Animal Bio: Flatworms

Phylum

Nemertea and Platyhelminthes

Flatworms (Platyhelminthes)

marine, freshwater, moist terrestrial, parasitic environments (prevents drying out)

bilateral symmetry and cephalization

acoelomate (no body cavity) and dorsoventrally flattened

organ grade or organization

triploblastic lophotrochozoan protostomes (crown of cilia around mouth to help feed)

no respiratory, circulatory or skeletal systems (oxygen diffuses)

Free-living flatworm muscles and epidermis

ciliated epidermis (helps movement) with rhabdites (rodlike and produce mucus to protect against desiccation and trap food)

parasitic flatworms

tegument (epidermis connected to help adapt to parasitic lifecycle) secretes, and fewer spaces for worm to be attacked in a host

body filled with parenchyma (gel-like matrix)

muscle fibres run through parenchyma, arranged in layers under epidermis

gut

incomplete or absent altogether

digestion

in intestine is intracellular and extracellular

undigested food regurgitated by pharynx

pharynx in free-living flatworms

projects from mouth

host tissues in flukes is…

ingested by oral sucker

tapeworm absorption

soluble molecules absorbed across tegument

nervous system

brain, longitudinal nerve cords, transverse nerves (like linear nerve net) forming later of neural networks

neurons: sensory, or motor (receive info and perform action)

sense organs (ocelli)

eyespots

sense organs (chemoreceptors)

chemicals that tell them to move away, move forward, what to do etc.

sense organs (tactile)

to tell them how to react to what they are touching

sense organs (cerebral ganglion)

first thing encountering what they move into and receives info

reproduction

monoecious (sperm and eggs) internal fertilization

eggs in cocoons attached to plants in turbellarians (free-living flatworms)

eggs produced ciliated larvae in marine and parasitic forms

regeneration

turbellarians divide asexually as well

penis fencing

fight each other to pierce the epidermis and inseminate (and avoid being inseminated themselves)

Class Trematoda (Flukes)

look like a leaf, have organs for adhesion (suckers, hooks)

sense organs poorly developed

Parasitism (flukes)

smaller participant (parasite) uses larger one (host) as habitat and source of nutrients; host is harmed, often killed

Endoparasitic (flukes)

live outside host usually in digestive system

definitive host often vertebrate

intermediate host is mollusc (ex: snail)

that will undergo asexual reproduction

Class Turbellaria (free-living flatworms)

marine, freshwater, moist and terrestrial habitats

move via cilia or production of slime track (Infolds move)

Schistosoma (blood flukes)

infect ~252 million people

dioecious (either egg or sperm)

eggs pass in faeces after sexual reproduction

start in liver of host and produce eggs in intestines

ciliated miracidia find and penetrate snail (asexual division)

cercariae released from snail penetrate skin of human and go back into liver

adult worms mate

eggs travel to intestine (cause ulcers and abscesses)

Class Cestoda (tapeworms)

endoparasitic

monoecious (sperm and eggs)

suckers, hooks

no digestive system

microtriches on tegument absorb food molecules

strobila (body) tapeworms

consists of proglottids (sac of eggs) produced behindd scolex and makes them get bigger and bigger

scolex (head) tapeworms

like head w barbs that help attach to host)

Taenia Saginata (beef tapeworm)

cattle are intermediate host (asexual reproduction), human is definitive host (sexual reproduction)

eat meat with cyst if not cooked right (turn into adult and feed off you)

proglottid passes out of human

eggs eaten by cattle

larva encysts in muscle

cyst opens, worm emerges and grow into adult

Phylum Nemertea (ribbon worms)

marine worms

ciliated epidermis

complete digestive system

simple circulatory system

dioecious (sperm or egg)

rhynchocoel (ribbon worms)

houses long, proboscis (not true body cavity but sits inside worm and everts out to help them catch prey)