Flatworms and related phyla Flashcards
benefits of bilateral symmetry
- forward, directed movement
- cephalization (formation of a head region)
bilateria are _____ organisms
triploblastic which means they have 3 germs layers (gut, endoderm, mesoderm, ectoderm)
advantages of more germ layers
- give rise to specific tissues and organs; tissue level of organization
- more complex
- diverse
ex of ectoderm, mesoderm, endoderm in mammals
- ectoderm; skin, hair, nails, mouth lining, tooth enamel
- mesoderm; kidneys, gonads, circulatory system, muscles, notochords, body cavity
- endoderm; lining of GI tract, respiratory tubes, liver, pancreas
3 clades of bilateria that we look at
- lophotrochozoa
- ecdysozoa
- deuterostomia
what 4 lophotrochozoa do we consider
- platyhelminthes (flat worms)
- mollusca
- annelida
- acanthocephala
lophotrochozoans are also called
protostomes
do platyhelminthes have a body cavity
no
platyhelminthes (flatworms) are _______ which means they have no body cavity
aceolomate
platyherlminthes (flatworms) can be
predatory and free living, or parasitic or commensals
do platyhelminthes (flatworms) have a circulatory system
no
describe platyhelminthes (flatworm) gut
- simple gut, no anus
- gut (gastrovascular cavity) branches in large forms and ramifies through body
- gaseous exchange across surface
are platyhelminthes (flatworms) motile
yes all motile, although some parasites secondarily sessile
platyhelminthes (flatworms) reproduction
sexual/ asexual
- parasitic species use asexual reproduction because of constraints of life cycle
4 major groups of platyhelminthes
- class turbellaria; free living; marine, fresh water, moist terrestrial
- class monogenea; ectoparasites of fish
- class trematoda; endoparasites (flukes) vet importance
- class cestoda; endoparasitic tapeworms vet importance
turberllaria (class of platyhelminthes)
- mostly free living
- marine, fresh water, moist terrestrial
- some commensal
- some parasitic
- ciliated epidermis for locomotion
- no body cavity; acoelomate
turbellaria excretory system (class of platyhelminthes)
protonephridial; simple system, drains directly from body across wall in excretory vessel
metanephridial excretory system
filtrate is filtered from blood is special filtration sites such as kidney
important model of turbellaria (plathelminthes ie flatworms)
the planarian (dugesia tigrina)
- used to study regeneration and stem cell biology
- can cut worm into many pieces and regenerate entire worm
- generative cell is neoblast; pluripotent cell (can develop into many tissue types)
- models of aging; planarian potentially immortal (has to do w telomeres; caps on the end of chromosomes)
turbellaria vs other classes (monogenea, trematoda, cestoda)
*all platyhelminthes
- turbellaria: mostly free living predatory, epidermis is cellular and ciliated
- other 3 classes; always parasitic/ commensal
- epidermis in larva is ciliated and partly cellular
- epidermis in adults in syncytial (one cell entity but many nuclei) look at pic on slide 23
syncytium
1 cell entity but many nuclei
- syncytial cytoplasm with nucleated cell bodies in parenchyma
(monogenea, trematoda, cestoda)
monogenea (class of platyhelminthes ie flatworm)
obligate ecto-parasites of fish (and rarely aquatic amphibians, reptiles and mammals)
life cycle of monogenea (class of platyhelminthes ie flatworm)
simple
eggs laid, fall of host, hatch, larva seeks new host
characteristics of class monogenea (class of platyhelminthes ie flatworm)
- obligate ectoparasites of fish
- v host specific, will usually only live on one species of fish
- hermaphroditic
- live on skin or gills, when alive transparent but when killed are easy to see
gyrodactylus (example of monogenea; class of platyhelminthes ie flatworm)
very strange and atypical life cycle, doesn’t reproduce, transfers to different fish by contagion, don’t produce many offspring, embryo buds off, so when new worm is born its already carrying its new child (always preggo w a child that is preggo w another) fetus within a fetus
trematoda; flukes (class of platyhelminthes ie flatworm)
- flat leaf like body
- obligatory parasites
- adults live in intestine of vertebrate hosts (usually)
- attach to mucosal wall by suckers
- feed on mucus, tissue fluid, blood
- most hermaphrodite (monoecious)
- complex life cycles w 2 or more hosts
important example of fluke
trematoda; flukes (class of platyhelminthes ie flatworm)
- fasciola hepatica
- liver fluke of sheep, cattle, other grazing animals and humans
- major vet significance
- condemnation of livers
- disease, death
- public health concerns
- present in aus (east coast)
fasciola hepatica life cycle
trematoda; flukes (class of platyhelminthes ie flatworm)
- Sexually mature fluke in sheep (definitive/ final host)
- Eggs pass in host feces (eggs contain miracidium, have trap door in which larva can escape) hatches when it senses freshwater and sunlight
- Larval stages:
- Miracidium: that hatched in water swims and enters snail (intermediate host), they find the snail trails, invade through tissue, become internal parasites of snail
- Sporocysts→ redia→ cercaria by asexual reproduction within the snail
- Cercaria (another type of larva, multicellular looks like a sperm, have a tail) exits snail, looks for freshwater and plant material
- Encystment (metacercaria), forms a cyst on a plant
- Eaten by definitive host (ex sheep or cow)
- Exists in small intestine, move to liver
