Transcript Chapter 25
Chapter 25 Invertebrates A Summary AP Biology Spring 2011 Animals Groups Numbers Chordates Vertebrate chordates: mammals, birds, reptiles, amphibians, jawed fishes, jawless fishes Invertebrate chordates: tunicates , lancelets Vertebrates: 4500, 8600, 7000, 4900, 21000, 84 Invertebrates: 2100 Echinoderms Sea stars, sea urchins 6,000 Arthropods Crabs, spiders, insects 1,113,000 (recent estimates of 10’s of millions) Roundworms Pinworms, hookworms 22,000 Mollusks Snails, slugs, octopuses 100,000 Annelids Leeches, earthworms, polychaetes 12,000 Rotifers Bdelloids 2,000 Flatworms Turbellarians, flukes, tapeworms 20,000 Cnidarians Jellyfish, hydra 10,000 Placozoans Trichoplax adhaerens 1? Poriferans Sponges 9,000 Animals: multicelled heterotrophs that ingest other organisms or some portion of them Tissues are arranged into organs and organ systems Most motile at some stage of their life cycle They reproduce sexually, and in some cases asexually, or both Embryos develop through a series of stages Animal Origins Variation in Animal Body Plans ◦ Organization: ◦ All animals are multicellular and show an internal division of labor ◦ A key innovation for animals was development of tissues ◦ Tissue development starts in the embryo Specialized Cells, Tissues, Organs Cell: the basic unit of all forms of life ◦ A neuron is a cell Tissue: group of similar cells that performs a particular function ◦ Sciatic nerve is a tissue Organ: group of tissues that work together to perform related functions ◦ Brain is a organ Specialized Cells, Tissues, Organs Tissue Development ◦ Outer ectoderm is the tissue giving rise to the epithelium that lines the body surfaces and forms other organs, and in some species, serves as an external skeleton (ex. Insect cuticle) ◦ Endoderm develops into the gut lining and connective tissues serving as the structural material for an internal skeleton ◦ Third tissue layer forms between the other two, mesoderm, which is the source of muscles and other organs in all animals more complex than jellyfishes Germ Layers Germ Layers Diploblastic: animals with only 2 cell layers, their bodies consist of ectoderm and endoderm, and mesoglea (middle glue) holds two layers together ◦ Porifera and cnidarians Triploblastic: having 3 true cell layers ◦ Complex animal phyla Germ Layers Bilateral Symmetry: body is organized along a longitudinal axis with right and left sides that mirror each other ◦ Most are triploblastic ◦ Occurs in humans, lobsters Radial Symmetry: any cut through the central axis of the organism would produce mirror images ◦ Occurs in jellies Body Symmetry Symmetry Cephalization: concentration of sensory equipment at one end (usually the anterior, or head end) of the organism Development of Head Coelomates: posses a body cavity filled with fluid, and this space separates an animal’s digestive tract from the outer body wall ◦ A true coelom forms from tissue derived from mesoderm ◦ Most complex: Annelida, Mollusca, Arthropoda, Chordata Body Plans Pseudocoelomates: are triploblastic animals with a cavity formed from the blastocoel, rather than the mesoderm ◦ Nematodes or roundworms Acoelomates: have no cavities between their alimentary canal and the outer wall of their bodies ◦ Flatworms Body Plans Coelom: fluid filled body cavity that is completely surrounded by mesoderm tissue ◦ Represents advance in course of animal evolution because it provides a space for elaborate organ systems ◦ Like digestive tract or cardiovascular system Body Plans From the Primitive To the Complex No symmetry or radial symmetry Bilateral symmetry No head Head with sensory apparatus Mesoglea holds two cell layers together 3 cell layers, including mesoderm Acoelomate Pseudocoelomate or coelomate No true tissue True tissues, organs, and organ systems Little specialization Much specialization Sessile Motile Be familiar with 9 common phyla and representative animals of each For each animal phyla: think in terms of strategies that animals have evolved to adapt to particular environments and notice the trends of development from simple to complex Characteristics of Animals Domain Archaea Bacteria Eukarya No symmetry Have no nerve of muscle tissues Sessile- do not move Filter nutrients from water drawn into a central cavity Consist of two cell layers only: ectoderm and endoderm connected by noncellular mesoglea Porifera: Sponges Have specialized cells but no true tissues or organs, each cell carriers out many functions Evolved from colonial organisms ◦ If you squeeze a sponge through fine cheesecloth it will separate into individual cells that will spontaneously reaggregate into a sponge Reproduce asexually by fragmentation Also reproduce sexually: hermaphrodites Porifera: Sponges Radial symmetry Body plan is polyp (vase shaped), which is mostly sessile, or medusa (upside down bowl shaped), which is mostly motile Cnidarians: Hydra and Jellyfish Life cycle: some go through a planula larva (free swimming) stage then go through two reproductive stages ◦ Asexually reproducing (polyp) ◦ Sexually reproducing (medusa) Cnidarians: Hydra and Jellyfish Two cell layers