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Phylum Nematoda The Roundworms Phylum Nematoda (Greek - Nema = Thread and Eidos = form ) • • • • • • • • • • The roundworms Widespread – aquatic, marine, soil, plant parasites, animal parasites >25,000 spp. Pseudocoelomate – muscle tissue only found along external body wall; not surrounding digestive tract Bilateral symmetry Complete digestive system Cuticle – external covering, shed periodically for protection Cylindrical and tapered on both ends Dioecious (most species) No circulatory system; transport through fluid in pseudocoelom 1 • Many nematodes are important members of the soil community - decomposers • Many are important parasites – Plant parasites – Animal parasites (including – Humans!) • Following images taken from: – http://www.biosci.ohio-state.edu/~parasite/home.html Ascaris lumbricoides • Human Intestinal Roundworm 2 Necator americanus • American Hookworm • Common in So. USA • Wear shoes!!!! Wucheria bancrofti • Elephantiasis • Life cycle may be completed in host • Transmission of disease by vector – mosquito • Adults live in Lymph nodes and can prevent flow of lymph; blockage and edema 3 • Global distribution, except Europe • Only common in Tropics • >1,000,000 humans affected Dracunculus medinensis • “The fiery serpent” or Guinea Worm • Int. Host – Aquatic copepod 4 Loa loa • African eyeworm • Int. host – deer fly Trichinella spiralis • Trichina worm • Trichinosis • Very common in swine 5 Enterobius vermicularis • • • Human pinworm Direct life cycle Most common human parasite Dirofillaria immitis • Canine heartworm • Very common • Vectormosquito 6 The Coelomate Protostomes Remember: • Coelomate- body cavity completely lined with mesoderm tissue • Protostome – first opening (blastophore) becomes the mouth • Spiral cleavage • Schizocoelous – coelom forms from splits in the mesoderm tissue 7 Three major Phyla of Coelomate Protostomes • Phylum Mollusca • Phylum Annelida • Phylum Arthropoda Phylum Mollusca Latin molluscus = soft • Approx. 93,000 extant spp. • Most are marine, but also some aquatic and terrestrial forms as well • Major characteristics: – Soft body protected by dorsal shell (in most) of calcium carbonate – Most are dioecious 8 (major characteristics cont.) – Three main body parts: • Ventral, muscular foot – locomotion • Visceral mass – contains most internal organs • Mantle – fold of tissue that drapes over visceral mass and secretes shell (if present) – Radula present in many for feeding – All but one group have an open circulatory system The Chitons • • • • Marine Dorsal shell with 8 plates Ventral foot used for locomotion and to create suction Reduced cephalization 9 Gastropods – snails, slugs and nudibranchs • Marine, aquatic and terrestrial • Body asymmetric (due to torsion during embryonic development to create a better center of gravity while carrying the heavy shell) • Ventral foot used for locomotion • Shell, if present, coiled or flat (torsion – rotation of visceral mass) 10 The Bivalves • • • • • • clams, oysters, mussels and scallops Marine and aquatic Flat shell, opens ventrally; hinged dorsally Mantle forms incurrent and excurrent siphons (two valves) Reduced cephalization Foot for locomotion by digging Powerful adductor muscles for shell closing 11 The cephalopods – squid, octopus, chambered nautilus (with external shell) • • • • Marine Foot divided into tentacles with suction cups Active predators; using a modified siphon to provide jet propulsion Only mollusk with a closed circulatory system (higher metabolic rates) • ADVANCED NERVOUS SYSTEM – capable of learning and more complex behaviors (I.e. communication), very well developed sense organs • Giant squids are the world’s largest invertebrate (>15m in length) 12 Phylum Annelida (little rings; annulus=ring) • Evolutionary landmark – metamerism = repetition of body segments • Metamerism provides the evolutionary opportunity to specialize body segments • Coelomate protstomes • Bilateral symmetry • Metanephridia for excretion of metabolic wastes and osmoregulation • Approx 16,500 spp. • Found in all habitats on earth – marine, aquatic, terrestrial • In general, most annelids are cylindrical “worm-shaped”, segmented animals 13 Earthworm • Lumbricus terrestris • Important ecologically in soil community • Anatomy of earthworm – Monoecious • Reproductive segments –clitellum Anatomy of earthworm continued • Setae • Digestive system – – – – – – – Mouth Anus Pharynx Esophagus Crop Gizzard Intestine 14 Polychaete worms • well developed head; many seta present on parapodia; • Nereis – polychaete worm or sandworm and Christmas tree worms Leeches Anterior and posterior suckers Ectoparasites Hirudin - anticoagulant 15 Phylum Arthropoda (arthros=joint + pod=foot) • Main characteristics of phylum arthropoda – Coelomate protostomes – Bilateral symmetry – Jointed appendages (legs, antennae, reproductive appendages, mouth or feeding appendages) – Ectoskeleton (exoskeleton) from ectoderm; must be shed periodically (molt = ecdysis); made of chitin – Segmented body divided into three regions (tagma = body division) • Head • Thorax • Abdomen Phylum Arthropoda (arthros=joint + pod=foot) • Main characteristics of phylum arthropoda – Open circulatory system – Respiratory organs • Tracheal tubes – opening called spiracles • Gills • Book lungs – Very diverse group - > 1,000,000 spp. (mostly insects) – Most successful animal phyla – colonize all habitats – 2 out of 3 living things on earth is an arthropod 16 • The earliest arthropods are thought to have been trilobites (extinct) – Pronounced segmentation but little differentiation between body segments Arachnids • Spiders, scorpions, mites and horseshoe crabs • Body divided into two or three tagma • Six pair of appendages – Chelicerae – Pedipalps – 4 pair of walking legs 17 18 • The horseshoe crab (Limulus) • Crustaceans – – – – – Shrimp, crabs, crayfish, lobsters and barnacles Cheilpeds (pinchers) Biramous appendages Carapace covers cephalothorax Swimming appendages – uropod, swimmerets 19 – Barnacles • Myriapods • millipedes and centipedes – Two pair of walking legs per segment – Uniramous appendages – terrestrial 20 centipedes – one pair of walking legs per segment – Uniramous appendages – terrestrial Hexapods – Insects • • • • Most diverse class of animals Six pair of walking legs Two pair (usually) of wings !!!! Metamorphic life cycle – Incomplete metamorphosis – Complete metamorphosis 21 22