NEMATODAThe Roundworms

BASIC CHARACTERISTICS Triploblastic

PseudocoelomateThree tissue

layersFalse 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

BASIC CHARACTERISTICS (CONTINUED) Complete

Digestive System (mouth to anus)

Most are microscopic

Bilateral Symmetry

Unsegmented Most dioecious

INTEGUMENTARY SYSTEM Epidermis is covered by an

external cuticle that is often molted for growth

EXCRETORY SYSTEM Glandular in

aquatic species

Tubular in parasitic species

NERVOUS SYSTEM Cerebral

ganglion-around the pharynx

Two longitudinal nerve cords

FEEDING AND DIGESTION 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

CIRCULATION AND RESPIRATION No circulatory system

Pseudocoel fluid serves to circulate some nutrients and wastes

No respiratory systemGas exchange across skin-diffusion

REPRODUCTIVE SYSTEM Dioecious Often dimorphic

Males and females are different sizes

Method of reproduction varies by species

PARASITIC NEMATODES Ascaris

lumbricoidesGiant intestinal

roundworm Enterobious

vermicularisHuman pinworm

Necator americanusNew world

hookworm

Trichinella spiralisPorkworm

Wuchereria sp.Filarial worms

(elephantiasis)

Dirofilaria immitisDog heartworm

OTHER PSEUDOCOELOMATES (ASCHELMINTHS) Rotifers-usually

water dwellers

Gordian (horsehair) worms-live in running or standing water