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Unit 2

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Lesson Plan 7

Concepts/Objectives | Vocabulary/Background | Activity | Extension


Lesson Plan 7




Body plan: the overall organization of an animal's body.
Invertebrate: an animal that does not have a backbone.
Phylum: animals grouped together by their similar body plans.
Segmented: animal whose body is divided into distinct sections so that it looks jointed, such as a centipede.
Tentacle: slender, finger-like extension usually found near an animal's mouth or head used to catch and handle food.


are animals that do not have backbones. Over 90% of all the animals on the earth are invertebrates! There are thousands of types of invertebrates to be seen along the shores and in the ocean off Southern California.

Scientists group all animals according to the similarities in their body plan. A body plan is the overall organization of an animal's body: what it looks like; what kind of internal and external parts it has and where they are located; how it moves and feeds. A group of animals with a similar body plan is called a phylum. Organisms within a phylum have a shared evolutionary history as well, meaning they are "related" to one another through a distant common ancestor. Invertebrates are so diverse that they include dozens of phyla (plural). In contrast, vertebrates, animals with backbones, are only a small subgroup within one phylum.

Most commonly seen invertebrates belong to one of these six phyla. If an animal belongs to one phylum, it does not belong to any other phyla.

6 Major Invertebrate Phyla:

  1. Porifera (por IF er ah) - sponges
  2. Cnidaria (ny DARE ee ah) - sea anemones and jellyfish
  3. Mollusca (mall US kah) - snails, slugs, squids and octopuses
  4. Annelida (a NELL i dah) - segmented worms (repeated body segments)
  5. Arthropoda (are thro POE dah) - insects, shrimps, lobsters and crabs
  6. Echinodermata (ee ky no der MAH tah) - sea stars, urchins, brittle stars

We can learn to recognize all these different groups by the similarities in their body plans.