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Ch. 30 - An Introduction to Animals
Freeman - Biological Science 8th Edition
Freeman8th EditionBiological ScienceISBN: 9780138276263Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoFreeman 8th EditionCh. 30 - An Introduction to AnimalsProblema 4
Capitolo 30, Problema 4

Which of these characteristics does not apply to cnidarians?
a. Are diploblastic
b. Possess a gastrovascular cavity with one opening
c. Undergo metamorphosis
d. Have a central nervous system

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Understand the characteristics of cnidarians: Cnidarians are a group of animals that include jellyfish, corals, and sea anemones. They are known for their radial symmetry, diploblastic tissue organization (having two germ layers: ectoderm and endoderm), and a gastrovascular cavity with a single opening that serves as both mouth and anus.
Review the term 'diploblastic': Diploblastic organisms develop from two primary germ layers during embryonic development. This is a defining feature of cnidarians, so option 'a' applies to them.
Examine the gastrovascular cavity: Cnidarians possess a gastrovascular cavity with one opening, which is used for both ingestion and excretion. This characteristic matches option 'b'.
Analyze metamorphosis: Some cnidarians, such as jellyfish, undergo metamorphosis during their life cycle, transitioning from a polyp stage to a medusa stage. This means option 'c' applies to them.
Consider the central nervous system: Cnidarians do not have a central nervous system. Instead, they have a decentralized nerve net that coordinates their movements and responses. Therefore, option 'd' does not apply to cnidarians.

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Cnidarian Characteristics

Cnidarians are a group of animals that include jellyfish, corals, and sea anemones. They are characterized by their radial symmetry, presence of specialized cells called cnidocytes for capturing prey, and a simple body plan that includes a gastrovascular cavity. This cavity serves both digestive and circulatory functions, allowing for the distribution of nutrients throughout the organism.
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Diploblastic Organization

Diploblastic organisms, like cnidarians, develop from two primary germ layers: the ectoderm and endoderm. This contrasts with triploblastic organisms, which have a third layer called the mesoderm. The diploblastic structure contributes to the simpler body organization of cnidarians, influencing their physiological functions and overall morphology.
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Nervous System in Cnidarians

Cnidarians possess a decentralized nerve net rather than a central nervous system. This nerve net allows for basic responses to environmental stimuli, but it lacks the complexity found in organisms with a central nervous system. As a result, cnidarians do not exhibit behaviors associated with higher nervous systems, such as learning or complex movement patterns.
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To estimate the relative abundance of the major phyla, calculate how many named species of arthropods, mollusks, and nematode worms exist per named species of chordate (the phylum containing vertebrates, including humans; see Table 30.1).

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