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

NematodesCharacteristics

Slender, unsegmented w/ tapered endsRange from microscopic to 1 meter longMost are free-living, some are parasiticDevelop from three germ layers

Have a body cavity b/w endoderm and mesoderm

PseudocoelomateHave a digestive tract with two openings

Form and functionFeeding

Free living worms are predators with grasping mouth partsSoil dwelling and aquatic forms eat algae, fungi or decaying organic matter

Respiration, Circulation and ExcretionThese processes take place by diffusion

ResponseSimple nervous system with several gangliaNumerous sense organs

MovementNematodes have muscles that extend the length of the bodyUse the pseudocoelom and a hydrostatic skeleton

ReproductionSeparate male and female organismsReproduce sexually using internal fertilizationParasitic 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 insectsCause elephantitis extreme swelling due to buildup of fluid

Ascarid wormsAscaris lumbricoides

Mature in intestine and release eggs in fecesFeces can contaminate food or water continuing cycleCauses malnutrition

Hookworms soil dwellingLay eggs in soilPierce feet to burrow into skin and enter blood streamConsume 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