ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Review Questions and Answers		AP BIOLOGY: Chapter Thirty-Nine Outline THE CLASSIFICATION OF ANIMALS Divided into Two Subkingdoms tbl 39.1 Parazoa Lack definite symmetry Neither tissues nor organs are present Consist primarily of sponges Eumetazoa Possess definite shape and symmetry Have tissues organized into organs and organ systems Include all other animals, 35 phyla Comparison of Parazoa and Eumetazoa Eumetazoa are generally more complex than sponges Eumetazoa form three distinct embryonic cell layers Outer ectoderm, inner endoderm and intermediate mesoderm Layers differentiate into tissues of the adult Sponges lack tissue layers Evolutionary relationships Derived from the same unicellular ancestor Resembled choanoflagellate protists fig 39.1 Subgrouping of Invertebrate Animals "Primitive" or "lower" invertebrates Have less complex tissue organization Comprise 14 phyla Four phyla more successful than the others Porifera = sponges Cnidaria = jelly fish + hydroids + sea anemones + corals Platyhelminthes = flatworms Nematoda = roundworms "Advanced" or "higher" invertebrates PHYLUM PORIFERA: THE SPONGES General Biology of Sponges Primarily marine species, fewer freshwater varieties fig 39.2 Few radially symmetrical, but most lack any symmetry Many are colonial, all are sessile as adults Cellular organization Little coordination among cells Simple mass of cells in a gelatinous matrix Cells are specialized for different functions Filter feeders Water flows through system of pores and canals Water forced out through a larger pore called the osculum Water forced through passageways by beating flagella Basic structure fig 39.3 Choanocytes Specialized flagellated cells that face inward Line internal cavity or specialized chambers in large sponges Epithelial layer of flattened cells, frequently contractile in nature Mesenchyme Intermediate gelatinous layer with amoeboid cells May possess minute, needles called spicules May possess fibrous spongin protein network The Choanocyte fig 39.4 Structurally resembles a protist with a single flagellum Independent beating of flagella creates water currents Used to acquire food and oxygen and expel wastes Body cavity inner wall may be convoluted to increase surface area Microstructure Base of flagellum surrounded by collar of hair-like projections Strands of collar connected by microfibrils Food particles in water filtered by collar, collected in mucus Food digested by collar cell or adjacent amoeboid cell Reproduction in Sponges Frequent reproduction by fragmentation Sexual reproduction via production of egg and sperm Larval sponges undergo development within adults Have external choanocytes when released Exist as free-swimming planktonic form for a short time Settle on a suitable substrate to begin a sessile adult life Turn inside out, choanocytes become internal PHYLUM CNIDARIA: THE CNIDARIANS Two Phyla Exhibit Radial Symmetry Throughout Life Cnidaria: hydroids, jellyfish, sea anemones and corals fig 39.4 Ctenophora: comb jellies Both are considered to be most primitive Eumetazoans Primitive since tissues not organized into organs Were widespread in Precambrian times General Biology of Phylum Cnidaria Nearly all are marine, only a few are freshwater Basically gelatinous, have tissues but no organs Carnivores, capture food with tentacles that surround mouth Exhibit two body forms fig 39.5 Polyp: cylindrical, generally attached to a substrate Solitary or colonial Mouth faces away from substrate, generally upward May form hard internal or external skeleton Medusa: umbrella-shaped, free-floating Mouth faces substrate, generally downward Possess a thick jelly-like mesoglea, between epidermis and gastrodermis May exist in polyp or medusa forms only or alternate between the two phases Both forms are diploid Reproduction Polyps reproduce asexually by budding, form polyps or medusae Sexual reproduction produces fertilized eggs Develops into a free swimming, multicellular, ciliated planula larva Evolutionary advancement: development of an internal digestive cavity Digestive enzymes secreted into a primitive gut Food broken into smaller particles Particles further digested by cells lining gut Enable cnidarians to digest food larger than individual cells Undigested food particles exit gut through mouth Gastrovascular cavity = gut = coelenteron: has only one opening Organization of tissues Nerve cells organized into nets to coordinate muscle contraction No blood vessels No respiratory system No specialized internal cavity Cnidaria possess cnidocytes Structures specialized for food capture and defense Located on tentacles, sometimes the body surface Each cnidocyte contains a harpoon-like nematocyst fig 39.6 Propelled by water pressure Protein toxin injected into prey Portuguese man-of-war possesses powerful neurotoxins fig 39.7 Stings of other jellyfish can be severely painful Symbiotic relationships of nudibranchs and flatworms Ingest nematocysts without discharge Retain nematocysts for own defense systems Classes of Cnidarians Class Hydrozoa: hydroids Have both polyp and medusa forms Mostly marine, colonial forms Example: Portuguese man-of-war fig 39.7 Example: freshwater Hydra fig 39.6 Atypical, has polyp form only Readily glides on basal disk or somersaults Class Scyphozoa: jellyfish fig 39.4b Conspicuous medusae alternate with inconspicuous polyp forms Outer layer contains contractile epitheliomuscular cells Separate male and female individuals produce planulae Class Anthozoa: sea anemones and corals fig 39.4c Solitary and colonial marine organisms Cylindrical body with tuft of tentacles in multiples of six Live primarily in shallow warm waters, harbor photosynthetic algae Exclusively polyp form Sea anemones are soft-bodied Corals secrete hard or protein skeletons that comprise coral reefs PHYLUM CTENOPHORA: THE COMB JELLIES Relationship to Cnidarians Traditionally thought to be closely related Recent research questions this assumption General Biology of the Ctenophorans fig 