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EXPLORING LIFE EXERCISE 9: THE ANNELIDS AND THE MOLLUSKS Exercise 9: The Annelids and the Mollusks Workbook Contents Corresponding Section on CD Vocabulary Key Concepts Introduction 1. Introduction The Animal Kingdom Characteristics of Animals Animal Cells Early Evolution of the Animals Protostomes and Deuterostomes 2. The Animal Kingdom 2A. Overview 2B. Animal Cells 2C. Early Evolution of the Animals 2D. Protostomes and Deuterostomes The Annelids Anatomy of the Earthworm The Class Polychaeta The Class Oligochaeta The Class Hirudinea 3. The Annelids 3A. Anatomy of the Earthworm 3B. The Polychaetes 3C. The Oligochaetes 3D. The Hirudinea The Mollusks The Origin and Evolution of the Mollusca and the Basic Body Parts Common Among Mollusks The Classes of the Mollusca 4. The Mollusks 4A. Origin and Evolution of Mollusks 4B. The Basic Body Plan 4C. Classes of the Mollusca Summary & Review Vocabulary Archenteron - The cavity in the gastrula which forms the embryonic gut Blastopore - The opening from the outside into the archenteron of the gastrula Blastula - The hollow ball of cells formed early in embryonic development Clitellum - The swollen, paler section of skin that produces mucus and is important in reproduction in many annelids Coelom - The cavity within the body formed by splitting of the mesoderm in protostomes and by outpocketing in the deuterostomes Determinate/indeterminate cleavage - In determinate development or cleavage, the fates of cells in terms of function and location in the adult organism are determined early in the process of development of the embryo. In indeterminate development or cleavage, cells in the early stages of embryonic development are totipotent; they can take on many different functions and locations in the adult organism. Detritus - Remaining fragments of dead organisms; dead organic matter Deuterostome - An animal whose development produces the mouth as a second opening following gastrulation; the echinoderms and chordates develop in this way Dioecious - Having separate sexes, with male and female functions occurring in separate individuals 9-1 Ectoderm - The outer layer of tissue in multicellular animals Endoderm - The inner layer of tissue in multicellular animals, forming, for example, the inner epithelium of digestive and respiratory tracts Epitoky - The occurrence of a special reproductive stage in the life cycle of some annelids Gastrula - The stage of embryonic development at which invagination of the blastula has formed a "cup-like" stage Hermaphroditic - A reproductive strategy in which both male and female reproductive structures and functions are combined in a single individual Hirudin - A substance in the saliva of leeches that prevents coagulation of blood at the site of attack in its host Integument - A covering or coating layer in an animal Lumen - The cavity of an organ Mesenchyme - The mass of tissue between the ectoderm and endoderm of a gastrula Mesoderm - The embryonic tissue layer lying between the ectoderm and endoderm; from it such things as muscles develop Metamerism - A body plan in which the body is constructed of a number of more or less similar segments Mosaic development - A pattern of development in which the fates and functions of cells in the adult organism are determined early in embryonic development Nephridia - A general term for the excretory organs of invertebrates Osphradium - A sense organ sensitive to chemicals in the environment; this form of chemosensory structure is associated with the gills of mollusks Parapodia - The paired, lateral appendages of each segment of the Polychaete body; their functions may include locomotion and gas exchange Pelagic - Inhabiting open water, usually the ocean, but the meaning has been broadened to include fresh water Periphyton - The plants and animals living on the surfaces of rooted aquatic plants Peritoneum - The membrane lining the surfaces of the body cavity, i.e., covering both internal organs and abdominal walls Pharynx - The tube forming the anterior part of the digestive tract; in some species it may be everted to capture prey Pheromone - A hormone-like chemical which affects other individuals rather than organs and tissues within the individual producing it Protandry - A reproductive strategy in which the male parts of a hermaphrodite mature and function before the female parts Protostome - an animal in which the first opening (or blastopore) of the gastrula becomes the mouth of the adult animal; annelids, mollusks, and arthropods develop in this way Pseudocoel - The space between the mesoderm of the body wall and the internal organs formed from the blastocoel of the embryo; it is not formed within the mesoderm as are the true coeloms of protostomes and