Parazoa: Definition and Characteristics

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  • 0:03 Sub-Kingdom Parazoa
  • 1:20 Characteristics of Parazoans
  • 2:56 Lesson Summary
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Lesson Transcript
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.

The sub-kingdom Parazoa is a special group of animals that are unlike any other. In this video lesson, you'll learn about the characteristics of Parazoans and identify what makes them a unique section of the Animal Kingdom.

Sub-Kingdom Parazoa

Can you imagine your life without sponges? We use them to wash dishes, clean countertops, and scrub our bodies in the shower. The sponges we use today are synthetic - they are created in factories from plastics and other materials. But before they were manufactured in mass quantities, people used to use real sponges for these very same purposes - and some people still do!

And what you may find most amazing is that sponges are in the animal kingdom! That's right, even though it may not make a very good pet, sponges are, in fact, considered animals.

Specifically, sponges make up the sub-kingdom Parazoa and the phylum Porifera. Porifera sounds an awful lot like 'pore,' doesn't it? And sponges sure do have a lot of these, so this name is quite fitting!

Parazoa are very special because they lack true tissues, otherwise known as specialized tissues. Specialized tissues are just what they sound like - each has a specific job that it is specially designed for. These may include such complex tissues as muscles and nerves, or they may be as simple as inner and outer layers of skin.

Alas, sponges have none of these. Because they lack specialized tissues, they are considered the simplest animals. But this doesn't mean that they're not interesting!

Characteristics of Parazoans

Most sponges are marine, but there are some freshwater sponges that enjoy their water without salt. Sponges come in a variety of shapes, colors, and sizes, too.

Most sponges do not have any type of symmetry, but some are radially symmetrical, meaning that they are symmetrical outward from a central point.

In general, sponges have two layers of cells that are separated by a sort of squishy area. There are cells called choanocytes on the inner layer of tissues, and these move water through the sponge's body. Sponges also have amoebocytes, which make supportive fibers in the middle body region. The sponge has a large open cavity inside called the spongocoel, which is where the water flows into. It exits the sponge at the top, through an opening called an osculum.

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