Platyhelminths Flashcards
What does platyhelminths mean? And what is it commonly known as?
Latin for flat dorsoventrally
Known as flatworms
Make up sinplest worm-like animal group among multicelular metozoans
Platyhelminths are _______ and _____ symetrical
Acoelomate
Bilaterally
Platyhelminths have how many germ layers?
Tripoblastic
-mesoderm layer of embryo is composed of loosed cells (parenchyma tissue), filling the space between ectoderm and endoderm
_____ platyhelminths are parasitic
3/4 or 80%
And 1/4 is free living
What is the free living class of playhelminths
Turbellaria
Most primitive
Development of playhelminths
Protostome-like; first opening is mouth which forms from the blastophore. No anus
Platyhelminths feeding
Feeding is through the only single opening; and wastes not metabolised leave through the same pore (no anus like cnidarians)
-carnivorous typically
Platyhelminths lack which systems
What is used instead?
Respiratory and circulatory; fee have hemoglobin
-gas exchange with the external environment is by simple diffusion via body surface; depending on oxygen concentration graduent across the ectoderm, its permeability to gas, thickensss and surface area
Thus, flat body surface allows sufficient gas exchange
What type of clevage is in platyhelminths
Spiral
Determinate in some
Do playhelminths have a brain?
Most possess a brain, connected to a pair of longitudinal nerve cords
Advanced soecies possess a par of nerve cords, ventrally positioned
Protonephridia
Solenocytes
(First kidney/ flame cells) in platyhelminths used for excretion.
Group of specialized cilia like cells forming like a cup with fine mesh.
Solenocytes
Some platyhelminths have this type of protonephridium) having flagella in the cup like mesh instead if cilia
All forms of protoenphridia function as _____
Osmoregulators (water abd salt balance) and getting rid of metabolic wastes like urea, ammonia and amino acids
Hermaphrodites
All platyhelminths are hermaphrodites. Generally no self fertilization, except fee like Schistosoma sp.
(Both kinds of reproductive organs)
4 main classes of platyhelminths
Turbellaria (free-living)
Cestoda
Monogeneans
Trematoda
Turbellaria class differentiation
Only free living class among 4 classes, 4500 are free living, 150 are either commensal or parasitic in other invertebrates
Parasitic group hypothesized to evolve from a different ancestor than free living, which evolved frim neodermata
15% of platyhelminths
Class turbellaria size
Average length is 1cm, could be longer in aquatic species
Turbellaria nervous system
Nervous system is a diffuse nerve net, similar to cnidarians; could be advanced to form a cerebral ganglion (primitive but distinct brain, found in parasitic group)
Turbellaria class have a high rate of ____
Dehrydration , due to high surface area
Turbellaria habitat
Most are aquatic, mostly marine, fee freshwater, fee terestrial but under humid conditions
-most aquaitc species are benthic (bottom of ocean)
Turbellaria body
- body is ciliated (more on ventral side)
- each epidermal cell is multiciliated (several or many cilia) compared to monocialiated poriferans and cnidraians)
- pssess one or more pair of eyes at anterior end along with fells for detecting stimuli like chemical (food), pressure (water current) and mechanical
Turbellaria locomotion
- locomotion i sby means of muscular contraction wave along the ventral side (anterior to posterior); unidirectional.
- possess circular muscle (forward movement); and longitudinal muscle-contract and move the worm in its desired direction reffered to as looping
Turbellaria possess ____ glands
Duo
Paired gland which secrete glue-like substance at body surface ir temporary attatchemnt
Turbellaria Rhabdoids
Aggregate of small, cylindrical structures surrounding the body surface of turbellarians which release mucus for avoiding predation or dehydration
Food of turbellaria
Typcially carnivarous; some are dentritus and algae feeders; some harbour symbionts with algae
Turbellaria digestion
In two phases
- Extracellularly by digrstive enzyme
- Intracellularly following ohagocytosis of the food particle
Digedtive system of turbellaria
Very simple digedtive system, varies among species
- simple mouth on ventral surface
- no or partially formed guy cavitt (acoela)
- in acoela, food is stored in a central cavity (no gut)
Most acoela are ______
Marine (resemble planula larvae of cnidraians)
Acoela are thought to be ancestors of tripoblastic animals
Turbellarians possess varying gut complexity….
3
- branched
- straight
- multi-branched
Mouth of complex species is opening through a protruisble pharynx
Turbellaria reproduction
- Haemaphrodites (male and female organs) though male is more complex
- in triclad species, two individuals extend the male organ into opposite femsle genitals and exchange sperm
- in other turbellarians, copulation by hypodermal impregnation can occur where the penis stylet penetrate the body of the second work leading to fertilization of opposite eggs; the resulatnt young worm develop in a protectivr capsule.
