Phylum Nematoda (Chapter 27.2) Please set up your notebook for Cornell Notes

Nematodes Characteristics Slender, unsegmented w/ tapered ends Range from microscopic to 1 meter long Most are free-living, some are parasitic Develop from three germ layers Have a body cavity b/w endoderm and mesoderm Pseudocoelomate Have a digestive tract with two openings

Form and function Feeding Free living worms are predators with grasping mouth parts Soil dwelling and aquatic forms eat algae, fungi or decaying organic matter Respiration, Circulation and Excretion These processes take place by diffusion

Response Simple nervous system with several ganglia Numerous sense organs Movement Nematodes have muscles that extend the length of the body Use the pseudocoelom and a hydrostatic skeleton

Reproduction Separate male and female organisms Reproduce sexually using internal fertilization Parasitic roundworms have life cycles that involve two or three host or multiple organs in one host

Roundworms and Human Disease Trichinosis  caused by Trichinella Mate in intestines of host, larva are released into the blood stream to take up residence in various organs, become inactive cysts in muscles cells Extremely painful Common hosts are pigs and rats Human contract by eating undercooked, infected pork

Filarial worms  threadlike worms that live in blood and lymph vessels of birds and mammals Transmitted by biting insects Cause elephantitis  extreme swelling due to buildup of fluid

Ascarid worms Ascaris lumbricoides Mature in intestine and release eggs in feces Feces can contaminate food or water continuing cycle Causes malnutrition

Hookworms  soil dwelling Lay eggs in soil Pierce feet to burrow into skin and enter blood stream Consume blood causing weakness and poor growth

Pinworms  most common parasitic infection in US Adults live in large intestine Migrate to anal region to lay eggs Results in intense itching that spreads eggs to clothes and bedding