RAVEN 9/e

CHAPTER 32: OVERVIEW OF ANIMAL DIVERSITY

WHERE DOES IT ALL FIT IN?

Chapter 32 takes the same strategy as Chapters 27 through 31 and highlights the diversity of animals. Students should be encouraged to recall the principles of eukaryotic cell structure and evolution associated with the particular features of animal cells. Multicellularity should also be reviewed. The information in chapter 32 does not stand alone. Students should know that animals and other organisms are interrelated and originated from a common ancestor of all living creatures on Earth.

SYNOPSIS

Animals are distinctly different from other life forms studied thus far. They are multicellular, heterotrophic, have no cell walls, move rapidly and in complex ways, are diverse in form and habitat, exhibit primarily sexual reproduction, undergo embryonic development, and have unique tissues. The animal kingdom is divided into two subkingdoms: Parazoa (beside animals) and Eumetazoa (true animals). Both are derived from the same unicellular choanoflagellate ancestor. Sponges are the most familiar parazoans; they are typically asymmetrical and lack both tissues and organs. The 35 phyla of eumetazoans possess definite shape, symmetry and tissues that are organized into organs and organ systems. The Eumetazoans are further divided into Radiata (diploblastic), animals with radial symmetry and two tissue layers of ectoderm and endoderm; and, Bilateria (triploblastic), animals with bilateral symmetry and three tissue layers of ectoderm, mesoderm, and endoderm. The bilateral animals are split further into groups based on other characteristics.

Animal phyla show five key transitions in body plan as they evolve from simple to more complex forms. First, there was the evolution of tissues from no defined tissues and organs to distinct tissues with highly specialized cells. The sponges lack tissues; all other animals possess tissues. Second, there was the evolution of symmetry-asymmetry (animals with no defined symmetry), radial symmetry (animals with body parts arranged around a central axis), and bilateral symmetry (body design in which the body has a right and left halves). Porifera, the sponges, are asymmetrical, lacking any kind of symmetry. Radiata (cnidarians and ctenophora) exhibit radial symmetry while all other animals are bilaterally symmetrical. Bilateral symmetries allows for the differential adaptation of various parts of the body. It also supports the evolution of cephalization with the localization of sensory organs at one end. The third key transition is the evolution of a body cavity. Three basic kinds of body plans evolved in the Bilateria: acoelom (no body cavity), pseudocoelom (false body cavity located between the mesoderm and endoderm), and coelom (fluid-filled true body cavity that develops entirely in the mesoderm). Acoelomates like flatworms possess no body cavity and are commonly called solid-bodied worms. Seven animal phyla are pseudocoelomates, possessing a pseudocoel, including the roundworms found in phylum Nemotoda. Most members of the animal kingdom are coelomates. The gut and other internal organs are suspended within the coelom. The advent of this type of body cavity necessitated the development of a more complex circulatory system to ensure that all organs receive oxygen and nutrients. The fourth transition separates protostome and deuterstome development. Cleavage patterns differ as the protostomes undergo spiral cleavage and the deuterstomes undergo radial cleavage. Additionally, in protostomes the blastopore becomes the mouth while in deuterostomes the blastopore becomes the anus. The evolution of segmentation is the fifth key transition. Segmentation provides for more efficient locomotion and increased protection from damage due to the replication of organs in each segment. True segmentation is found in annelids, arthropods, and chordates.

The way animals are being classified is continually being reviewed and reevaluated. The current scheme has been in existence for almost a century and has always presented problems with its simplistic either/or organization. Now, new taxonomical comparisons using molecular data, the field of molecular systematics uses unique genomic sequences to identify related groups, have come to different conclusions. Morphological characters that have traditionally been used to construct animal phylogenies—segmentation, coeloms, and jointed appendages—are not the conservative characteristics as once believed.