- no free living larva stage (planula)
Some marine turbellaria embryos develop a tiny-short-lived free swimming larva known as _____
MULLER’s Larva
Turbellaria regeneration
Very high regenerative potentials controlled by the neoblast (undifferentiated cells, restricted to turbellarians)
Class Cestoda unique characterisics
Platyhelminths
- Scolex (organ of attachment); small anterior hooked organelle
- Proglottids
- Lack of digestive system
Endoparasite
Class cestoda
-live attached to host intestine for nutrient; cause disease in over 135M people worldwide
Non-ciliated tegument
Class Cestoda
With syncytial (multinucleated): increases surface area of the tegument for nutrient uptake
Cestoda class have no ____ instead they have
Mouth
Scolex, suckers or hooks (for attachment)
Where is the neck of cestoda
Betwen the scolex and body segments (prolottids)
Neck is where new segments are added, newest segment is closest anteriorally)
Sub classes of Cestoda
Cestodaria
Eucestoda (true cestodes or tapeworm)
Subclass Cestodaria
- lack gut and are endoparasites of fish and turtle
- lack scolex and external segmentation (proglottids)
- 10 hooks in larva stgae
- only one set of male and female organs
- greatest length is 35cm
Ex: Amphilina and Gyrocotyle
Subclass Eucestoda
- presence of scolex suckers snd proglottids
- 6 hooks in larva stage
- up to 20m
- endoparasites of verioue invertebrates, reptiles, rodents, burds and mammals (including human)
Ex: Taenia solium, Hymenolepis diminuta
-cause chronic infection: dont cause enougj damage to host, so they can use host longer.
Subclass Eucestods
Neck
Strobili
Length
Neck: between the scolex snd body segments (proglottids)
Strobili: whole region of the proglottids (unripe, matured and ripe (gravid)
Length: length between few centimeters to 2 m
Cesotda reproduction
- haemaphrodites
- each segment bears numerous male testes (1000) and female ovaries (50000) organelle
- self or cross fertilization between proglottids of the same work or between proglottids of different worms.
- an individual may contain 2000-4000 proglottids; implying that 10,000-100,000 fertilized eggs are released per day through feces into the envrionment
- transmission mainly trhoigh fecal - oral route
- released eggs: proglittids in feces may contaminate hands leading to infection
Cestodes are endoparasites and their life cycle may be______ or ____
Direct (no intermediate host)
Indirect (imediate host ex: Taenia solium; cattle-Taenia saginata
Direct lifecycle of cestode
Fertilized eggs are released via the intestine in feces which contaminate hands/ fruits and vegetables. Ingested eggs hatch in the intestine and develop into adult.
Indirect lifecycle of cestode
Fertilized eggs released theough feces are ingested by intermediate host (cattle or pig) and hatch in the stomach to become an onchosphere larvae
Onchosphere larvae have ____
Hooks, flame cells, muscles and able to digest through the wall of intedtine and form cysts in the host muscle wall
(Cestoda)
Encystment in Taenia species may form
Bladder worm; while in other soecies may replicate asexually to form hydatid (deadly)
Block and cause malfunctions if in brain
Humans (definite host) become infected by consuming
Undercooked pork or beef containing encysted parasites, which hatch in the intestine
(Cestodes)
Prevention of cestodes
Cooking beef or pork before consuming or freezing to very low temperatures
Class Monogeneans unique body characteristics
-possess posterior attatchment oragan (Haptor; posterior=opistophaptor), suckers, complex hooks for attatchment and sclerites
Larval stage of monogeneans
Called oncomiracidium with 3 bands of cilia, with one or two pairs of eyes.
Are monogeneans parasites?
Yes, most are ectoparasites (external); some are endoparasites (internal): external parasites attach to hosts by suckers, hooks and attachment organs opistohaptor abd prohaptor (anterior attachment organs with suckers and hooks
Few are endoparasites: Polystoma sp.
Infect variety of vertebrate aniamls like amphibians, fish and reptiles
Lifecycle of monogeneans
Direct: no intermediate host
Sexually matured adult—>egg laying—>hatch into larvae—>attatchment to fish
Diversity of monogeneans
Choricotyle louisianensis; parasite of gill of fish
Polystomoidella oblongum; parasite of the urinary bladder of turtles
Entobdella soleae; oncomiracidium larve
Which species of platyhelminths have the highest species diversity
Monogeneans
Evolutionary relationship of Monogeneans
Close evolutionary relationship with Cestodes and trematodes
All members of monogeneans are secually classified as______
Haemaphrodites
2 suborders of Monogeneans
Monopistocotylea: one haptor; ecto and endo parasites of fish, copepod, amphibains
Polyopistocotylea: have two or more haptors (branched); ectoparasite of fish, endoparasite of amphibians, most are blood feeders
Class Trematoda (flukes)
- parasidic?
