Do Cnidaria Have Germ Layers?

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Like other animals, cnidarians have germ layers that develop into different tissues of the body. In this lesson you'll learn about the different germ layers of the animals in phylum Cnidaria.

What are Cnidarians?

Have you ever been to an aquarium? What's your favorite type of animal to visit there? Many people enjoy crowding into the section with the cnidarians, mostly because these tanks contain the jellies! But phylum Cnidaria also holds some other popular players, like corals, anemones, and hydras. And while they all look different, there are quite a few similarities that lump these guys together in this classification.

Cnidaria is a diverse and beautiful phylum.
jellyfish

First, all cnidarians have radial symmetry. This is when the body is the same on all sides -- like the spokes of a wheel. They also exist in one of two forms, either the sessile polyp or the free-swimming medusa. They are also carnivores, which means that they eat other animals, and they often use their cnidocytes, or stinging cells, to capture their prey.

Cnidarians also have another thing in common - they have two germ layers. But what the heck is a germ layer? Well, these are the layers of tissue that develop from embryonic cells. They develop during a process called gastrulation, and in most animals either two or three germ layers will be present.

Cnidarian Germ Layers

In the case of cnidarians there are two layers: the endoderm and the ectoderm. The endoderm is the inner layer ('endo' for 'within'), and the ectoderm is the outer layer ('ecto' for 'outer'). If there was a third layer it would be called the mesoderm, 'meso' for 'middle'. But cnidarians do not have this middle layer.

Germ layers develop during gastrulation.
gastrulation of dipoblast

In cnidarians, the endoderm will form the internal tissues and structures such as the gastrodermis and gastrovascular cavity called the coelenteron. This is where many important processes occur for the animal, such as digestion and gas and nutrient exchange. On the outside of the animal, the ectoderm will form the tissue layer called the epidermis. Both the inner and outer layers have muscle-like fibers that help the animal move.

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