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Explore the diverse life forms of flatworms and roundworms, from free-living planarians to parasitic tapeworms and flukes. Learn about their feeding habits, nervous systems, and unique life cycles, with stunning marine flatworms and common roundworm infections detailed.
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Chapter 25 Worms & Mollusks
Flatworms • Phylum Platyhelminthes • Acoelomates • Thin, solid bodies • Bilateral symmetry • Found in marine, freshwater, and moist habitats on land • Examples: tapeworms, flukes, and planarians
Feeding and Digestion in Planarians • Feed on dead or slow moving organisms • It extends the pharynx out of its mouth • Enzymes digest the food outside of the body • Food is sucked into pharynx
Planarians • Head – senses and responds to the environment • Eyespots – sensitive to light • Sensory pits – used to detect food, chemicals, and movements in the environment • Pharynx – muscular tube that extends outside the body to digest food • Cilia – underneath, help with moving the planarian • Flame cells – helps to remove water from the planarian’s body
Head Eyespot Nerve chord Digestive Cavity
Nervous Control in Planarians • Some have a nerve net and others have a simple central nervous system • Ganglia receive messages from the eyespots and sensory pits and then communicates with the rest of the body through nerve cords
Reproduction in Planarians • Asexually, they regenerate body parts by mitosis • Most are hermaphrodites • Sexually- two flatworms exchange sperm to fertilize eggs internally • Zygotes are released in capsules into water
Diversity of Flatworms • Planarians are free-living • Tapeworms and flukes are parasites which live in many vertebrates (dogs, cats, cows, humans, etc.) Tapeworm Fluke
Feeding and Digestion in Parasitic Flatworms • Parasites live on or in another organism and depends on it for food • Have mouthparts with hooks to attach to host • They do not have a complex nervous system, muscular tissue, or digestive organs because they are surrounded by nutrients
Tapeworm bodies have sections • The body is made of a head and repeating sections called proglottids • Scolex – head • Proglottid – contains muscles, nerves, flame cells, and reproductive organs
The Life Cycle of a Fluke • Adults live in blood vessels • Fluke eggs pass out of body in waste product • Eggs hatch into free-swimming larvae and enter the snail host • Larvae develop and reproduce in the snail and then leave the snail • When humans walk in water, the flukes bore through the skin and enter the bloodstream and into the intestines
Chapter 25.2 Roundworms and Rotifers
Roundworms • Phylum Nematoda • Live in soil, animals, freshwater, and saltwater • Most are free-living, but some are parasitic • Tapered at both ends • Thick outer coverings • Have longitudinal muscles to make the worm move back and forth • Pseudocoelomate • Two openings: a mouth and anus
Nematode- roundworm Two Roundworms Reproducing
Roundworm Diversity • Ascarisinfect mostly children who put soil into their mouths or eat veggies that are not cleaned • Intestines to bloodstream to lungs • Hookworms infect humans walking barefoot in warm climates • Cause weakness due to blood loss
Ascaris Ascaris (Intestinal Roundworm)- These nematodes are found exclusively in humans and are present mostly in unsanitary areas without modern plumbing. Around one in six people worldwide are infected by Ascaris (Raven et al. 746). A study conducted in Cameroon focused on school children and found that 65.5 % were infected with Ascaris parasitic roundworms. Ascaris eggs are spread through feces, and, when ingested, hatch and bore through the intestinal wall. They move to the heart, the lungs, and finally out the breathing passages where they are swallowed, thus perpetuating the cycle. Females lay hundreds of thousands of eggs each day and can reach nearly 30 centimeters in length (Raven et al. 746).
