Cestodes Intro Flashcards
What are some defining features of cestodes?
obligate parasites, entirely endoparasitic, no mouth or digestive tract, each proglottid has male and female sex organs (hemaphroditic)
What are some features of the cestode life cycle?
no asexual phases, at least one intermediate host is required
What types of animals are usually definitive hosts?
hunters
What types of animals are usually intermediate hosts?
the prey of hunters
can be a mammal, an arthropod, a fish, a bird, a reptile
What are the three distinct parts of a cestode body?
scolex, neck, strobila
What is the difference in the scolex of the order Pseudophyllidea and Cyclophillidea?
Pseudophyllidea: scolex has slit-like suckers/grooves
Cyclophillidea: scolex contains suckers and sometimes hooks
How can most tapeworms be distinguished?
by looking at the scolex
What are some features of the neck?
undifferentiated and unsegmented, the narrowest part of the body, where new proglottids differentiate
Define strobilization?
the synthesis of new proglottid segments from the neck so that the strobila becomes longer.
proglottids at the posterior end become more sexually mature
What are the three types of proglottids?
immature proglottid (newly synthesized) mature proglottid (have male and female sex organs) gravid proglottids (develop after mating. have hundreds of embryonated eggs)
What happens to gravid proglottids in the host?
male and female organs disintegrate as they are replaced with eggs, gravid proglottids detach from the strobila, and are either released in the feces intact or disintegrated to release the eggs
What are the male sex organs?
many testes, vasa differentia, vas deferens (often highly coiled), cirrus sac with cirrus, common genital pore
What are the female sex organs?
two ovaries, vitellaria (yolk gland), mehlis’ gland, uterus, vagina, common genital pore
How do cestodes fertilize their proglottids?
self-mating within a segment is rare
sperm usually transferred to adjacent mature proglottids
each gravid proglottid can contain 100-1000’s of eggs
What are some common characteristics of cestode eggs?
- passed eggs are always embryonated
- contain an oncosphere, which is encased in an inner evelope, which is surrounded by an embryophore. The outer envelope surrounds this and is covered by the shell/capsule
- can remain in external environment for weeks to months
What is particular about the tegument of cestodes?
because they have no digestive tract, tegument also absorbs nutrients and must resists digestive enzymes of the host.
This is accomplished by the glycocalyx (carbohydrate-based) layer. there are many villi to increase surface area also
What is the syntegument?
outer anucleate syncytial cytoplasmic layer containing mitochondria and secretory bodies
What is the cytotegument?
nucleated cell bodies lying beneath the tegumental muscles and attached to the syntegument
How do cestodes digest their food?
they do not secrete digestive enzymes. they rely on their host to do this for them. their tegument has evolved to competitively absorb host nutrients such as amino acids, sugars, fatty acids, purines, pyrimidines and vitamins
How do cestodes respond to various osmotic pressures?
they have no control over their body volume: they swell in dilute solutions and shrink in concentrated solutions.
they appear to be slightly hypotonic to their surroundings
Describe the cestode nervous system
paired ganglia in scolex, with nerves running down the body and forming a ladder-like shape.
the scolex features are richly innervated
