Platyhelminthes Flashcards
Two major evolutionary advances of plathyhelminthes
⚬ Cephalization
⚬ Primary bilateral symmetry
General Features of plathyhelminthes
- Mesoderm well-defined
- Triploblastic
*Highly specialized parasites - Some argue this group were derived from complex
free-living organisms
having a body derived from three embryonic cell layers
Triploblastic
the concentration of sense organs, nervous control, etc., at the anterior end of the body, forming a head and brain, both during evolution and in the course of an embryo’s development.
Cephalization
Typical animals that have only one internal space, the digestive cavity
Acoelomates
- Commonly called flatworms
- Vary from a millimeter to many meters in length
- Some free-living; others parasitic
Phylum Platyhelminthes
Platyhelminthes is divided into four classes:
Class Turbellaria
Class Trematoda
Class Monongenea
Class Cestoda
Class
⚬ Mostly free-living
⚬ Range from 5 mm to 50 cm long
⚬ Except for polyclads
Simple gut or no gut and a simple pharynx
Class Turbellaria
free-living in Class Turbellaria Except for
polyclads, endolecithal
turbellarians
Class Turbellaria organisms that have a folded pharynx and a gut with many branches
Polyclads
Class Turbellaria is a Member of
Tricladidia
are parasitic flukes
Most adults are endoparasites of vertebrates
They resemble ectolecithal turbellaria but the tegument lacks cilia in adults
Sense organs are poorly developed
Class Trematoda
Adaptations for Class Trematoda parasitism include:
⚬ Hooks and suckers for adhesion
⚬ Increased reproductive capacity
Phylum Platyhelminthes
* Adult fluke lives in bile passageways in the liver of sheep and other ruminants
* Eggs are pass out in feces
Fasciola hepatica (Sheep Liver Fluke)
Phylum Platyhelminthes
In Fasciola hepatica (Sheep Liver Fluke), the ____ hatch and penetrate snails to become sporocysts
Miracidia
two generations of rediae
Cercaria
metacercariae
stage that encyst on vegetation and await being eaten by sheep in Fasciola hepatica (Sheep Liver Fluke),
Cercaria
stage that develop into young flukes
in Fasciola hepatica (Sheep Liver Fluke),
metacercariae
Phylum Platyhelminthes
* Most important human liver fluke
* Common in China, Japan, and Southeast Asia
* Also infects cats, dogs, and pigs
* Adult fluke is 10–20 mm long with an oral and ventral sucke
Clonorchis sinensis: Chinese Liver Fluke
Clonorchis Life Cycle
- Adults live in bile passageways of humans and other fish-eating mammals
- Eggs containing a complete miracidium are shed into water with feces
- The eggs hatch only when ingested by snails of specific genera
- Miracidium enters snail tissue and transforms into a sporocyst
- Sporocyst produces one generation of rediae, which begin differentiation
Phylum Platyhelminthes
Over 200 million people infested with schistosomiasis
Common in Africa, South America, West Indies, and the
Middle and Far East
* Sexes are separate
Schistosoma: Blood Flukes
- 3 species account for most human schistosomiasis
⚬ S. mansoni in venules of large intestine
⚬ S. japonicum in venules of small intestine
⚬ S. haemotobium in venules of urinary bladder
Schistosoma Life Cycle
- Eggs discharged in human feces or urine
*In water, eggs hatch as ciliated miracidia - Must contact a particular species of snail to survive
*In the snail, they transform to sporocysts - Sporocysts produce cercaria directly
- Cercariae escape the snail and swim until they contact bare human skin
- Cercariae pierce the skin and shed their tails
- Enter blood vessels and migrate to the hepatic portal blood vessels
- Develop in the liver and they migrate target sites
- Eggs released by females are extruded through gut or bladder lining and exit with feces or urine
Eggs that remain behind become centers of inflammation in Schistosoma
Trues
Phylum Platyhelminthes
that parasitizes humans, pigs, rodents, etc.
Eggs are coughed up in sputum, then swallowed and eliminated in feces
Human infection occurs by eating uncooked crabmeat
Paragonimus westermani: Lung Flukes
Metacercariae of Paragonimus westermani: Lung Flukes develop in
freshwater crabs
Cercariae of Paragonimus westermani: Lung Flukes shed into the water and ingested by
freshwater crabs
Paragonimus westermani: Lung Flukes Life Cycle
*Eggs are coughed up in sputum, then swallowed and eliminated in feces
*Zygotes develop in water and miracidia penetrate a snail host
*Within the snail, miracidia give rise to sporocysts, which develop into rediae
* Cercariae are shed into the water and ingested by freshwater crabs
* Metacercariae develop in freshwater crabs
*Human infection occurs by eating uncooked crabmeat
Monogenetic flukes
were originally placed in Trematoda
External parasites of fish especially gills, but a few are found in bladders of frogs and turtles
Have direct life cycle in a single host
Class Monogenea
- Some now argue they are sister taxa, Trematoda and Monogenea having a posterior attachment with hooks
true
Class Monogenea
part that attaches to host by posterior hooks
Oncomiracidium
Class Monogenea
Posterior hooks may become the posterior attachment organ of the adult, the
vary widely (hooks, suckers, clamps)
Withstand the force of water flow
Some serious economic problems in fish farming
opisthaptor
have long flat bodies with scolex
Lack a digestive system
Muscles, excretory and nervous systems similar to other flatworms
Lack sensory organs except for modified cilia
Class Cestoda
Tapeworms
Class Cestoda
Holdfast structure with suckers and hooks
scolex
Class Cestoda
Scolex is followed by a linear series of reproductive units or
proglottids
Class Cestoda
the long body of the Tapeworms
strobila
Class Cestoda
* Lives as an adult in the alimentary canal of humans
* exists in beef
* Mature adults can reach over 10 meters in length with over 2000 proglottids
* Scolex has four suckers but no hooks
Gravid proglottids pass in feces
*no suckers
Taenia saginata: Beef Tapeworm
Taenia saginata: Beef Tapeworm
*Juvenile form found in
intermuscular tissue of cattle
each segment in the strobila of a tapeworm, containing a complete sexually mature reproductive system.