deuterostomes Pygidium - The anal segment of annelids; also the terminal segment of a number of arthropods, including beetles, fleas and scale insects Rynchocoel - The most primitive form of body cavity, found in the Nemertea (ribbon worms), it forms a cavity around the proboscis Septum - A barrier separating two segments, as in the bodies of annelids Setae - The hairs or bristles extending from the lateral margins of annelid bodies, particularly important for locomotion in oligochaetes; also the hairs or bristles formed as extensions of the exocuticles of insects Sodium pump - The energy-dependent, coupled molecular pump (a membrane protein) that exchanges sodium and potassium across the cell membrane against their concentration gradients Torsion - The twisting of the gastropod body by 180 degrees during development Zygote - The diploid cell formed by the fusion of male and female gametes at fertilization 9-2 KEY CONCEPTS This section of the workbook is set up to help you note important information relating to the key concepts of this exercise and then organize and summarize the information in order to develop a synthesis and prepare for a review. As you complete this exercise, you will focus on the structural and life cycle characteristics of the animals, particularly the simple ones, so that you will be able to distinguish: What is an animal? 1. What structural and life cycle characteristics distinguish animals from all other organisms? 2. What are the evolutionary trends in development in the structural and life cycle characteristics of the animals, particularly the simple ones? How are the lower animals classified? 3. What structural and life cycle characteristics distinguish each group of animals from every other group? 4. What structural and life cycle characteristics distinguish each class of animals within a group from every other class within that group? The first twelve pages are questions that can be answered by following the progression of slides and paying careful attention to the information, both visual and audio. These questions should be read in advance of each section so that you can be better prepared to answer them by knowing what you are looking for. The underlined subheadings correspond to the sections of the exercise as outlined in the main menu. Italicized subheadings denote a series of slides within a larger section. The subsequent five pages are designed to help you summarize and synthesize the pertinent information to answer the questions posed above. 9-3 THE ANIMAL KINGDOM Introduction 1. Circle the characteristic in each group that is common to all members of the animal kingdom. You will have to listen to the audio and read the screen to complete this question. a. All animals are multicellular / unicellular. b. All animals have a cell membrane and a cell wall / a cell membrane only. c. All animals obtain nutrition by eating other organisms or their remains / photosynthesis; in other words, all animals are autotrophic / heterotrophic and do / do not have chloroplasts. 2. Match each group of animals with its type of developmental pattern: (D) deuterstomes or (P) protostomes. annelids arthropods chordates echinoderms mollusks The Animal Kingdom Characteristics of Animals 3. Label the phylogenetic tree with the following terms: ancestral protists, Parazoa, Eumetazoa, Porifera (sponges), Radiata, Ctenophores, Cnidaria, Bilateria, Protostomes, Annelids, Mollusks, Arthropods, Deuterostomes, Echinoderms, Chordates 4. List the common name(s) and one characteristic for each of the groups: a. Porifera: b. Ctenophores: c. Cnidaria: d. Annelids: e. Mollusks: f. Arthropods: g. Echinoderms: h. Chordates: 9-4 KEY CONCEPTS 5. What are the defining characteristics of each taxon that you must become familiar with? List them: a. b. c. d. e. f. g. Animal Cells 6. What are the implications of each of the differences between animal and plant cells? Describe them: a. Animal cells lack chloroplasts, so animals must survive by . Some are mobile / stationary filter feeders while others are mobile / stationary and require location. Energy consumption in animals is higher / lower than it is in plants, so animals require less / more oxygen. . b. Animal cells lack rigid cells walls, so animal cells can This permits animal bodies to be less / more flexible and makes locomotion impossible / possible. What are some animal cells that move within their bodies? List at least two and explain why their ability to move is important The absence of cell walls means that animals need another mechanism to give their bodies some . What are the three strategies that animals use for this purpose? c. The plasma membrane is important in controlling of the cell. Animal cells control osmotic pressure by means of a potassium / sodium pump. Early Evolution of the Animals 7. Describe how each animal group evolved from the ancestral protists and the characteristics of each group: a. Porifera: Body plan is / is not symmetric, they do not have / have tissues and organs, and there is great / little functional integration among cells. The sponges are the most advanced / primitive of the animals. b. Radiata: Animals in this group are bilaterally / not / radially symmetric and have one / two / three embryonic tissue layers. 