Transcript Platyhelminthes - The Bronx High School of Science

“Radiata”
Metazoa
Ancestral colonial
flagellate
Deuterostomia
Eumetazoa
Protostomia
Bilateria
Phylum: Platyhelminthes
Nematoda
Nemertea
Rotifera
Arthropoda
Annelida
Mollusca
Platyhelminthes
Chordata
Echinodermata
Brachiopoda
Ectoprocta
Phoronida
Ctenophora
Cnidaria
Porifera
Kingdom: Animalia
Phylum: Platyhelminthes
Class:
Trematoda
parasitic flukes
Class: Cestoda
parasitic tapeworms
Class:
Turbellaria
free-living planaria
Phylum: Platyhelminthes
•flatworms
•most primitive animal that has/is...
•bilateral symmetry
•dorsal/ventral; anterior/posterior; left/right
•triploblastic
•endoderm- digestive system
•ectoderm- outer covering, nervous system
•mesoderm- muscle, excretory, reproductive
systems
•tissue level of organization
•true organs
•believed to be first animal that could hunt for food;
aided by bilateral symmetry and paired sense organs at
the head
•acoelemate
•no body cavity (i.e. “solid body”)
•only internal cavity is the gut
Phylum: Platyhelminthes
•acoelemate
•no body cavity (i.e. “solid body”)
•only internal cavity is the gut
Phylum: Platyhelminthes
•no organized circulatory or respiratory systems
•thin,flat bodies allow diffusion of nutrients and gases
•centralized nervous system (cephalization)
•brain and sensory organs at head
•2 nerve cords run length of body
•digestive system
•free-living planaria has branched one; single opening
•parasitic tapeworm has none
•reproductive system
•sexual- hermaphrodites
•both testes and ovaries, uterus in mesoderm
layer
•cross- or self-fertilization
•asexual
•binary fission
•fragmentation and regeneration
Phylum: Platyhelminthes
Class: Turbellaria
•free-living flatworms
•may have ciliate as ancestor
•size range from <1-60 cm
•locomotion
•layers of muscles
•cilia
•some have glands that secrete mucus
to glide along
•most are carnivorous, scavengers
•habitat
•most marine or freshwater
•some on humid land
Phylum: Platyhelminthes
Class: Turbellaria
•well-defined nervous system w/ sense organs
•ganglia concentrated as simple brain at head
•sensory cells (statocysts sense gravity, light
sensory cells at eyespots, chemosensory cells)
•2 nerve cords run length of body
•simple excretory system- protonephridia
•consists of flame cells (specialized ciliated cells)
•move fluid through branched ducts to outside via
excretory pores
•maintains osmotic balance
Phylum: Platyhelminthes
Class: Turbellaria
•digestive system (2-way system)
•branched w/ single opening
serving as mouth/anus
•mouth, muscular pharynx,
intestine
•digestion is extracellular and
intracellular
•digestive enzymes
secreted into digestive
cavity
•small food particles enter
ameboid cells by
phagocytosis and digested
in food vacuoles
Phylum: Platyhelminthes
Class: Turbellaria
Reproduction
•asexual by binary fission
•sexual- hermaphrodites
•cross-fertilization
•some mate by “penis-fencing”
•sperm injected in body wall
•fertilization and early
development inside “mother”
•juveniles that resemble adult
released
Phylum: Platyhelminthes
Class: Turbellaria
organ systems
•digestive
•nervous
•reproductive
•excretory
Phylum: Platyhelminthes
Class: Turbellaria
Convoluta roscoffensis
•mutualistic relationship
•ingests photosynthetic
flagellates
•flagellates lose flagella and cell
wall and take up residence in
worm gut
•as adult, worm no longer feeds
and survives off of flagellates
•later in life, worm digests
flagellates and all die
Phylum: Platyhelminthes
Class: Turbellaria
Genus: Bdelloura
•commensalism with horseshoe crab
•attaches to gills or appendages of horseshoe crab
•worm gets transportation, shelter, food scraps
Phylum: Platyhelminthes
Classes: Cestoda, Trematoda ”The parasitic
flatworms”
•most have 2 or more hosts during life cycle
•intermediate host- juvenile stage
•definitive host- adult stage
•much of structure devoted to reproduction
•produce lots of offspring to make it to the next host
•do not survive long outside of host
•contain unusual epidermis called tegument
•protects against detection/digestion by host
•some have microvilli to aid absorption of host
nutrients
•some syncytial (cells have continuous cytoplasm)
to aid in distribution of nutrients
•some secrete their own digestive/protective
enzymes
Phylum: Platyhelminthes
Class: Trematoda
•parasitic flukes
•live in intestine, liver, lungs, bladder and blood
