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Unit 4 - Phylums Platyhelminthes and Nematoda Flatworms and Roundworms Phylum Platyhelminthes • Largest group of acoelomate (no body cavity) worms • Flatworms with middle tissue layer- mesoderm • Tissues organized into organs • Bilaterally symmetrical and flat • Cells lie close to exterior enabling efficient diffusion of oxygen and carbon dioxide • Highly branched gastrovascular cavity runs close to all tissues giving cells ready access to food • No respiratory or circulatory systems Coelom – Body Cavity • The coelom usually performs multiple functions, including one or more of the following: Provides room for organ development Surfaces for diffusion of gases, nutrients, and wastes Storage Hydrostatic support Phylum Platyhelmithes • Flatworms – Liver Flukes, Planaria and tapeworms – Marine flatworms – Characteristics: • • • • • • • Ribbon-like bodies Bilateral symmetry Branched digestive system No skeleton Asexual (fission); Hermaphrodites (sexual) Free movement Skin breathing Phylum Platyhelminthes • Class Turbellaria – Most free-living; marine • Dugesia- Freshwater planarians – Digestion- Nutrients absorbed by intestinal wall and waste goes out through mouth • Muscular pharynx comes out of central mouth to feed Phylum Platyhelminthes • Reproduction- Mostly asexual by attaching posterior end to stationary object and pulling into two • Hermaphrodites can reproduce sexually • Nervous system: Brain, two nerve cords, and light-sensitive eye spots • Water balance- Water continually enters by osmosis • Flame cells with cilia draw water to the outside Phylum Platyhelminthes • Marine flatworm Phylum Platyhelminthes Planarian Phylum Platyhelminthes • Many parasitic – Endoparasite- internal – Ectoparasite- external • Class Cestoidea • Subclass Eucestoda- Parasitic flatworms (tapeworms) – Suckers and hooks on scolex (head) attach to walls of intestines and food absorbed from host’s intestines directly through the tapeworm’s skin Phylum Platyhelminthes • String of rectangular body sections (proglottids) • Each proglottid is a reproductive unit • Added continually through life • May grow up to 12 m (40 ft.) long Phylum Platyhelminthes • Most occur in vertebrates • Dozen types in humans • Taenia saginata- Beef tapeworm – Live in cow muscles in cysts – High temp. kills larvae – Subclass Cestodaria • Body not subdidvided into proglottids • Larvae in crustaceans; adults in fish Scolex Examples Phylum Platyhelmithes Proglottid – reproductive structure Phylum Platyhelminthes • Largest flatworm class, Trematoda – Parasitic worms called flukes – Endoparasites or ectoparasites • Subclass Aspidogastrea (Aspidobothrea)- Endoparasite of mollusks • Subclass Digenea- Endoparasites of vertebrates Phylum Platyhelminthes • Tegument- thick protective covering prevents them from being digested • Take nourishment directly from hosts • Use suckers to attach and the muscular pharynx to suck nourishment from host’s body fluids Phylum Platyhelminthes • Complex life cycles involve more than one host • Ex: Schistosoma- Responsible for schistosomiasis • From contaminated water • Larvae bore into host skin into blood vessels of intestines • Block vessels causing bleeding and damage to liver • Snail is intermediate host Phylum Platyhelminthes • Class Monogenea – – Monogenetic flukes – One life cycle in one host – Mostly ectoparasites on vertebrates Phylum Platyhelminthes • Liver fluke Phylum Nematoda • Roundworms- have a pseudocoelom (body cavity between endoderm & mesoderm) – Fluid movement serves as circulatory and gas exchange system – Fluid also distributes nutrients to cells from digestive system Phylum Nematoda • • • • Long, cylindrical bodies Majority microscopic and free-living One-way digestive system Thick, flexible epidermis protects and gives shape • Layer of muscle underneath pulls at epidermis and pseudocoelem for whip-like movement Phylum Nematoda • Roundworms – Ascaris, Trichinella and hookworms – Characteristics: • • • • • • • Flattened bodies Bilateral symmetry Many are parasites Fluid-filled body cavity called a pseudocoelem Digestive tube No skeleton Sexual reproduction (Internal fertilization) – Sperm is amoeboid • Free movement • Skin breathing Phylum Nematoda • Class Secernentea (Phasmidea)- Phasmids (sensory structures) in tail – Ascaris, Enterobius, Rhabditis, Turbutrix, Necator, and Wuchereria • Class Adenophorea (Aphasmidia)- No phasmids – Dioctophyme, Trichinella, Trichuris • 50 species are parasitic • Plant parasites feed on living plant cells in all parts of plant, causing wilting and withering • 14 species affect humans – Ex: Enterobius (pinworms), Ascaris lumbricoides, Trichinella spiralis, Necator (hookworms) Phylum Nematoda • Trichinella infects pigs and causes trichinosis (serious disease caused by eating undercooked pork) • Necator live in warm, moist soils of the tropics – Hookworm larvae enter bloodstream through soles of feet Phylum Nematoda • Ascaris – Carried in human waste – After ingestion, eggs hatch into larvae in intestines – Larvae bore through blood vessels, enter blood stream and then lungs (causes respiratory distress) – Larvae may enter gallbladder or pancreas causing blockages – Return to intestines to mature and mate – May grow up to 1 ft. in length Phylum Nematoda • Ascaris • Trichinella Trichinosis • Trichinella spiralis is found in pork • Trichinosis is a disease caused by the Trichinella worm. – Eggs hatch in the host’s gut – Symptoms: • • • • Diarrhea Fever Muscle pain Death Common Parasitic Roundworms • Pinworms- most common • Heartworms- transmitted to dogs by mosquitos • Filarial worms- live in blood where they block blood vessels or lymph vessels causing severe swelling (Elephantitis) • Guinea worm- Ingested with contaminated water – Cause dracunculiasis – Only found when exiting skin – Found in Africa, India and Pakistan • Hookworms attach to the inside of the digestive tract • Often found in pets