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8.2 Roundworms and Segmented Worms • The Roundworm is the most common type of worm in the sea. •In fact they are one of the most popular species in the world. •Their scientific name is nematode. •The nematode species are extremely difficult to tell apart from each other. •http://www.youtube.com/watch?v=tp-O3LME3OU Environment of Roundworms • Small round worms live in sand and mud • Most worms are found in the moist substrate of the intertidal zone Roundworm movement • To move the roundworm whips the back half of its body around • They are able to move through tiny spaces between sand grains • Some worms can actually swim thirough the water • The motor skills are located in the top of the head called the, ganglia. Roundworm appearance • Roundworms are very very small • Different sexes • They are characterized by a cylindrical body shape • Fertilization is internal • Development is external. • Males and females differ in size and shape Roundworm body • • • • Feed on organic debris Have one way digestive track No circulatory or respiratory system Respiratory gases and cellular wastes pass through its skin Segmented worms • The earth is the most common worm on the planet • The body of a segmented worm is divided into parts • They are called segmented worms or annelids The Sandworm • Live in muddy sands in the intertidal zones and subtidal zones • They prey on tiny invertebrates and they search for organic debris • Some live inside tubes • They have hair like bristles called setae • They have a nervous system to coordinate the movements of the body Sandworm continued • They breathe through their skin like earthworms • Carbon dioxide diffuses from the inside of the body to the outer environment • Nutrients and respiratory gases are transported through the body via the closed circulatory system • They also have a well-developed excretory system Blood worm • • • • The bloodworm is a polychaete Has an open circulatory system They also borrow in the sand Small and have a thread like appearance The leech • This segmented worm has no bristles • Also called Hirudinea • Some are free-living and some attach to hosts • They have sharp teeth located at the front of its body • It secretes a chemical called hirudin to prevent the host’s blood from clotting THE END/Citations Thomas F. Greene. Marine Science. Brooklyn, New York: Amsco School Publications, 2004. Wlanier. “A Marine Nematode Roundworm.” August 25, 2006. <http://www.youtube.com/watch?v=tpO3LME3OU>