FLATWORMS Belong to the Kingdom Animalia Phylum Platyhelminthes

Characteristics Three germ layers (endoderm, ectoderm, mesoderm) Bilateral symmetry Cephalization (has a head) COELOM = fluid filled body cavity Acoelomates = without coelom

FORM AND FUNCTION FEEDING Free-living - carnivores or scavengers; they have a digestive cavity, mouth and pharynx Parasites – feed on blood, tissues or pieces of cells from within a HOST Most do not have a complete digestive system because they absorb material directly from host

Respiration, Circulation, and Excretion Thin bodies allow for materials to diffuse (respiration, excretion, etc) Flame Cell – specialized cells that remove excess water/waste

Response Ganglia – group of nerve cells that control the body (like a brain) Eyespot – group of cells that can detect light (like an eye)

Movement Flatworms move in 2 ways Cilia helps them glide through the water Muscle cells help them twist and turn

Reproduction Sexual Reproduction – most flatworms are hermaphrodites (have both male and female sex organs) Asexual Reproduction by transverse fission – flatworms can split in two and regenerate

Groups of Flatworms CLASS TURBELLARIA - free living flatworms - live in fresh or marine water - ex. Planarian

Dugesia lives in freshwater, mostly a scavenger but can also feed on protists

Planarians are hermaphrodites They can also regenerate body parts and will sometimes split in half to reproduce (TRANSVERSE FISSION)

ANATOMY OF A PLANARIAN

Brain (ganglia) - planarian can process information about their environment Pharynx - used for suckling food in (the mouth is at the end of the pharynx) Eyespot - simple eye, can detect light Flame cells - located along the lateral edges, used for excretion Intestine - digestion (does not have an anus)

Class Trematoda = parasitic flatworms a.k.a “flukes” live in mouth, skin, or gills of host Primary host = the host in which a parasite reproduces sexually Intermediate host = the host in which asexual reproduction occurs

Schistosoma mansoni - multiple host: Primary host = human Intermediate host = snail Causes Schistosomiasis -in humans; decays lungs liver, spleen, or intestines, occurs in tropical areas with poor sanitation/sewage.

Class Cestoda =tapeworms Long, flat, parasitic Live in intestines

Scolex = a structure that contains suckers and/or hooks Proglottids = body segments of the tapeworm

Each mature proglottid is hermaphroditic Testes produce sperm -> fertilize the eggs to produce a zygote Zygotes (fertilized eggs) are passed out through the feces.

Sometimes, a dormant, protective cyst is formed in the intermediate host muscles ****This is why you should never eat incompletely cooked meat.