9-5 THE ANIMAL KINGDOM c. Bilateria: These animals all have one / two / three embryonic tissue layers and generally exhibit bilateral / no / radial symmetry. d. Rotifera: All are large / small, most are aquatic / terrestrial, and they draw food into their mouths with cilia / flagella arranged in a structure called the . e. Nematoda: Many roundworms are free-living / parasitic in the soil while others are free-living / parasitic on other organisms. f. Nemertea: Ribbonworms are the most advanced / primitive phylum having a body cavity, called the pseudocoelom / rhynchocoel in this group. It is / is not used for movement. g. Platyhelminthes: Some flatworms are free-living / parasitic and have evolved / lost sensory structures to aid in food finding. Others have adapted to a free-living / parasitic lifestyle and have increased / reduced sensory structures. Since food is readily available, these flatworms, which include tapeworms and flukes, have increased / reduced guts, while most of the body volume is taken up with digestive / Flatworms Roundworms 9. Match each label with the correct structure on one or both diagrams of this flatworm: ectoderm – epidermis mesoderm – mesenchyme endoderm pharynx gastroventricular diverticulum 9-6 have intestinal tube have digestive sac hermaphroditic sexes separate no body cavity or coelom have body cavity called pseudocoel two tissue layers three tissue layers size and speed less restricted size and speed restricted cells obtain oxygen and remove wastes through diffusion organs for oxygen transport and waste excretion Mark an "X" under each characteristic that is found in the following groups: anus present 8. mouth present reproductive organs. KEY CONCEPTS 10. Match each label with the correct structure on one or both diagrams of these roundworms. Gender: Gender: dorsal nerve cord pseudocoel uterus ovary testis intestine longitudinal muscle layer ventral nerve cord Protostomes and Deuterostomes 11. Number each step in the developmental process, then match it with its description: Step Description zygote begins dividing, forming a solid ball of cells blastula forms, with fluid-filled cavity called blastocoel gastrulation begins; true coelom is formed within mesoderm and lined with the peritoneum archenteron forms as gastrulation continues; blastopore forms as opening to outside; three tissue layers apparent 12. Match each statement with the corresponding developmental pattern: (D) deuterostome or (P) protostome. mesoderm forms around lip of the blastopore cleavage is radial mesoderm forms from the gut wall cleavage is determinate coelom arises by outgrowth from the gut cleavage is indeterminate coelom forms by splitting mesoderm cells are initially totipotent blastopore becomes the anus mosaic development blastopore becomes the mouth regulative development cleavage is spiral have a true coelom 9-7 THE ANNELIDS AND MOLLUSKS The Annelids Anatomy of the Earthworm 13. The worms of the phylum Annelida are (circle one) flat / ribbon-like / rounded / segmented. They are bilaterally / radially symmetric and do / do not have a true coelom. 14. Match the labels with the diagrams of the earthworm: epidermis mouth brain coelom pharynx heart crop testis ovary septum dorsal blood vessel nephridium intestine ventral blood vessel ventral nerve cord segmented ganglia longitudinal muscle layer circular muscle layer setae 15. Describe how an earthworm moves. Be sure to differentiate between the functions of the circular and longitudinal muscles: EC What is the importance of segmentation (metamerism) in the evolution of animals? 