Transcript pharynx
Animal Evolution – The Invertebrates Characteristics of Animals • • • • • Multicelled heterotrophic eukaryotes Require O2 for respiration Sexual & perhaps asexual reproduction Motile at some stage Develop from embryos Here’s Something New:Symmetry! Radial Bilateral The Gut • Region where food is digested and then absorbed • Saclike gut – One opening for taking in food and expelling waste • Complete digestive system – Opening at both ends; mouth and anus Body Cavities – Acoelomate (no coelom) epidermis gut cavity no body cavity; region between gut and body wall packed with organs Body Cavities – Pseudocoel (false coelom) epidermis gut cavity unlined body cavity (pseudocoel) around gut Body Cavities - Coelom gut cavity lined body cavity (coelom) peritoneum Segmentation • Repeating series of body units • Units may or may not be similar to one another • Earthworms - segments appear similar • Insects - segments may be fused and/or have specialized functions Animal Origins • Originated during the Precambrian (1.2 billion - 670 million years ago) • From what? Two hypotheses: – Multinucleated ciliate became compartmentalized – Cells in a colonial flagellate became specialized Sponges • No symmetry • No tissues • No organs • Reproduce sexually • Microscopic swimming-larval stage • Only animals that produce nematocysts (stinging cells) Cnidarians (jellyfish) After triggering, nematocyst pierces prey • Nerve net • Hydrostatic skeleton • Saclike gut Nematocyst before triggering Flatworms • Acoelomate, bilateral, cephalized animals • All have simple or complex organ systems • Most are hermaphrodites Three Classes Turbellarians (planarians) pharynx Flukes Tapeworms Annelids • Segmented worms • Have digestive, nervous, excretory, and circulatory systems Polychaetes (Bristleworms) • Most are marine • Bristles extend from paired, fleshy parapods on each segment • Head end is specialized Leeches • Predators and parasites • Less obvious body segmentation • Most have sharp jaws Mollusks • Bilateral, soft-bodied coelomate • Most have a shell • Mantle drapes over body and secretes shell • Most have a fleshy foot • Many have a radula for shredding food Molluscan Diversity • Gastropods • Bivalves • Cephalopods Cephalopods • Only the nautilus retains external shell • Other cephalopods are streamlined, active swimmers • All move by jet propulsion – Water is forced out of mantle cavity through a funnel-shaped siphon • Have large brains relative to body size Cuttlefish Body Plan • Closed circulatory system with heart and accessory heart digestive gland radula stomach brain shell reproductive siphon accessory anus heart organ Roundworms • False coelom • Complete digestive system pharynx intestine false coelom eggs in uterus gonad anus muscularized body wall Arthropods • The phylum with the greatest number of species • Four lineages: – Trilobites (all extinct) – Crustaceans (crabs, shrimps, barnacles) – Chelicerates (spiders, mites, scorpions) – Uniramians (insects, centipedes, millipedes) Adaptations for Success • Hardened exoskeleton • Jointed appendages • Fused and modified segments • Respiratory structures • Specialized sensory structures • Division of labor Crustaceans • Most are marine, some freshwater, a few terrestrial • Head has two pairs of antenna, three pairs of food-handling appendages Copepods Crayfish Barnacles Lobsters Shrimps Crabs Isopods (pillbugs) Crab Life Cycle Larval and juvenile stages molt repeatedly and grow in size Chelicerates • Originated in seas • A few are still marine: horseshoe crabs, sea spiders • The arachnids are all terrestrial Spiders Mites Scorpions Chiggers “Daddy longlegs” Ticks Insect Diversity • Insects are the only winged invertebrates • There are more than 800,000 known species • Most successful species are small in size and have a great reproductive capacity Insect Body Plan • Thorax usually has three pairs of legs and one or two pairs of wings • Abdomen contains most internal organs and specialized structure for reproduction • Three-part gut • Malpighian tubules attach to midgut and serve in elimination of wastes Insect Headparts Butterfly Mosquito Grasshopper antenna labrum mandible Fly maxilla palps labium Types of Insect Development Growth and molting egg young adult Incomplete metamorphosis egg nymphs adult Complete metamorphosis egg larvae adult Echinoderms • Deuterostomes • Almost all are marine • Body wall has spines or plates of calcium carbonate • No brain • Adults are radial with bilateral features Echinoderm Diversity • Crinoids (sea lilies and feather stars) • Sea stars • Brittle stars • Sea urchins, heart urchins, sand dollars • Sea cucumbers Water Vascular System: Sea Star part of the water-vascular system sieve plate ring canal ampulla Animal Evolution – The Vertebrates Chapter 23 Chordates • Most are coelomate, bilateral animals • All share four features: – Notochord supports body – Nervous system develops from dorsal nerve cord – Embryos have pharynx with slits – Embryos have tail that extends past anus Lancelet Body Plan DORSAL, TUBULAR NERVE CORD NOTOCHORD PHARYNX WITH GILL SLITS TAIL EXTENDING PAST ANUS Invertebrate Chordates • Many of the animals that preceded vertebrates were like the simplest chordates – the urochordates – Sea squirts – Other tunicates Larval Form of a Sea Squirt nerve cord gut notochord oral opening (water in) Adult Tunicate atrial opening (water out) pharynx with gill slits Cephalochordates • Lancelets • Fish-shaped filter feeders that lie buried in sediments • Chordate characteristics of adult: – Notochord lies under dorsal nerve cord – Pharynx has gill slits – Tail extends past anus Hagfish Body Plan tentacles gill slits (twelve pairs) mucus glands Trends in the Evolution of Vertebrates • Shift from notochord to vertebral column • Nerve cord expanded into brain • Evolution of jaws • Paired fins evolved, gave rise to limbs • Gills evolved, gave rise to lungs Craniates • Cranium is a chamber of cartilage or bone that encloses all or part of a brain • First craniates evolved by 530 million years ago Evolution of Jaws • First fishes lacked jaws supporting structures for gill slits gill slits • Jaws are modifications of jaw, derived from support structure the anterior gill spiracle (modified gill slit) jaw support supports jaw Evolution of Fishes cartilaginous ray-finned lobe-finned fishes fishes fishes tunicates lancelets hagfishes lampreys lungfishes amphibians amniotes tetrapods jawed vertebrates vertebrates ancestral chordates craniates lungs or swim bladder “reptiles” birds mammals Jawed Fishes • Most diverse and numerous group of vertebrates • Two classes: – Cartilaginous fishes – Bony fishes Cartilaginous Fishes • Most are marine predators • Cartilaginous skeleton • Main groups: – Skates and rays – Sharks – Chimaeras (ratfishes) Bony Fishes • Includes 96 percent dorsal fins caudal fin pectoral fin (pair) of living fish species • Three subclasses: anal fin pelvic fin (pair) – Ray-finned fishes – Lobe-finned fishes – Lung fishes