39.8 Transparent spherical to ribbon-shaped forms, few centimeters long More complex than Cnidaria, have anal pores Abundant in the open ocean Have two long retractable tentacles Possess eight comb-like plates of fused cilia for locomotion Many are luminescent BILATERAL SYMMETRY Comparison of Bilateral Symmetry to Radial Symmetry fig 39.9 Bilateral organisms exhibit right and left halves Possess dorsal (top) and ventral (bottom) halves Differentiate anterior (front) and posterior (back) Allows for differential adaptation of various parts of body Body Plans of Bilaterally Symmetrical Animals fig 39.10 Acoelomate: possess no body cavity other than digestive system Pseudocoelomate: body cavity develops between mesoderm, endoderm Coelomate: body cavity completely bounded by mesoderm, internal organs suspended in it by mesenteries Examples Acoelomates and pseudocoelomates are all worms Coelomates are more diverse in body form, include the vertebrates ACOELOMATES: THE SOLID WORMS fig 39.10 Phylum Platyhelminthes: The Flatworms fig 39.11 General biology Dorsoventrally flattened bodies, have definite head at anterior end Bodies are solid, gut is the only internal cavity Many species are parasitic others species are free-living carnivores or scavengers Move via ciliated epithelial cells on lower surface Organ systems of flatworms fig 39.12 Digestive system is branched with a single opening Cannot feed continuously Gut also functions to transport food Partial extracellular digestion, also phagocytosis Tapeworms lack digestive system, bathed in nutrients Excretory system of fine tubules with bulb-like flame cells Primarily regulate water balance Excretion evolved secondarily Lack a circulatory system, food and oxygen transported via diffusion Simple nervous system with longitudinal nerve cords, primitive brain Free living forms possess sensory systems on side of head Detect chemicals and fluid movements associated with food Eye spots are light sensitive, pigmented cups Generally more active than radially symmetrical invertebrates Reproductive systems are complex Most flatworms are hermaphroditic with internal fertilization Asexually reproduce by fragmentation followed by regeneration Class Turbellaria: the turbellarians Free living organisms, found in water and moist habitats Example: Dugesia, the common planarian fig 39.12 Class Trematoda: the flukes Parasitic forms have epithelium and gut linings resistant to host digestive enzymes Lack sensory and locomotive adaptations of free-living forms Take food in through mouth Have complex life cycles involving one, two or more hosts Example: Clonorchis sinensis, human liver fluke fig 39.12b Eggs containing miracidium larva passed out in feces Ingested by snail, transformed into sporocyst Sporocysts produce rediae Nonciliated redia give rise to cercariae Cercariae released in water, are free-swimming Bore into muscles of fish, turn into metacercariae Humans eat fish, cysts dissolve, flukes migrate to liver Example: Schistosoma blood flukes fig 39.13 Life cycle Eggs leave body in urine and feces, hatch into miracidia Become sporocytes which form daughter sporocytes Daughter sporocytes become cercariae, burrow into human skin Get into blood stream, go to lungs, go back to blood Male and female worms mate on way to hepatic and portal veins Adults live in blood vessels feeding intestines or bladder Shed eggs continuously for many years Disease schistosomiasis is spreading through the tropics Control via breaking life cycle Investigations into effects on immune reaction, develop vaccine Class Cestoda: tapeworms Extremely specialized parasitic organisms fig 39.14 Absorb food through outer body wall Bodies divides into scolex, neck and reproductive proglottids Proglottids formed continuously from region behind neck Eggs toward end mature, become fertilized Embryos emerge from end proglottids, leave host in feces Example: Taenia saginata, beef tapeworm (often found in humans) fig 39.14 Phylum Rhynchocoela: The Ribbon Worms fig 39.15 Mostly marine, free-living ribbon-shaped or thread-shaped worms Have a long, muscular, retractable proboscis for capturing prey Simplest organisms that possess complete digestive system Simplest animals with closed circulatory system A Body Cavity Pseudocoelomate Animals fig 39.10 Include seven phyla, Nematoda contains the most members Pseudocoel serves as a hydrostatic skeleton against which muscles contract Lack defined circulatory systems Have complete, one-way digestive tract Phylum Nematoda: Nematodes Include nematodes, eelworms and roundworms Ubiquitous and abundant in marine, freshwater and terrestrial habitats fig 39.16 Most are microscopic in size, parasitic and live in soil fig 39.17 General biology of nematodes Bilaterally symmetrical, cylindrical, unsegmented worms Covered by thick, flexible cuticle that is molted periodically Have longitudinal muscles located beneath the epidermis Pull against cuticle and pseudocoel Results in side-to-side whipping movement Specialized digestive system with piercing stylets, mouth, pharynx and anus Completely lack cilia or flagella Excretory systems of canals or glands not dependent on cilia Reproduction sexual, generally the sexes are separate Development is simple, precise Caenorhabditid elegans composed of 1000 cells Fate of each cell completely mapped out Many Nematodes Parasitize Humans Example: Trichinella, pig intestinal roundworm fig 39.18 Trichinosis may occur if pork eaten raw or undercooked Worms may also infect bears and be transmitted to humans Example: Filaria, worms living in lymphatic vessels Infection passed by mosquitos Causes gross swelling of extremities, elephantiasis Phylum Rotifera: Rotifers fig 39.19 Microscopic animals found in aquatic and soil habitats Have crown of cilia at heads for feeding and locomotion Have muscular pharynx with grinding jaws inside Have flame cells like flatworms to control osmotic pressure Sexual reproduction with separate sexes Some species possess only females and reproduce solely by parthenogenesis