Unsegmented WormsUnsegmented 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 through skin

• Single opening to digestive tract (pharynx)

Class Turbellaria

• Spade-shaped head and two eyespots

• Eat protozoans for scavenge

• Flame cells 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

• Can live inside or outside of host

Class Trematoda

• Nervous and excretory systems like turbellarians

• Hermaphrodites

• Have complex life cycles

Fluke Life-CyclesThe long and complex life-cycle of the fluke can be made easier to understand through the use of a nonsense mnemonic :Every - EggMirror - Miracidium (free-living in water)Spotted - Sporocyst (in snail)Red - Redia (in snail)Certainly - Cercaria (free-living in water/snail)Met - Metacercaria (in 2nd intermediate host)Approval - Adult

Class Cestoda

• Parasitic

• Tapeworms

• Long, ribbon-like bodies

• Absorbs nutrients from host

• Hermaphrodites

Tapeworm Anatomy

RoundwormsRoundworms

Roundworms• Belong to phylum Nematoda

• Pseudocoelomates (fluid filled body cavity)

• Slender bodies that taper on both ends

• Have mouth and anus

• Can be free-living or parasitic

Pinworms live in human intestines

Trichinosis- a disease from eating infected pork

Cysts in Contaminated Pork

Rotifers• 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