another important example of fluke
trematoda; flukes (class of platyhelminthes ie flatworm)
- schistosomes
- blood flukes of humans all domestic mammals
- medical significance; 2nd most important parasite after malaria
- vet significance; ovine, bovine schistosomiasis
- unlike fasciola hepatica; dioecious (separate sexes) and active entry to final host (skin, ingestion)
life cycle of schistosomes
trematoda; flukes (class of platyhelminthes ie flatworm)
- mature flukes in blood vessels of intestine
- blood flukes reproduce sexually in human host, fertilized egg exit host in feces
- to get eggs out of host their eggs induce enormous immune response from host which forms a pimple which bursts into intestine so eggs can pass in feces
- People who have this often urinate blood due to this
- eggs develop in water into ciliated larva, larva infect snail
- asexual reproduction in snail results in another type of motile larva
- motile larva penetrate skin and blood vessels of humans
- People infected will suffer from anemia due to blood loss among other effects
cestoda; tapeworms
(class of platyhelminthes ie flatworm)
- parasites of small intestine of vertebrates (high nutrient environment)
- tape like body
- no mouth, digestive tract or anus, nutrients absorbed across body surface
- reproductive system replicated as chain
cestoda (tapeworm) reproductive system and parts
(class of platyhelminthes ie flatworm)
- Scolex- region used to attached to host, has suckers and hooklets, attaches in intestinal crypts of host
- Neck- generation of new proglottids (tunnel like structure, used to describe each of the reproductive units), new proglottids forms at the top by the neck, push the old ones down, they mature sexually as they move down
- Immature proglottids- with respect to reproductive organs
- Mature proglottids- mature male and female organs
- Each proglottids able to generate eggs, produce tons of offspring by replicating their reproductive structures
- Gravid proglottids- egg bearing proglottids, uterus with fertilized eggs; detach break free from chain and pass out in host feces
- Strobila = neck + all proglottids; a few mm to 20cm long
life cycle of beef tapeworm of humans
- human is final/ definitive hosts, live in small intestine
- gravid proglottids breaks free and passes w feces
- eaten by intermediate host cattle
- gets into muscle; infective larva, waits until eaten definitive host (human)
- takes about 12 weeks to grow into adult human
Bladder worm (cysticercus)
larval stage of taenia; occurs in intermediate host, approx 1 cm diameter
Taenia solium
pork tapeworm, adults in humans, bladder worm in pigs in muscle, but this tapeworm can ALSO use humans as intermediate host and invade human muscle, discovered via sudden rise in fireside burns and epilepsy
Echinococcus granulosus
- Hydatid tapeworm; one of smallest cestodes of domestic animals
- Definitive host (harbors adult tapeworm) dog, dingo, fox
- Intermediate host (harbors larval stages) sheep, cow, marsupials, and humans, form macroscopic cysts can be size of baseball, dogs eat the dead humans in africa
- New final host infected by ingesting content of hydatid cyst from raw offal of infected intermediate host
acoelomate
no body cavity, body is solid,
flatworms
coleomate
fluid filled cavity that lied between gut and body wall, lined by mesoderm on both sides,
most complex and large animals have a coelomic cavity
pseudocoelomate
intermediate form of cavity, lined by mesoderm on one side only
nematodes
molluscs are
non segmented lophotrochozoans
annelids are
segmented lophotrochozoans
acanthocephala (phylum of lophotrochozoans)
- strange group of organisms related to rotifers
- 2 host life cycle
- large worms
- parasitic
- arthropod intermediate host
- vertebrate definitive host
- live as adults in small intestine of definitive host
example of acanthocephala (phylum of lophotrochozoans)
- macracanthorhynchus hirudinaceus (= large spiny nosed worm)
- definitive host pigs
- intermediate host is beetles
- no gastrointestinal tract, absorbs nutrients
- proboscis is part that goes into the intestinal lining, have spikes facing backwards to anchor them
life cycle of macracanthorhynchus hirudinaceus
acanthocephala (phylum of lophotrochozoans)
- adult in small intestine of pigs
- separate sexes
- eggs pass w feces
- eggs ingested by beetle larva
- back into pigs (wild pigs not so much domestic pigs)
- proboscis spinous; proboscis penetrates mucosa
phylum mollusca
- lophotrochozoan with body cavity
- non segmented
- distinct mouth and anus
- body cavity= greater complexity
examples of mollusca
- chitons
- gastropods (snails and slugs),
- cephalopods (squid, octopus, etc)
- bivalves
phylum annelida (lophotrochozoans)
- name means little rings
- body cavity and segmented
- includes 3 main groups
- hirudinae; parasitic free living species, includes leeches
- oligochaetes; including earthworms
- polychaetes; fire worm or christmas tree worm
benefits of having a body cavity
- independent movement of body wall and enclosed organs
- more space for complex organs and organ systems; larger size of organism
- storage area for eggs and sperm
- coelomic fluid protects internal organs
- in some animals; circulatory function for oxygen and nutrients to cells
- waste removal
- function as a hydrostatic skeleton
benefits of segmentation
- better control of body sections
- diversification of functions
leech movement
looping movement
