fellow curious critters and welcome back to The Friendly Neighborhood Shark Lady! Today we are continuing a little series I like to call, “How Are You Even Alive?!”. In this series we learn about creatures that, quite honestly, just shouldn’t be able to exist! For example, if I were to tell you that there is an animal roaming around out there with no brain, no heart, and no blood would you believe me? 'Cause I know if I didn’t know any better, I would say I was crazy! Nature is a weird and wonderful place where an animal with no brain, no heart, and no blood does indeed exist, and it is called the jellyfish. So, let’s dive right in and learn all about how jellyfish are even alive.
So, what makes a jellyfish a jellyfish? First off, they aren’t actually fish, so it’s more accurate to call them jellies instead. There are approximately 200 different species of “true jellies,” which are animals that are part of the cnidarian (the “c” is silent) phylum (a phylum is a category used in taxonomy to group different animals together that are related evolutionarily). There are other species that are commonly called jellies, which are extremely similar in both appearance and behavior, but are not in the cnidarian phylum. Jellies are basically a gelatinous umbrella blob with dangling tentacles covered in cnidocytes (again, the “c” is silent), also sometimes called nematocysts, which are their little stingers. The tentacles surround a central mouth that opens up to a simple stomach. The mouth is also used to excrete any waste produced by the jelly. The gelatinous umbrella blob is surrounded by simple sensory organs which are used to detect light, gravity, and different chemicals found in the water.
Jellies can be found all over the world, from the arctic waters at the poles to the tropical waters near the equator. In fact, some species can even be found in freshwater systems! You can also find them at practically any depth from the surface to just above the ocean floor. They are predators typically feeding on fish, crustaceans, zooplankton, fish eggs, and larvae.
These guys are a very diverse group coming in a wide range of sizes, colors, and shapes. Their lifespans range from just a few hours as a free-swimming adult to several years. Jellies can even reproduce in a variety of ways both sexually and asexually! Sexual reproduction involves the combination of male and female gametes, or reproductive cells, after they are released into the water. When reproducing asexually, the jellies basically make a genetic clone of themselves. They can do this in a couple of different ways. In some cases, they simply divide themselves in two, while in others they release little snowflake shaped polyps that are genetic clones of themselves in a process called strobilation.
So, if they have no brain, how are they alive? How do they respond to the world around them? How do they catch their food? While they have no brain, they do have a very simple nervous system called a nerve net. These nerves allow them to respond to stimuli around them. So, if a fish swam by one of their tentacles, their nerves would fire and trigger them to release their cnidocytes, stunning the fish. The tentacles then curl up and bring the fish, or whatever prey they happened to catch, to their mouth.
Thank you so much for coming over and learning with me today! I’ve gotta admit, while sharks will ALWAYS be my favorite animals, I also really love jellies. They are just so beautiful and calming to watch. The Monterey Bay Aquarium has a fantastic live jelly cam if, like me, you find yourself needing a bit of calm in your day (here is the link: https://www.montereybayaquarium.org/animals/live-cams/jelly-cam). What surprised you the most about jellies? Let me know below! I’ll see you all back here Friday for another fin-tastic Finn Friday!
Sources:
Comments