Unsegmented Worms

Flatworms

Flatworms Belong to the phylum platyhelminthes. (Plat = flat) There are three classes: Turbellaria Trematoda Cestoda

Characteristics of Flatworms They are acoelomates (they don’t have body cavities) They have bilateral symmetry Show cephalization Respiration, excretion, and circulation through skin (diffusion) Single opening to digestive tract (pharynx)

Characteristics of Flatworms Soft, flattened bodies Have tissues and organ systems Have 3 germ layers (endoderm, mesoderm, and ectoderm) Can be free-living or parasitic Around 20,000 species

Characteristics of Flatworms Sexual reproduction: mutual copulation Asexual reproduction: fragmentation and regeneration Have simple “brains” (nerve clusters) with nerve cords that run down body (free-living) Movement by small muscles and cilia

Classification Class Turbellaria Class Trematoda (flukes) Dugesia (planarian) Class Trematoda (flukes) Schistosoma Class Cestoda (tapeworms) 7

Class Turbellaria Spade-shaped head and two eyespots (light detection) Eat protozoans (scavengers) Flame cells (protonephridia) remove waste Are hermaphrodites (have male and female reproductive parts) Can reproduce by regeneration Are free-living

Class Trematoda Are parasitic flukes Have suckers on both ends of the body Most live in internal organs of host Can live inside or outside of host (endo- or ectoparasites)

Class Trematoda Nervous and excretory systems like turbellarians Hermaphrodites Have complex life cycles usually involving two hosts

Class Trematoda (Flukes) Schistosomiasis: disease caused by parasitic blood flukes (Schistosoma); infects people in Asia, Africa, and South America causing intestinal bleeding and tissue decay that can result in death

Fluke Life-Cycles The long and complex life-cycle of the fluke can be made easier to understand through the use of a nonsense mnemonic : Every - Egg Man - Miracidium (free-living in water) Sees - Sporocyst (in snail) Red - Redia (in snail) Colored - Cercaria (free-living in water/snail) Money - Metacercaria (in 2nd intermediate host) A - Adult

Class Cestoda Parasitic Tapeworms Long, ribbon-like bodies Absorbs nutrients from host Hermaphrodites Grow by adding proglottids (body sections): each contains male and female reproductive organs

Tapeworm Anatomy Tegument: tough, non-cellular body covering of parasitic worms Scolex: anterior end, contains hooks & suckers for attachment to intestine of host

Roundworms Roundworms

Roundworms Belong to phylum Nematoda Pseudocoelomates (fluid filled body cavity) Slender bodies that taper on both ends Have mouth and anus (0ne-way) Can be free-living or parasitic

Roundworms Microscopic to a meter in length Predators, detritivores (eat dead material) Use diffusion for respiration, circulation, and excretion Nervous system like flatworms

Roundworms Move using muscles and hydrostatic skeleton Reproduction is sexual w/separate species 25,000 species named; actual # ~500,000

Roundworms Marine, freshwater, and soil dwellers; every climate

Trichinosis- a disease from eating infected pork

Roundworms & Disease Trichinosis (Trichinella spiralis) - cysts within the muscles are consumed (undercooked food) -- worm grows in intestine -- forms cysts in the muscles of the new host -- symptom: terrible pain in muscles

Cysts in Contaminated Pork

Filarial Worms - found in Tropical regions of Asia; also in blood and lymph vessels of birds and mammals (heartworms) -- usually transmitted by mosquitoes -- causes elephantiasis

Ascarid Worms (common roundworm) Ascaris lumbricoides - lives in intestine - eggs are passed out in the feces Most roundworms infect dogs, but occasionally they find their way into human hosts

Hookworms Ancylostoma duodenale: - burrow into the skin from soil - mature in the intestines --hooks used to attach and suck blood

Pinworms live in human intestines (Enterobius vermicularis)

Research on C. elegans (free living roundworm) first organism to have DNA completely sequenced It is a very simple, free living roundworm

Phylum Rotifera Known as rotifers or wheel animals Transparent, free-swimming microscopic animal Freshwater & marine Have a ring of cilia around mouth that rotates like a wheel to bring in food Feed on unicellular algae, bacteria, & protozoa

Rotifers Have a muscular organ called the mastax behind the pharynx to chop food Nervous system composed of anterior ganglia & 2 long nerve cords Show cephalization (head end) Have 2 anterior, light-sensitive eyespots

Rotifer Anatomy