proglottids
segment that contains uterine branches filled with eggs, or shelled infective larvae
Gravid proglottids
Taenia saginata Life Cycle
- Cattle swallow shelled larvae that hatch as oncospheres
*Oncospheres use hooks to burrow through the intestinal wall into blood or lymph vessels - When they reach voluntary muscle, they encyst to become bladder worms (cysticerci)
- When the infected meat is eaten, the cyst wall dissolves and the scolex evaginates to attach to intestinal mucosa
*New proglottids develop in 2–3 weeks
*Infected individuals expel numerous proglottids daily
*Infection can be avoided by eating only thoroughly cooked beef
Phylum Platyhelminthes
* Adults live in small intestine of humans
* found in pork
* Scolex has both suckers and hooks on the
rostellum
Taenia solium: Pork Tapeworm
Phylum Platyhelminthes
*Juveniles live in muscles of pigs
Taenia solium: Pork Tapeworm
If eggs or proglottids of Taenia solium: Pork Tapeworm are ingested
what happens
⚬ Embryos migrate to organs and form cysticerci
commonly occurs in eyes or the brain blindness, serious neurological symptoms or death, caused by Taenia solium: Pork Tapeworm
Infection can be avoided by eating thoroughly cooked pork
Cysticercosis
Phylum Platyhelminthes
Adults found in intestines of humans, dogs, cats and other mammals
Immature stages found in crustaceans and fish
Largest cestode of humans, reaching up to 20 meters in length
Diphyllobothrium latum: Fish Tapeworm
Phylum Platyhelminthes
- Adults parasitize dogs and other canines
*Juveniles infest many mammals
*Humans may serve as intermediate host - Main cyst maintains a single chamber
⚬ Daughter cysts bud off with thousands of
scolices, each able to produce a worm if
eaten - Surgical removal is the only treatment
Echinococcus granulosus: Unilocular Hydatid
Echinococcus granulosus: Unilocular Hydatid Juveniles are a special cysticercus, a hydatidcyst, that grows for up to
20 years
Neodermatans are composed of
trematodes, monogeneans, and cestodes
taxon Turbellaria is paraphyletic
true
Neodermatans form a monophyletic group
true
Allied with trematodes, monogeneans, and cestodes as the sister group to endolecithal turbellarians
Ectolecithal turbellarians
phylum
Considered a “missing link” between protozoa and metazoa
Have a simple level of organization
Minute, ciliated, and wormlike animals
Phylum Mesozoa
Phylum Mesozoa All live as parasites in
marine invertebrate
Phylum Mesozoa
Most composed of only ________ cells arranged in two layers
Layers are not homologous to germ layers of other metazoans
20 to 30
Phylum Mesozoa
Two classes
Rhombozoa and Orthonectida
Phylum Mesozoa
* Live in kidneys of benthic cephalopods
*Inner, reproductive cells give rise to vermiform larvae
* When overpopulated,reproductive cells develop into gonad-like structures producing male and female gametes
* Larvae are shed with host urine into the seawater
Rhombozoans
Rhombozoans
Adults called ________ and are long and slender
vermiforms
Phylum Mesozoa
* Parasitize variety of invertebrates
* Reproduce sexually and asexually
* plasmodium
Orthonectids
Orthonectids
Asexual reproduction consists of a multinucleated mass called a
plasmodium
Some consider these organisms primitive flatworms and place them in phylum Platyhelminthes
Molecular evidence groups Phylum Mesozoa with flatworms in
superphylum Lophotrochozoa
orthonectid and two species from a rhombozoan subgroup, the dicyemids, did not show members of the two classes to be
sister taxa
Phylum Mesozoa may not be monophyletic
true
*Often called ribbon worms
*Have a long muscular tube, the proboscis
*Over 1000 species
* Most are less than 20 cm long
*General body plan similar to that of turbellarians
* Epidermis is ciliated with many gland cells
* Excretory system has flames cells; several have rhabdites
* Mostly dioecious
Phylum Nemertea
long muscular tube in Phylum Nemertea
proboscis
Phylum Nemertea
wjay is the shape of their pilidium larva
Helmet-shaped pilidium larva
- Adult has an anus, producing a complete digestive system that is more efficient
- Simplest animals with a blood-vascular system
- Most are marine
⚬ Some are found in moist soil and freshwater - Few are commensals or parasites
Phylum Nemertea
Ventral mouth but no anus resembling flatworms and trochophore larvae of annelids and molluscs
pilidium larva
regenerate readily
* Some fragment themselves during certain seasons
* Tail sections can regenerate a new proboscis within a short time
Phylum Nemertea
Phylum Nemertea Classes
Class Enopla
Class Anopla
Phylogeny of Nemertea
- Much debate about the phylogenetic position of nemerteans
- Larval forms vary
*Nemertean body plan is controversial - Are they coelomate or acoelomate?