It is believed and agreed that the animal kingdom is monophyletic, arising from a colonial flagellated protist. Three prominent hypotheses for the origin of metazoans from protists include: (1) multinucleate hypothesis suggesting that metazoans arose from a multinuclear protist;
(2) colonial flagellate hypothesis that states that metazoans descended from colonial protists; and, (3) the polyphyletic origin hypothesis that proposes sponges evolved independently from eumetazoans. Animal diversity exploded in the Cambrian and biologists still are debating what caused this explosion. Some say it was the emergence of new body plans and innovations in mobility and hunting success. Still others say it was a build up of dissolved oxygen and minerals in oceans. A new field of “evo devo” looks at the evolutionary biology and developmental biology changes. The development of Hox genes during the Cambrian era provides a tool that can produce rapid changes in body plans.

LEARNING OUTCOMES

32.1 Some General Features of Animals

  • Identify three features that characterize all animals and three that characterize only some types of animals.

32.2 Evolution of the Animal Body Plan

  • Differentiate between a pseudocoelom and a coelom.
  • Explain the difference between protostomes and deuterostomes.
  • Describe the advantages of segmentation.

32.3 The Classification of Animals

  • List the major criteria scientists have used to distinguish animal phyla.
  • Distinguish between spiralian and ecdysozoan organisms.
  • Identify the placement of humans among the animal phyla.

32.4 The Roots of the Animal Tree of Life

  • Explain the colonial flagellate hypothesis of metazoan origin and why it is now favored.
  • Describe the possible role of Hox genes in the Cambrian explosion.

COMMON STUDENT MISCONCEPTIONS

There is ample evidence in the educational literature that student misconceptions of information will inhibit the learning of concepts related to the misinformation. The following concepts covered in Chapter 32 are commonly the subject of student misconceptions. This information on “bioliteracy” was collected from faculty and the science education literature.

  • Students do not understand the evolution of endosymbionts in animal cells
  • Students are unsure that many of the lower animals are classified as animals
  • Students think that all animals evolved at about the same time
  • Students believe that all animals are mobile
  • Students believe that most animals are vertebrates
  • Students believe that animals exclusively reproduce sexually
  • Students do not equate humans with being animals
  • Students believe that cells of protists and animals are almost identical in structure and function
  • Students that animal classification is based on one linear line of evolution
  • Students believe that all animals have identical organ system structures
  • Students are unaware of molecular methods of animal classification

INSTRUCTIONAL STRATEGY PRESENTATION ASSISTANCE

Suggest that your students prepare charts indicating how various physiological functions occur in each of the phyla presented in this and the next few chapters. Include nervous activities, reproduction, respiration, digestion, excretion, circulation, and locomotion. This type of chart makes it easier to see the functional and evolutionary relationships among the various phyla.

HIGHER LEVEL ASSESSMENT

Higher level assessment measures a student’s ability to use terms and concepts learned from the lecture and the textbook. A complete understanding of biology content provides students with the tools to synthesize new hypotheses and knowledge using the facts they have learned. The following table provides examples of assessing a student’s ability to apply, analyze, synthesize, and evaluate information from Chapter 32.

Application /
  • Have students describe similarities and differences between the metabolic needs of animals and plants.
  • Have students explain if mobility is a necessary criterion for categorizing an organism as an animal.
  • Ask students to explain the benefits and negative aspects of bilateral symmetry.

Analysis /
  • Have students describe the pros and cons of using anatomical features to classify animals.
  • Have students debate whether highly conserved DNA or highly variable DNA is best for distinguishing differences between two species of animals within the same genus.
  • Ask students to explain the evidence supporting that metazoans were derived from colonial protists.

Synthesis /
  • Ask students explain how hox gene mutations that produce limb variation in animals can be used as a model for human birth defects.
  • Have students find an agricultural application for a chemical that regulates segmentation genes in animals.
  • Ask the students to find a medical application that exploits indeterminate development in deuterostome embryos.

Evaluation /
  • Ask students evaluate the benefits and risks of using research animals to study human disease.
  • Ask students to evaluate the accuracy of studying echinoderm embryos as a way of better understanding human development.
  • Ask students to evaluate the effectiveness and safety of any veterinary treatment used to kill pathogenic worms that live in pets.

