segmented worm

bumpy body; segmented body plan; three germ layers

round worms

nematodes; mostly tiny; everywhere!

flat worms

mostly parasites; include tapeworms, flukes, planarians, and marine flatworms

structure of worms

bilateral symmetry; 2-3 germ layers; parasitical and free-living; breathe thru epidermis; aquatic have gills

extracellular digestion

the breakdown of substances that occurs in spaces outside of cells, such as within the stomach or intestine

ganglion

a bundle of nerve cells

closed circulatory system

a system of fluid circulation within organisms in which the fluid, typically blood, remains within vessels