- unique parasite characteristics
All parasites (endoparasites) and sexual matuity is attained in vertebrate hosts
Possess oral and vebtral sucker and hooks
Parasitic lifecycle of Trematoda
- reproduction occurs in definite host
- fertilized eggs/ embryo are passed out of host either stool or urine
- identify, and attach to suitable hosts
- entry/ penetration of host
- navigate to suitable organs and tissues in hosts and establish a position within the host
- adapt to low oxygen internal environment of the host (anaerobic respiration)
- establish a chronic infection (induce minimal harm to host)
- avoid and manipulate the hosts immune system
Class Trematoda body characteristics
- Tegument: unciliated multinucleated (Syncytial)
- Lack of body segmentation: like turbellarians; unlike cestodes
- possess mouth (oral sucker) for getting nutrients from hosts
- flattened dorsoventrally
- most are haemaphrodites
- high fecundity (offspring rate)
Trematode classification
2 sub classes
- Digenean (two birth)
- abundant (6000 species)
- most members are endoparasites
- lifecycle of most members reauire 2 or more hosts - Aspidogastrean (100 species)
Digenean lifecycle
- at least 1 intermediate host to reach definite host (vertebrate)
- lifecycle an active process (unlike cestodes)
- adults produce eggs into enveionment through urine or feces, usually end up in water.
- eggs hatch into free swimming ciliated larva (miracidium)
- Miracidia species specific, strive to gain access into an intermediate host (molluscs) or consumed
- asexual multiplication into mother and daughter sporocyst before becoming a radiae (active feeders)
- radiae house numerous larvae; migrate to hosts digestive system or gonad and develop either into an encysted larvae (metacercariae) or free swimming (cercariae)
- carcariae emerge from snails to infect a definite (vertebrate) host by skin penetration
- metacercariae attach to vegetation waiting to be consumed by definite host
Schistomiasis
A parasitic infection caused by digenetic blood flukes of the family Schistosomidae
- water related disease and is transmitted by fresh water snails infected with cercariae of the parasite
- infection ocurs through man contact with larvae-infested waters
Blood fluke=resides in blood
Who discovered Schistosomiasis
Theodore Bilharz, hence it is also reffered to as Bilharziasis or snail fever
How many known Schistosome species infect humans?
8 5 are commin 3 are of major health importance -S. haematobrium -S. japonicum -S. mansoni -S. intercalatum -S. mekongi
Early manifestations of Schistosomiasis
- skin rash a week later
- decended and enlarged abdomen caused by enlarged liver and or spleen (hepatosplenomegaly)
Risk factors of Schistosomiasis
- occupational activites performed by males in infested water bodies
- recreational activities by males which increase their chances of being infected
Highest prevalence and intensities of infection of Schistosomiasis
Young adolescents 60-80%
20-40% of adults
Prevention of Schistosomiasis
- avoid contact with infected fresh water
- use protective shoes in infested water
- adhere to parasite warnings
- avoid indiscriminste disposal of fecal waste
- fine-mesh filters csn be used to filter the cercariae
- preventive chemotherapy as a strategy for morbidity control
Opisthorchis sinensis
Fasciola hepatica
Chinese liver fluke infecting humans
Sheep liver fluke
Lifecycle of Diceocoelium dendriticum
Trematode
- lifecycle occurs only on land
- two intermediate hosts (labd snail and ant)
- cattle is definite host
- no redia stage (daughter sporocyst) that gives rise to cercariae
- eggs released by infected cattle in feces lie on soil or vegetation, waiting to be eated by appropriate snail.
- Miricadium hatches from an egg and develop into carcariae in snails
- cercariae are bathed in snials mucus and migrate to snails lungs, where they are expelled in slime balls to environments vegetation
- ants pick up cercariae in slime balls which encyst as metacercariae in the brain of ants, there metacercariae manipulate the ant to settle on grass blades during morning or evenings which coincides with cattle grazzing.
- metacercariae wall are digested in small intestine releasing adult in bile duct snd gall bladder
Subclass aspidogastrean unique characteristics
- possess large ventral sucker separated by septa; forming rows of suckers
- smallest group of platyhelminths
- 80 species
- resemble monogeneans and digeneans
Hosts of Aspidogastrean
Single host usually are mollsucs, especially gastropods and fresh water mussels
Some species require an intermediate host (molluscs) and reaching adult hood in fish or turtles (definite host), resembling the trematodes, but differ with lack of asexual reproduction
