Biology Homework Chapter 18: Invertebrates - Sponges to Annelids
Textbook assignment: Chapter 18: The Evolution of Invertebrate Diversity, sections 1-16
This chapter takes us on a brief survey of the different phyla of invertebrate animals.
- 18.1 The chief distinguishing characteristics of an animal are its multicellular structure (not protists or bacteria) and the fact that it gets food by ingestion (not a plant or fungi). It has a life cycle that begins with the fusion of gametes formed by meiosis into a zygote cell, which multiplies to form a blastula, continues multiplying to form first a blastula (sphere), then a gastrula (folded sphere) and three layers of tissue: mesoderm, ectoderm, and endoderm. Animals may undergo several forms (larva, nymph/pupa) prior to maturity as an adult capable of making gametes.
- 18.2 According to evolution theory, modern animal cells more closely resemble the cells of protists than bacteria. Fossil evidence indicates an increase in animal diversity in the Cambrian period, about half a billion years ago. Two major groups of animals formed: those with and those without a backbone (vertebrate).
- 18.3 Different body structures develop from the three primary layers of tissue, endoderm, mesoderm, and ectoderm; their development leads to radial or bilateral symmetry around a simple digestive tube (no coelom), a cavity partially lined with mesoderm (pseudocoelom), or a fully lined cavity (true coelom).
- 18.4 The body plans of invertebrates are used to classify them in a way that reflects their assumed evolutionary relationships. Symmetry is an important characteristic in determining how closely related different animal groups may be. Specialized tissues are also used to identify similarities between organisms and create phylogenetic trees which are used to show the most likely line of descent for diverse animals from common ancestors.
For each of the following invertebrate phyla, concentrate on the main characteristics of the phyla with respect to the major body systems and functions (digestion, nervous/brain, circulation, respiration, reproduction) and be able to compare them to one another.
- 18.5 Sponges: radial or asymmetrical, hollow cavities, specialized cells ( choanocytes and amoebocytes) but no specialized tissues or organs, suspension feeders, reproduce sexually and by budding.
- 18.6 Cnidarians : radial symmetry with medusa and polyp forms, stinging cells (cnidocytes) on tentacles, hydrostatic skeletons (hydra), hard skeletons (corals); simple digestive system, neural nets, reproduce sexually and by budding.
- 18.7 Flatworms: bilateral symmetry, aquatic, free-living (flatworms) and parasitic species (tapeworms, flukes); simple sense organs and circulation systems, but complex life cycles.
- 18.8 Nematodes (Roundworms): bilateral symmetry, pseudocoelom; complete digestive system; cuticle for protection.
- 18.9 Mollusks or molluscs (both spellings acceptible): bilateral symmetry, complete digestive system with radula used to scrape food; true circulatory system, coelom, internal organs protected in viseral mass by mantle (can be shell); cephalopods lack shell, have large brains and developed eyes.
- 18.10 Annelids or segmented worms: bilateral, segmented, closed circulatory system; three major groups: earthworms, polychaetes, leeches.
Read the following weblecture before chat: The Evolution of Animal Diversity, focussing on organisms that lack a coelom or have a pseudocoelom
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Explore the One Zoom Tree of Life, and identify the main branches. How are eukaryotic cellular life forms broken into groups here? What distinguishing characteristics are used to separate the different groups? How is this system different from the one in your text?
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- No quiz yet: the Chapter Quiz opens when we finish the chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
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