Roundworms (Phylum Nematoda)

Features Bilateral symmetry and 3 cell layers Plus a “pseudocoelom” (fluid filled space betwen the mesoderm and internal organs) Have a complete (one-way) digestive tract (mouth – anus) Mostly free living, but some are parasitic Can be anywhere from very tiny microscopic to 1 m in length!

Form and function Digestion:  Called an “intestine”, not a gastrovascular cavity (remember, this one is one way) Respiration and circulation:  No organised system. O 2 and CO 2 diffuse through the skin Excretory system:  2 excretory canals with pores (openings) near anterior end

online/library/onlinebio/BioBookDiversity_7.html

Nervous system:  Head, dorsal and ventral nerves Musculoskeletal system:  Longitudinal muscles only Reproductive:  Sexual reproduction only  Seperate sexes and females are usually larger

Ecology of unsegmented worms Free living flatworms and roundworms are usually small and don't affect humans much We pay more attention to the parasitic ones, which cause many horrific diseases

Roundworm Parasites Ascaris Video!Video! Hookworm Filaria worm (elephantitis) Trichinella (trichinosis) undercooked pork Eye worms

Ascaris lumbricoides Life cycle (pg ) lives in the intestine of the human after consuming undercooked meat/pok

Hookworm infection Baby worms burrow through soles of feet! Larva cause massive damage when they migrate from lungs to the intestine

Filaria worm Transferred by mosquito Block lymph capillaries and causes elephantitis

Guinea worm Roll it with a pin to pull it out of the flesh