Cnidarians and their characteristics lesson for kids: 1st, 2nd, 3rd, 4th, 5th, 6th and 7th grades biology lesson.
Cnidarians (nahy-dair-ee-an) are water-dwelling animals that have lots of stinging tentacles surrounding their mouths. Jellyfish, anemone, hydra, and corals are part of this group of animals. They live in the sea, in rivers, and even in lakes.
They might seem to be very different, but all cnidarians have the same basic body structure. No part of their body can be called a “head” (they don’t even have brains!), but they all have a single opening that does the of both the mouth. It’s not just a mouth, though; after digestion, they release waste through the same opening. Cnidarians use their tentacles to catch food and push it into their mouths. Their tentacles have stinging cells that they use to inject venom into through harpoon-like projections. This helps them catch food like small fish or plankton, or helps protect them from other animals that would try to eat them.
Not all cnidarians are only dependent on eating for food, though. Some, like corals and hydras, have algae in their bodies that provide them with energy they need to live while the cnidarians provide the algae with protection and nutrients.
Cnidarians can be split into two body shapes: medusae (singular: medusa) and polyps. A medusa is another name for a jellyfish. They swim through the water by squeezing their domes, pushing against the water. Polyps can’t swim, though. They stick to the sea floor with their mouth end sticking out and their tentacles floating around, looking for food. Anemones are one example of polyps.
Most polyps reproduce can reproduce by budding, in which baby polyps grow from the body of the parent. These babies are genetically identical the parent polyps (meaning, they have exactly the same genetic code) because no other parent provided genetic information to make these babies. Some, though, combine their genes with other polyps to make new babies that each have a combination of both parents’ DNA.
You might think that medusae and polyps will always be different species of animals, but some cnidarian species are both medusae and polyps at different parts of their life cycles. Jellyfish have these complicated life cycles. They start as tiny larvae (singular: larva) that swim around until they find a good place to settle down and grow. Once they’ve found the right place, they keep growing into their polyp forms. Then, they break apart, sometimes into lots of jellyfish that have their own larvae to start the cycle all over again. Not all cnidarians go from polyp to medusa, though. Corals, anemones, and hydras don’t have medusa form.
There are so many different types of cnidarians that we can’t go through them all here, but they are all amazing animals.