vessels
•involve at least 2 hosts
•reproduction
•asexual in early life stages
•sexual in adult stages producing large numbers
of eggs stored in uterus
Phylum: Platyhelminthes
Class: Trematoda
Genus: Schistosoma
•causes human disease schistosomiasis
•major world health problem
•common in Africa, Asia and South America
•chronic disease
•acute symptoms: fever, rash, body pains, cough,
dysentery
•long term: can cause organ damage; rare lesions
in central nervous system
•hosts•intermediate is aquatic snail
•definitive is human (or other vertebrates)
cercaria
adult
Phylum: Platyhelminthes
Class:
Trematoda
Genus: Schistosoma
Life cycle stages:
•eggs hatch into miracidium (larval stage, swimming
ciliate, can only live 24 hrs outside of host)
•miracidium enters snail and becomes sporocyst (loses
cilia)
•sporocyst reproduces asexually to produce more
sporocyst or redia
•redia becomes cercaria (swimming stage that
resembles adult form)
•cercaria leaves first host and enters vertebrate host
(release digestive enzymes to help bore through skin)
•once in host, cercaria migrates through blood to large
intestine and becomes adult to produce more eggs
Phylum: Platyhelminthes
Class: Trematoda
Chinese liver fluke
Hosts:
snail>fish>mammal (human)
In definitive host...
•cysts digested in intestine
releasing fluke
•fluke travels up bile duct to
liver
•attaches with suckers and
feeds on blood
•causes anemia and liver
disease
•may block bile duct
Phylum: Platyhelminthes
Class: Trematoda
Liver flukes
Phylum: Platyhelminthes
Class: Cestoda
•tapeworms
•parasitic
•as long as 100 feet
•most have at least 2 hosts
•no digestive system; nutrients absorbed from host
•scolex = specialized head that has sucker discs and
hooks for anchoring to host
Phylum: Platyhelminthes
Class: Cestoda
•long flat body made of many
units called proglottids
•proglottid = complete
reproductive unit with male and
female gonads
•youngest proglottid behind
head
•older proglottids w/ eggs shed
in feces of definitive host
•reproductive output high
•many proglottids per tapeworm
•many eggs per proglottid
Phylum: Platyhelminthes
Class: Cestoda
Beef
tapeworm
life cycle
Phylum: Platyhelminthes
Class: Cestoda
•Beef tapeworm life cycle (Taenia saginata)
•cattle ingest human feces with eggs and egg
covering digested off to reveal larva with scolex
that bores through intestinal wall to blood vessel
to muscle
•larva grows in muscle to form a cyst called
“bladder”
•human eats undercooked meat with “bladder”
•cyst digested open releasing tapeworm
•scolex attaches to intestinal wall and tapeworm
grows, makes new eggs
Phylum: Platyhelminthes
Class: Cestoda
•Pork tapeworm
•similar to beef tapeworm but pig is intermediate host
•can also develop bladders in human host
•can grow in eye or brain (interfere with vision or cause
seizures
•Broad fish tapeworm (Diphyllobothrium latum)
•eggs reach freshwater to produce free swimming larva
•eaten by copepods (small crustaceans)
•copepods then eaten by fish
•humans can get by eating raw or undercooked fish
•absorb vitamin B-12 and can cause megaloblastic
anemia
Platyhelminthes- The Table
•Symmetry- bilateral
•Segmentation- N/A
•Mesoderm present- yes, triploblastic
•Determinant cleavage
•Type of body cavity- acoelomate, “solid body”, lack
body cavity other than digestive cavity
•Ciliated larva- trocophore-like in some (freeswimming, ciliated)
•Protostome- N/A; mouth=anus
•Nervous system- cerebral ganglia form simple
brain, 2 nerve cords, specialized sensory cells
•Respiratory system- none, flat and thin for
respiration by diffusion across cell membranes
Platyhelminthes- The Table
•Digestive system- Turbellaria has highly
branched one but still 2-way (mouth=anus);
Trematoda has some digestive tract; Cestoda
has no digestive tract, absorbs food through
external surface
•Excretory system- Excrete using ciliated
flame cells that push wastes through
excretory ducts and out excretory pores
•Reproductive system- contain testes and
uterus; planaria are hermaphrodites; can
reproduce by binary fission and
fragmentation/regeneration
Platyhelminthes- The Table
•Circulatory system- none; relies on flat thin
body for diffusion across cell membranes
•Members- Most are parasitic including
Cestoda (tapeworms) and Trematoda
(flukes). Turbellaria are free-moving and not
parasitic.