The Roundworms

 Triploblastic Pseudocoelomate  Three tissue layers  False Body Cavity No Mesentery (thin connective tissue) to support the organs) Fluid filled and acts as a hydrostatic skeleton, provides for circulation, aids in digestion

 Complete Digestive System (mouth to anus)  Most are microscopic  Bilateral Symmetry  Unsegmented  Most dioecious

 Epidermis is covered by an external cuticle that is often molted for growth

 Glandular in aquatic species  Tubular in parasitic species

 Cerebral ganglion- around the pharynx  Two longitudinal nerve cords

 Free living roundworms can be carnivorous or herbivorous, usually soil dwellers feeding on small or microscopic organisms  Parasitic roundworms feed off of their host tissues and fluids

 No circulatory system  Pseudocoel fluid serves to circulate some nutrients and wastes  No respiratory system  Gas exchange across skin-diffusion

 Dioecious  Often dimorphic  Males and females are different sizes  Method of reproduction varies by species

 Ascaris lumbricoides  Giant intestinal roundworm  Enterobious vermicularis  Human pinworm  Necator americanus  New world hookworm  Trichinella spiralis  Porkworm  Wuchereria sp.  Filarial worms (elephantiasis)  Dirofilaria immitis  Dog heartworm

 Rotifers-usually water dwellers  Gordian (horsehair) worms- live in running or standing water