ch. 10,11- phylums platyhelminthes and nematoda flatworms and roundworms
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Ch. 10,11- Phylums Platyhelminthes and Nematoda
Flatworms and Roundworms
Phylum Platyhelminthes
• Largest group of acoelomate (no body cavity) worms
• Flatworms with middle tissue layer- mesodermmesoderm• 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
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
-- 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
Planarian
Phylum Platyhelminthes • Many parasitic
– Endoparasite- internal– Ectoparasite- external
• Class Cestoidea• Subclass Eucestoda- Parasitic
flatworms (tapeworms)– Suckers and hooks attach to walls of
intestines and food absorbed from host’s intestines directly through the tapeworm’s skin
– String of rectangular body sections (proglottidsproglottids)
• Each proglottid is a reproductive unit• Added continually through life• May grow up to 12 m (40 ft.) long
• 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
Phylum Platyhelmithes
Phylum Platyhelminthes• Largest flatworm class,
Trematoda– Parasitic worms called flukesflukes– Endoparasites Endoparasites or ectoparasitesectoparasites
• Subclass Aspidogastrea (Aspidobothrea)- Subclass Aspidogastrea (Aspidobothrea)- Endoparasite of mollusksEndoparasite of mollusks
• Subclass Digenea- Endoparasites of Subclass Digenea- Endoparasites of vertebratesvertebrates
– Tegument- 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
• 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– Class Monogenea- Monogenetic
flukes• One life cycle in one host• Mostly ectoparasites on vertebrates
Phylum Platyhelminthes
Liver fluke
•
Phylum Nematoda
• Roundworms- have a pseudocoelempseudocoelem (body cavity between endoderm & mesoderm)– Fluid movement serves as
circulatory and gas exchange system
– Fluid also distributes nutrients to cells from digestive system
• Long, cylindrical bodies• Majority microscopic and
free-living• One-way digestive system• Thick, flexible epidermisepidermis
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 trichinosistrichinosis (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 • Hookworms attach to
the inside of the digestive tract
• Often found in pets
• 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