only: ectoderm and endoderm connected by noncellular mesoglea Have a gastrovascular cavity where extracellular digestion occurs Carry out intracellular digestion inside body cells in lysosomes Cnidarians: Hydra and Jellyfish Have no transport system because every cell is in direct contact with the environment All members have stinging cellscnidoctes ◦ Containing stingers, which are called nematocysts Ex. Hydra Cnidarians: Hydra and Jellyfish Simplest animals with: ◦ Bilateral symmetry ◦ An anterior end and three distinct cel layers (ectoderm, endoderm, mesoderm) Platyhelminthes: Flatworms, Tapeworms Digestive cavity has only one opening for both ingestion and egestion so food cannot be processed continuously Have solid body and no room for true digestive or respiratory systems to circulate food or oxygen Flatworms have solved this problem in a unique way They body is so flat and thin that many body cells can exchange nutrients and wastes by diffusion with the environment Platyhelminthes: Flatworms, Tapeworms Unsegmented worms with bilateral symmetry but little sensory apparatus Many are parasitic ◦ Trichinella causes trichinosis, contracted by eating uncooked pork C. elegans: widely used as an animal model in studying genes and embryonic development Nematodes: Roundworms C. elegans Platyhelminthes: Flatworms, Tapeworms Bilateral symmetry with little sensory apparatus Digestive tract is a tube-within-a-tube consisting of crop, gizzard, and intestine Nephridia for excretion of nitrogen wastes, urea Closed circulatory system: heart consists of 5 pairs of aortic arches Annelids: Segmented Worms (earthworms, leeches) Blood contains hemoglobin and carries oxygen Diffusion of oxygen and carbon dioxide through moist skin Hermaphrodites Annelids: Segmented Worms (earthworms, leeches) Have soft body often produced by a hard calcium-containing shell Open circulatory system with blood-filled spaces called hemocoels or sinuses Mollusks: Squids, Octopuses, Slugs, Clams, and Snails Have bilateral symmetry with 3 body zones: ◦ Head-foot: contains both sensory and motor organs ◦ Visceral mass: contains the organs of digestion, excretion, and reproduction ◦ Mantle: specialized tissue that surrounds the visceral mass and secretes the shell Mollusks: Squids, Octopuses, Slugs, Clams, and Snails Radula: movable, tooth-bearing structure, acts like a tongue Most have gills and nephridia Mollusks: Squids, Octopuses, Slugs, Clams, and Snails Jointed appendages Segmented into head, thorax, abdomen More sensory apparatus than in annelids ◦ Gives them more speed and freedom of movement Chitinous exoskeleton protects animal and aids in movement Arthropods: Insecta (grasshopper), Crustacea (shrimp, crab), Arachnida (spider) Open circulatory system with a tubular heart and hemocoels, sinuses Malpighian tubules for removal of nitrogenous wastes, uric acid Air ducts called trachea bring air from the environment into hemocoels Arthropods: Insecta (grasshopper), Crustacea (shrimp, crab), Arachnida (spider) Most are sessile or slow moving They have bilateral symmetry as an embryo but revert to the primitive radial symmetry as an adult The radial anatomy of the adult is an adaptation to a sedentary lifestyle Echinoderms: Sea Stars (Starfish) and Sea Urchins Their water vascular system creates hydrostatic support for the tube feet, the locomotive structures Reproduce by sexual reproduction with external fertilization Echinoderms: Sea Stars (Starfish) and Sea Urchins Can reproduce by fragmentation and regenerate ◦ Any piece of a sea star that contains part of the central nervous canal will form a completely new organism Have endoskeleton consisting of calcium plates ◦ Endoskeleton grows with the body ◦ Exoskeleton does not and must be shed periodically Echinoderms: Sea Stars (Starfish) and Sea Urchins Two subphyla of invertebrate chordates Simpler versions of vertebrates Chordates: Tunicates, Lancelets Many of 4 anatomical features that characterize chordates appear only during embryonic development ◦ Notochord: long, flexible rod that appears during embryonic development between the digestive tube and the dorsal nerve cord ◦ Dorsal, hollow nerve cord: formed from a plate of ectoderm that rolls into a hollow tube Chordates: Tunicates, Lancelets ◦ Pharyngeal clefts: grooves that separate a series of pouches along the sides of the pharynx; in most chordates the clefts develop into slits that allow water to enter and exit he mouth without going through the digestive tract ◦ A muscular tail posterior to the anus Chordates: Tunicates, Lancelets Have a notochord: rod that extends the length of the body and serves as a flexible axis Have a dorsal, hollow nerve cord The tail aids in movement and balance Coccyx bone in humans is a vestige of a tail Vertebrates Chordates: Fish, Amphibians, Reptiles, Birds, Mammals Birds and mammals are hemeotherms ◦ Maintain a consistent body temperature ◦ All other chordates: fish, amphibians, and reptiles Cold blooded although some reptiles are endotherms (heat from within) and are able to raise their body temperature Chordates: Fish, Amphibians, Reptiles, Birds, Mammals