9-8 KEY CONCEPTS The Class Polychaeta 16. Circle the term(s) or phrase(s) on each line that best describe the structural or lifestyle features of this class: Habitats a. mostly marine or marine and freshwater or some terrestrial Habits b. crawl along bottom or free-swimming or burrowing Anatomy c. external movement – parapodia or tentacles or suckers d. setae – many or few or none e. external sensory – eyes or antenna or palps or groups of cells (no organs) Gas Exchange f. “gills” or moist integument or hemoglobin Locomotion g. none (sessile as adults) or “rowing” or segmental contraction Feeding h. predatory or filter or suspension or deposit or scavenging or parasitic Reproduction i. dioecious or hermaphroditic j. special reproductive form: k. fertilization – internal or external The Class Oligochaeta 17. Circle the term(s) or phrase(s) on each line that best describe the structural or lifestyle features of this class: Habitats a. mostly marine or mostly freshwater or some terrestrial Habits b. crawl along bottom or free-swimming or burrowing Anatomy c. external movement – parapodia or setae or tentacles or suckers d. setae – many or few or none Locomotion e. none (sessile as adults) or “rowing” or segmental contraction f. special muscles for locomotion: Anatomy and g. internal – septa or sphincters or no separation of segments h. external – epidermal pores or no pores Gas Exchange i. “gills” or moist integument or hemoglobin Anatomy j. circulatory system – open or closed k. digestive system structures: Feeding l. predatory or filter or suspension or deposit or scavenging or parasitic Anatomy m. nervous system structures: n. external sensory – eyes or antenna or palps or groups of cells (no organs) Reproduction o. dioecious or hermaphroditic p. protandric or not protandric q. special reproductive structures: r. fertilization – internal or external 9-9 THE ANNELIDS AND MOLLUSKS The Class Hirudinea 18. Circle the term(s) or phrase(s) on each line that best describe the structural or lifestyle features of this class: Habitats a. mostly marine or marine and freshwater or some terrestrial Feeding b. predatory or filter or suspension or plant-eating or scavenging or parasitic Gas Exchange f. “gills” or moist integument or hemoglobin Anatomy c. external movement – parapodia or tentacles or suckers Reproduction d. dioecious or hermaphroditic e. special reproductive structures: Anatomy f. internal – septa or sphincters or no separation of segments or sinuses g. setae – many or few or none Locomotion h. “rowing” or segmental contraction or sucker attachment Habits b. crawl along bottom or free-swimming or burrowing Feeding i. special structures: Anatomy j. nervous system structures: Reproduction k. protandric or not protandric l. fertilization – internal or external 19. Reviewing each of the previous sections, list and describe at least two example organisms from each class: a. Polychaeta: b. Oligochaeta: c. Hirudinea: The Mollusks The Origin and Evolution of the Mollusca & the Basic Body Parts Common Among Mollusks 20. Number, in order from 1 to 5, the possible evolutionary steps of the mollusks: radula to scrape surfaces for food rapid evolution of diversity in Cambrian period spicules expanded into plates over dorsal surface spicules of calcium carbonate in dorsal surface worm-like, partially segmented ancestor 9-10 KEY CONCEPTS 21. Match each structure with its description and its location on each diagram by placing the corresponding letter in the blanks provided: A. shell contains digestive, excretory and circulatory systems B. mantle contains most sensory organs and mouth C. digestive system digests food and absorbs nutrients D. visceral mass encases gills E. head helps circulate water around gills F. gills protects body G. radula responsible for locomotion; secretes mucous H. mantle cavity scrapes food off of surfaces I. foot secretes shell 9-11 THE ANNELIDS AND MOLLUSKS 22. Number, from 1 to 11, the steps in mollusk eating and digestion. cilia draw food-mucus strings into stomach larger particles formed into fecal pellets fecal pellets are expelled through anus larger particles pass into intestines food becomes entangled in mucus from salivary glands small particles digested intracellularly food-mucus passes as strings through esophagus to stomach small particles pass into digestive gland stomach acids break down mucus strings form protostyle in stomach food scraped from surface by radula EC Describe the structure and function of the nervous system. You may include labeled diagrams. Use an additional sheet of paper if needed. 23. True or False: The mollusk shell expands by active secretion along its inside edge. True or False: The shell increases in both size and thickness simultaneously. The Classes of the Mollusca 24. Circle the term(s) or phrase(s) on each line that best describe the structure or lifestyle features of each class. You may want to work on Question #25 at the same time. Anaplacophora Taxonomy a. major class or minor class Habitats b. primarily marine or marine and freshwater or some terrestrial Anatomy c. head – distinct or indistinct, poorly developed or none d. foot – none or compressed or present or modified into tentacles e. mantle or no mantle Shell Structure f. none/embedded spicules or single valve or double valve or reduced internal Anatomy g. feeding – radula or beak Feeding h. scrape algae/herbivorous or carnivorous or scavenge or parasitic Reproduction i. hermaphroditic or dioecious 9-12 