ZoologyLesson 1 of 1 in the course Introduction to Animal Diversity

Animal Classification by Symmetry, Germ Layers, Body Cavities, and Development

5 flashcards · 5 quiz questions · 5 match pairs · 4 fill-in sentences · English

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Summary

Scientists classify animals using patterns in their bodies and development. This lesson focuses on body symmetry, a visible feature that helps explain how animals interact with their surroundings.

Symmetry describes how body parts are arranged around an animal’s body axis. A symmetrical animal can be divided into roughly equivalent halves along one or more planes. Symmetry is useful for classification, but it is not an absolute rule: animal groups can include exceptions and changes during development.

All flashcards

What is asymmetry in an animal?
A body arrangement that cannot be divided into equivalent halves by any plane.
What is biradial symmetry?
Radial body organization in which only a limited number of planes divide the body into equivalent halves.
What is one function of a coelom?
It cushions organs and provides space for them to grow and move.
Which animals are examples of acoelomates?
Flatworms, which lack a coelomic cavity between the gut and body wall.
How do protostomes and deuterostomes differ in the traditional blastopore model?
The mouth forms at or near the blastopore in protostomes; in deuterostomes, it forms at the opposite end.

Quiz questions

  1. In ctenophore rotational symmetry, what results from division along the oral–aboral axis?Answer: Two copies of the same half, with one rotated 180 degrees.
  2. What distinguishes a true coelom from a pseudocoelom?Answer: A true coelom is lined by mesoderm-derived epithelium.
  3. Which structures typically develop from ectoderm?Answer: The body’s outer epithelial covering and central nervous system.
  4. In determinate cleavage, what happens to a blastomere’s developmental fate?Answer: It is established early in development.
  5. Why are echinoderms classified within Bilateria despite their adult radial symmetry?Answer: They evolved from bilateral ancestors and have bilateral larvae.

Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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