VISUAL RESOURCES

Have specimens on hand of all phyla—pictures are o.k., but actual specimens of corals, anemones, hydra, sea stars, flatworms, roundworms, segmented worms, and various arthropods are necessary for the student to see the diversity in form between all animals. Most students are not familiar with the appearance of a real sponge, not even a spongin skeleton. They are only familiar with the multicolored “Pseudospongia plastica.” Bring in examples and/or photographs of others, especially finger sponges and freshwater Spongilla.

Recommend a trip to a nearby marine aquarium if possible.

IN-CLASS CONCEPTUAL DEMONSTRATIONS

A. A Remote Demonstration.

Introduction

Few students realize that researcher modern animal behavior studies are done using remote cameras that can measure animal movement, body temperature, and other physiological parameters. This demonstration permits the class to see live video-cameras animal study in which a series of cameras can be controlled by the instructor.

Materials

  • Computer with Media Player and Internet access
  • LCD hooked up to computer
  • Web browser linked to Racerocks.com at

Procedure & Inquiry

  1. Ask the class why it is preferable for researchers to study animals in nature and without disturbing the animals.
  2. Then explain you want to see a model experiment using videocams to study animal behavior and habitats.
  3. Load up the website and click on one of the videocams.
  4. Then use the controls to scan the environment and the class to hypothesize the location of the area and any obvious habitats.
  5. Then ask the class to determine the animals being studied in the camera views. Also ask them to think about any other animals that can be the subject of study by the cameras.
  6. Start the first.
  7. Ask the students briefly explain the types of information that can be gathered using the videocams to record the animal.
  8. Let the students know that the information is saved in video databases and assessed with statistical that calculates various things going on with the animals.

LABORATORY IDEAS

A. Brine Shrimp as a Toxicology Model

This activity has students design an experiment in which use brine shrimp amoebocytes (white blood cells) as a model of animal toxicology.

  1. Explain to students how animals and animal cells are used in medicine and research as models for human studies.
  2. Tell students that they will be investigating the conditions needed for fungal spore germination in two types of fungi.
  3. Provide students with the following materials
  4. Large brine shrimp in chilled water
  5. Microscope
  6. Microscope slides
  7. Plastic pipette
  8. 0.5% Trypan Blue solution in dropper bottle
  9. Sharp scalpel
  10. Standard Cytotoxic Solution of household bleach in a dropper
  11. Test solutions with droppers
  12. Endotoxins (agar or solution from Gram – bacterial colony)
  13. Pesticide
  14. 70% Ethanol
  15. Sterile water
  16. Solutions students may request if available
  17. Instruct students how to collect amoebocytes form the tail of a brine shrimp:
  18. Place the cooled shrimp on a slide with minimum amount of water
  19. Carefully slice off the tail at the base of the shrimps body
  20. Quickly place the shrimp on the microscope and focus on the cut area under medium to high power.
  21. Add 2 drops of trypan blue.
  22. Observe the amoebocytes which are small ovoid cells that leak out with the blood.
  23. Healthy amoebocytes are clear and show some cytoplasmic granules.
  24. Dying and dead amoebocytes turn blue as they take up the trypan blue.
  25. Have the students use the bleach as a cytotoxicity control to kill the amoebocytes. This is done by adding on drop of bleach to the cells in the trypan blue while observing the amoebocytes under the microcope. Have them notice how the dying and dead shrimp cells and amoebocytes turn blue.
  26. Then tell the students to test the other materials and make conclusions about their results.

LEARNING THROUGH SERVICE

Service learning is a strategy of teaching, learning and reflective assessment that merges the academic curriculum with meaningful community service. As a teaching methodology, it falls under the category of experiential education. It is a way students can carry out volunteer projects in the community for public agencies, nonprofit agencies, civic groups, charitable organizations, and governmental organizations. It encourages critical thinking and reinforces many of the concepts learned in a course.

  1. Have students do a lesson do a hands-on program on the diversity of animals at a nature center.
  2. Have students tutor high school students animal diversity.
  3. Have students volunteer on environmental restoration projects with a local conservation group.
  4. Have students volunteer at the educational center of a zoo or marine park.