ZoologyLesson 2 of 3 in the course Invertebrates

Lophotrochozoan Body Plans and the Biology of Flatworms, Rotifers, and Nemerteans

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

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Summary

This lesson introduces the shared developmental and structural features of Lophotrochozoa. Understanding these features helps explain how flatworms, rotifers, and nemerteans relate to other animal groups.

Lophotrochozoans are triploblastic animals: their embryos form three germ layers. The outer ectoderm contributes to the body surface and nervous tissues, the inner endoderm gives rise to the digestive-system lining, and the middle mesoderm forms many muscles and internal tissues. The mesoderm lies between ectoderm and endoderm, distinguishing these animals from diploblastic cnidarians.

All flashcards

What are the three embryonic germ layers?
Ectoderm is outermost, endoderm is innermost, and mesoderm lies between them.
What makes a coelom a true coelom?
It is completely lined by mesoderm, including parietal and visceral layers.
How does the digestive cavity of most flatworms function?
Its single opening serves for both food intake and digestive-waste expulsion.
What is planarian regeneration?
The ability of some planarians to regrow body regions lost through injury.
What is haplodiploidy in many rotifers?
Fertilized eggs develop into females, while unfertilized eggs develop into males.

Quiz questions

  1. How do tapeworms obtain nutrients from their hosts?Answer: They absorb already-digested nutrients through their body surface.
  2. Which description best fits the typical monogenean life cycle?Answer: A free-swimming larva attaches to one host and develops into an adult.
  3. What is the main feeding role of the rotifer mastax?Answer: Its muscular, jaw-equipped structure grinds or crushes food.
  4. Where is the nemertean proboscis housed when it is retracted?Answer: In the fluid-filled rhynchocoel above the gut.
  5. What type of circulatory system do nemerteans have?Answer: A closed system formed by connected lateral blood vessels.

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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