1. What Is an Invertebrate?
Invertebrates are animals that have no backbone, or vertebral column.
Invertebrates make up over 95% of all animal species.
They include sea stars, worms, jellyfishes, and insects.
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2. 26-2 Sponges Photo Credit: Fred McConnaughey/Photo Researchers, Inc.
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3. What is a Sponge? What is a Sponge?
Sponges are the simplest and most ancient animals
in the phylum Porifera which means “pore-bearers.”
live their entire adult life as sessile organisms; attached to a single spot.
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4. Form and Function in Sponges
Body Plan
Sponges are asymmetrical; they have no front or back ends, no left or right sides.
Sponges carry out basic functions, such as feeding and circulation, by moving water through their bodies.
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6. Form and Function in Sponges
Feeding
Sponges are filter feeders.
As water moves through the sponge, food particles are trapped and engulfed by choanocytes that line the body cavity.
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7. Form and Function in Sponges
Circulation
Sponges rely on movement of water through their bodies to carry out body functions.
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9. Branching Tube Sponge

10. Stove Pipe Sponge

11. Vase Sponges

12. Barrel Sponges

13. Ball Sponges

14. Rope Sponges

18. 26-3 Cnidarians
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19. What is a Cnidarian? What is a Cnidarian?
Cnidarians are soft-bodied, carnivorous animals that have stinging tentacles arranged in circles around their mouths.
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20. Form and Function in Cnidarians
Body symmetry
Cnidarians are radially symmetrical. They have a central mouth surrounded by numerous tentacles that extend outward from the body.
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21. Form and Function in Cnidarians
Feeding
A cnidarian pulls its food through its mouth and into its gastrovascular cavity, a digestive chamber with one opening.
Food enters and wastes leave the body through that same opening.
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22. Form and Function in Cnidarians
Circulation
Following digestion, nutrients are usually transported throughout the body by diffusion.
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23. Portuguese man-of-war
Colonial Hydrozoan (not a single organism
Tentacles sting prey such as fish & humans
Polyps in colony feed
Has gas-filled air float
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24. Anthozoans
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25. Hydra Feeding
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26. Food in Gastrovascular Cavity
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27. Scyphozoans
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28. Some Jellyfish Show Luminescence28 28

29. 29 29

30. 27–1 Flatworms
Photo Credit: ©Carolina Biological Supply Company/Phototake
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31. What Is a Flatworm?
Flatworms are acoelomates, which means they have no coelom.
A coelom is a fluid-filled body cavity that is lined with tissue derived from mesoderm.
The digestive cavity is the only body cavity in a flatworm.
Flatworms have bilateral symmetry.
Flatworms are the simplest animals to have 3 embryonic germ layers
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32. Form and Function in Flatworms
Feeding 
Flatworms have a digestive cavity with a single opening through which both food and wastes pass.
Near the mouth is a muscular tube called a pharynx.
Flatworms extend the pharynx out of the mouth. The pharynx then pumps food into the digestive cavity.
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33. Form and Function in Flatworms
Circulation 
Flatworms do not need a circulatory system to transport materials they rely on diffusion
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35. Tapeworm Anatomy

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38. 27–2 Roundworms
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39. Roundworms
Roundworms

40. What Is a Roundworm?
Roundworms are unsegmented worms that have pseudocoeloms and digestive systems with two openings—a mouth and an anus.
Roundworms have bilateral symmetry.
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41. Form and Function in Roundworms
Feeding
Many free-living roundworms use grasping mouthparts and spines to catch and eat other small animals.
There are a variety of parasitic roundworms as well
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42. Form and Function in Roundworms
Circulation
They depend on diffusion to carry nutrients and waste through their bodies.
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44. Cysts in Contaminated Pork

45. 27-3 Annelids
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46. What Is an Annelid? What Is an Annelid?
Annelids are worms with segmented bodies. They have a true coelom that is lined with tissue derived from mesoderm.
Annelids have bilateral symmetry.
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47. Form and Function in Annelids
Feeding and Digestion
In carnivorous species, the pharynx usually holds two or more sharp jaws that are used to attack prey.
Annelids that feed on decaying vegetation have a pharynx covered with sticky mucus.
Other annelids obtain nutrients by filter feeding.
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48. Form and Function in Annelids
Circulation 
Annelids typically have a closed circulatory system, in which blood is contained within a network of blood vessels.
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