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Unsegmented worms
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1. Phylum Platyhelminthes
Otherwise known as FLATWORMS Characteristics: - bilateral symmetry - cephalization (development of nervous tissue at “head” end)
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Free Living Flatworm (planaria)
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Physiological Characteristics
Feeding & Digestion Some are carnivores (suck food in at pharynx, branches into gastrovascular cavity Enzymes in cavity break down food which diffuses into body cells Some are parasites (feed on blood/tissue or host’s digested food) Circulation & Respiration Diffusion of O2 & CO2 across epidermal cells Flame cells help get rid of excess water Flame cells empty into tiny pores
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More… Nervous System Free living worms have a “head” region & cephalization & primitive brain Long nerve cords (2) run down sides of body Ocelli sense light & dark Parasitic flatworms DO NOT have nervous tissue Locomotion (free living) Cilia in epidermal cells Muscle cells allow for twisting & turning Reproduction Most are hermaphrodites (both male & female) Sexual: between 2 worms (egg fertilized by sperm) Asexual: binary fission
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Class Turbellaria Example: Planarians, “cross eyed” freshwater worms
Features: Flatworms; live in a variety of environments (land, fresh water, oceans)
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Class Trematoda Example: Flukes (ex. Blood flukes)
Features: Parasitic (internal or external); complex life cycle often involving several hosts Reproduce sexually or asexually Many are hermaphrodites
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Class Cestoda Example: Tapeworm
Features: Parasitic (most live in intestines of host) Scolex (head) contains suckers to embed in intestinal wall Absorbs nutrients from host
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Fun with Flukes!
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2. Phylum Nematoda Otherwise known as ROUNDWORMS
Simple digestive system (mouth intestines anus) Range in size Most are free living; some parasitic
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Physiological Characteristics
Feeding & Digestion Long tube (mouth anus) Many are carnivores, although some feed on decaying plant material Circulation & Respiration Diffusion; transfer of nutrients & gases internally also through diffusion
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More… Nervous System GANGLIA in “head” region
Long nerves run down length of body allow for movement Examples: hookworms, Ascaris (parasitic intestinal worm)
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