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Among the most numerous of animals (more than a million in a bucket of pond water or garden soil) Slender, unsegmented, with tapering ends Most microscopic, but can be more than 1 meter in length Free-living or parasitic Respiration and Circulation occur through simple diffusion Some cephalization - simple brain in head region Many types have separate males and females (only some are hermaphroditic) Fertilization is internal Live in soil, salt flats, aquatic sediment, and water (from polar regions to tropics) Eat microscopic animals, fungi, algae, bacteria, or detritus (dead leaves) Have a tube-like digestive system with two ends: mouth and anus Source Although most roundworms are free-living, the parasitic roundworms are most well known Examples include Trichinosis-causing roundworms, filial worms, ascarid worms, and hookworms Trichinosis causes severe pain as the worms burrow through the tissues Filial worms spread from host to host by biting insects (mosquitoes) Live in blood and lymph tissues of the host which may lead to elephantiasis (lymph vessels are blocked by too many worms) Ascaris lumbricoides is found in more than 1 billion people worldwide, leading to malnutrition Live in the intestine and/or bloodstream of the host Ascarid worms may reach up to 50 cm in length! (Link to convert to inches = http://www.worldwide metric.com/metcal.htm) 25% of the world’s population is affected Found in the soil, they use their sharp hooks and teeth to burrow into the skin and enter the bloodstream They then travel to the lungs and then to the small intestine where they stay as adults. Ancylostoma duodenale Necator americanus http://www.dpd.cdc.gov/DPDx/HTML/Para _Health.htm Please choose from one of the categories below or from the alphabetical listing at left.