KEY CONCEPTS Question #24 continued: Monoplacophora Taxonomy a. major class or minor class Shell Structure b. none or single cap or 8 plates or tusk-like or single valve Habitats c. primarily marine or marine and freshwater or some terrestrial Anatomy d. gills – reiterated or not reiterated or replaced by lungs Reproduction e. hermaphroditic or dioecious Locomotion f. creep on foot or burrow or “jet-propelled” or sessile (none as adults) g. foot – none or compressed or present or modified into tentacles Anatomy h. anus and gills – to rear or to front Polyplacophora Taxonomy a. less than 200 species or more than 200 species Shell Structure b. none or 8 plates or single valve or double valve or reduced internal Habitats c. primarily marine or marine and freshwater or some terrestrial Anatomy d. feeding – radula or beak Feeding e. scrape algae/herbivorous or carnivorous or scavenge or parasitic Locomotion f. creep on foot or burrow or “jet-propelled” or sessile (none as adults) Anatomy g. foot – none or compressed or present or modified into tentacles h. mantle or no mantle i. head – distinct or indistinct, poorly developed or none j. eyes or no eyes Reproduction k. hermaphroditic or dioecious Anatomy l. sensory organs - well developed or limited Scaphopoda Taxonomy a. less than 200 species or more than 200 species Shell Structure b. none or tusk-like or single valve or double valve or reduced internal Habitats c. primarily marine or marine and freshwater or some terrestrial Locomotion d. creep on foot or burrow or “jet-propelled” or sessile (none as adults) Feeding e. scrape algae or grasp with tentacles or scavenge or parasitic Anatomy f. eyes or no eyes Reproduction g. hermaphroditic or dioecious 9-13 THE ANNELIDS AND MOLLUSKS Question #24 continued: Bivalvia Shell Structure a. none or single valve or double valve or reduced internal Anatomy b. foot – none or compressed or present or modified into tentacles Locomotion c. creep on foot or burrow or “jet-propelled” or sessile (none as adults) Habitats d. primarily marine or marine and freshwater or some terrestrial Feeding e. scrape algae or filter or grasp with tentacles or scavenge or parasitic Anatomy f. gills – reiterated or not reiterated or replaced by lungs g. head – distinct or indistinct, poorly developed or none h. sensory organs - well developed or limited i. mantle or no mantle j. tentacles or no tentacles Reproduction k. hermaphroditic or dioecious l. protandric or not protandric Gastropoda Taxonomy a. less than 200 species or more than 200 species Habitats b. primarily marine or marine and freshwater or some terrestrial Anatomy f. head – distinct or indistinct, poorly developed or none h. anus and gills – to rear (posterior) or to front (anterior) Shell Structure e. none or single spiral valve or double valve or reduced internal Locomotion d. creep on foot or burrow or “jet-propelled” or sessile (none as adults) g. foot – none or compressed or present or modified into tentacles Anatomy j. mantle or no mantle k. gills – reiterated or not reiterated or replaced by lungs l. sensory organs - well developed or limited m. eyes or no eyes Feeding f. herbivorous or filter or suspension or carnivorous or scavenge or parasitic Anatomy i. feeding – radula or beak Reproduction o. hermaphroditic or dioecious 9-14 KEY CONCEPTS Question #24 continued: Cephalopoda Anatomy a. head – distinct or indistinct, poorly developed or none Shell Structure b. none or single valve or double valve or reduced internal Anatomy c. foot – none or compressed or present or modified into tentacles Habitats d. primarily marine or marine and freshwater or some terrestrial Feeding e. herbivorous or grasp with tentacles/carnivorous or scavenge or parasitic Anatomy f. feeding – radula or beak Locomotion g. creep on foot or burrow or “jet-propelled” or sessile (none as adults) Anatomy h. brain – ring of ganglia or well-developed and encased i. sensory organs - well developed or limited j. eyes or no eyes 25. Review the section on mollusk classes. List and describe at least one example organism from each of the classes. a. Aplacophora: b. Monoplacophora: c. Polyplacophora: d. Scaphopoda: e. Bivalvia: f. Gastropoda: g. Cephalopoda: 9-15 SUMMARY & REVIEW 1. What are the three characteristics that unite all animals in terms of their: b. cell structure: a. structure: c. nutrition acquisition: Evolutionary Trends 2. In each group, list the characteristics of the animals in order from most primitive to most derived. The first one has been done for you as an example: a. symmetry: asymmetrical to radial symmetry to bilateral symmetry b. tissues and organs: to c. embryonic tissue layers: to d. habitats: to e. body cavity: to to f. sensory structures: to to 3. Without looking at your Key Concepts, fill in