The Reproduction of Cnidarians

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  • 0:05 What is a Cnidarian?
  • 0:53 Sexual Reproduction
  • 2:18 Asexual Reproduction
  • 3:26 Lesson Summary
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Lesson Transcript
Instructor: Heather Pier

Heather has taught high school and college science courses, and has a master's degree in geography-climatology.

Learn about the reproductive system of cnidarians, a phylum of aquatic animals that possess stinging cells. Common cnidarians include sea anemones, corals, and jellyfish. Both sexual and asexual reproduction are possible, depending on the species.

What's a Cnidarian?

If you made a list of all the crazy-sounding science words, cnidarian would certainly make the cut. Unless you know what a cnidocyte is, you probably have no idea what cnidarian might mean. Members of the phylum Cnidaria are aquatic animals (almost all live in saltwater environments) that contain cnidocytes, which are a special type of stinging cell. These stinging cells can be used for both protection and for capturing food.

Some of the most famous ocean invertebrates, including coral, jellyfish, and sea anemones, are all cnidarians. Depending on the species, the organism may be either sessile, meaning they are fixed to the ocean floor like corals, or a medusa, meaning they are free to swim like jellyfish.

Sexual Reproduction

Just as it may be hard to picture what a cnidarian is, it's also hard to imagine how they might reproduce. Both sexual and asexual reproduction are possible in cnidarians, but we will focus on sexual reproduction first because it is the most involved of the two processes.

There are many different types of cnidarians, each with a unique body structure, but the general reproductive process is the same. Male and female members of a species release their sperm and eggs into the water column. These spawning events are usually triggered by outside factors like moon phases, tides, and water temperature changes. In the water column, sperm and egg meet and fertilization occurs.

What forms from this fertilization is referred to as larva. The larva then seeks out a happy place to live as a sessile organism while it completes its growth cycle. Some species, particularly the jellyfish, will also experience what is known as an alternation of generations, in which they split themselves into two during their sessile growth phase. This is essentially an asexual reproductive event that takes place in an otherwise sexual reproductive cycle.

After growing and maturing, the young adult cnidarian then releases itself from the sea floor (unless it is to be a sessile creature like corals and anemones) to become a free swimming medusa-form adult.

Asexual Reproduction

When it comes to cnidarians, asexual reproduction might be an easier process for us to picture. All species of cnidarian are able to reproduce this way, both for reproductive purposes as well as to regenerate lost body parts. This is similar to how a starfish is able to replace a lost limb.

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