Name: ______Date: ______Period: ______
CNIDARIANS
Section 33-2: Cnidaria
Read the passage below, which covers topics from your textbook. Answer the questions that follow.
Tiny freshwater hydra, stinging jellyfish, and flowerlike coral all belong to the phylum Cnidaria. Animals in this phylum are called cnidarians. The body of a cnidarian may be either bell-shaped or vase-shaped. The bell-shaped medusa is specialized for swimming. In contrast, the vase-shaped form, called a polyp, is specialized for a sessile existence.
All cnidarians have bodies constructed of two cell layers—an outer epidermis and an inner gastrodermis. Between these layers is a jellylike material known as mesoglea. In the center of the body is a hollow gut called the gastrovascular cavity, which has a single opening, or mouth. Surrounding the mouth are numerous flexible extensions called tentacles.
Read each question and write your answer in the space provided.
SKILL:Recognizing Similarities and Differences
1.How are all cnidarians alike?
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2.What effect do the body plans of a polyp and a medusa have on movement?
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3.What body structures are common among cnidarians?
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4.The diagram shows the two body forms of cnidarians. Complete the diagram by inserting the following labels: “Epidermis,” “Gastrodermis,” “Gastrovascular cavity,” “Medusa,” “Mesoglea,” “Mouth,” “Polyp,” and “Tentacle.”
Read the question and write your answer in the space provided.
SKILL:Vocabulary Development
5.What is the meaning of the term sessile in the passage?
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Circle the letter of the word that best completes the sentence.
6.All of the following are classified as cnidarians EXCEPT
a.crayfish.
b.hydra.
c.jellyfish.
d.coral.
VOCABULARY REVIEWDistinguish between the terms in each of the following pairs of terms.
1.polyp, medusa______
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2.epidermis, gastrodermis______
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3.mesoglea, planula______
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4.cnidocyte, nematocyst______
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MULTIPLE CHOICEWrite the correct letter in the blank.
_____1.Cnidarians and ctenophores are more complex than sponges because, unlike sponges, they have
a.tissues and organs.c.a skeleton.
b.both asexual and sexual d.a backbone.
reproduction.
_____2.The structure that coordinates the complex activities of a cnidarian’s body is the
a.gastrovascular cavity. c. nerve net.
b.colloblast. d. tentacle.
_____3.An example of a cnidarian in the class Hydrozoa is a
a.coral. c. jellyfish.
b.sea anemone. d. Portuguese man-of-war.
_____4.Corals exist in a symbiotic relationship with
a.fungi.b.algae. c. hydras.d.mosses.
SHORT ANSWERAnswer the questions in the space provided.
1. How are nematocysts adapted for capturing prey?______
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2. List three differences between hydras and most other hydrozoans. ______
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3. What is the dominant body form in the life cycle of a scyphozoan? ______
What is the dominant body form in the life cycle of an anthozoan? ______
4. Describe two examples of symbiosis found among cnidarians. ______
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5. How do coral polyps produce a coral reef?______
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6. Critical Thinking Would you expect to find green hydras in a cave pond that receives little or no light? Explain your reasoning.
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STRUCTURES AND FUNCTIONSIdentify the structures labeled a–f in the diagram of a cnidarian body shown below.
Which body form is represented by this diagram?______
Original content Copyright © by Holt, Rinehart and Winston. Additions and changes to the original content are the responsibility of the instructor.
Modern BiologyCnidaria and Ctenophora