the following phylogenetic tree: 5. Write the letter of the phylum next to the appropriate common name and organism: A. Porifera comb jelly B. Cnidaria flatworm C. Ctenophora jelly fish D. Rotifera ribbon worm E. Nemertea rotifer F. Nematoda roundworm G. Platyhelminthes sponge 9-16 THE ANIMAL KINGDOM; THE ANNELIDS AND MOLLUSKS 6. Complete each statement with the appropriate word or phrase for each developmental pattern: Protostomes Deuterostomes a. mesoderm forms: b. coelem forms: c. blastopore becomes (mouth or anus): d. cleavage is (spiral or radial): e. cleavage is (determinate or indeterminate): f. development is (mosaic or regulative): 7. What is metamerism? What is its significance? With what phylum/group does this characteristic first appear? 8. What characteristics are unique to each of the phyla of “worms”? a. Nemertea: b. Nematoda: c. Platyhelminthes: d. Annelida: 9. After you fill out the table on the next page, list the characteristics that are unique to each class of Annelida: a. Polychaeta: b. Oligochaeta: c. Hirudinea: 10. What characteristic(s) do primitive mollusks share with annelids? 9-17 SUMMARY & REVIEW Habitats mostly marine mostly freshwater mostly terrestrial Habits crawl along bottom free-swimming burrowing Feeding predatory filter-feeding suspension-feeding deposit-feeding deitritus/scavenging parasitic plant-eating Locomotion none - sessile as adults "rowing" segmental contraction sucker attachment Gas Exchange "gills" moist integument hemoglobin Reproduction dioecious - sexes separate epitoky hermaphroditic but not protandric hermaphroditic and protandric clitellum albumin-filled cocoon formed external fertilization internal fertilization Anatomy External - sensory eyes antenna palps groups of cells - no organs External - movement parapodia setae - many setae - few setae - none "tentacles" sucker(s) External & internal - digestive "jaws" mouth gizzard crop pharynx proboscis salivary glands intestines nephridia anus Other external & internal septa sphincters epidermal pores cerebral ganglia segmental ganglia ventral nerve cord closed circulatory system longitudinal muscles circular muscles 9-18 Hirudinea Oligochaeta Polychaeta Hirudinea Oligochaeta Polychaeta Mark an "X" next to each characteristic that is found in all or some of the members of each of these classes. THE ANIMAL KINGDOM; THE ANNELIDS AND MOLLUSKS 11. In each group, list the characteristics of the mollusks in order from most primitive to most derived. The first one has been done for you as an example: a. taxonomy: few species to many species to b. habitats: c. shell structure: to d. head: to e. mantle: to to f. gills: to g. sensory structures: to to to to h. “brain” : 12. After you fill out the table on the next page, list the characteristics that are unique to each class of Mollusca: a. Anaplacophora: b. Monoplacophora: c. Polyplacophora: d. Scaphopoda: e. Bivalvia: f. Gastropoda: g. Cephalopoda: 13. Write the letter of the phylum next to the appropriate common name and organism: A. Polychaeta “few seta” B. Oligochaeta “head foot” C. Hirudinea leeches D. Anaplacophora “many plates”; chitons E. Monoplacophora “many seta” F. Polyplacophora “no plates” G. Scaphopoda “one plate” H. Bivalvia “stomach foot” I. Gastropoda tooth or tusk shells J. Cephalopoda “two valves” 9-19 Taxonomy minor class; under 200 species major class; over 200 species Habitats marine only or primarily marine and freshwater some terrestrial representatives Feeding scrape algae off rocks with radula filter feed grasp food with tentacles herbivorous carnivorous scavenge parasitic suspension feed Locomotion creep on foot burrow "jet-propelled" sessile (do not move as adults) Shell Structure no shell; may have imbedded spicules shell single cap from union of spicules segmented shell of 8 plates shell is cylinder or cone, tusk-like single valve shell double valve shell reduced internal shell External Anatomy distinct head no head, head indistinct or poorly developed tentacles no tentacles foot no foot or compressed foot anus and gills to rear anus and gills to front (via torsion) Internal Anatomy - Viscera radula beak mantle no mantle reiterated gills, muscles, excretory structures gills, muscles, excretory structures not reiterated gills replaced by lungs Internal Anatomy - Nervous and Sensory sensory organs limited sensory organs well developed eyes no eyes "brain" a ring of ganglia well-developed brain Reproduction hermaphroditic; may be protandric dioecious 9-20 Cephalopoda Gastropoda Bivalvia Scaphopoda Polyplacophora Monoplacophora Aplacophora Cephalopoda Gastropoda Bivalvia Scaphopoda Polyplacophora Monoplacophora Mark an "X" next to each characteristic that is found in all or some of the members of each of these classes. Aplacophora SUMMARY & REVIEW 9-21