Nematodes Intro Flashcards
What are the niches of nematodes?
most are free-living, so in soil, oceans, hot springs, polar ice
What is the importance of nematodes?
important human and domestic animal parasites, important agricultural pests, biological control agents, Caenorhabditis elegans is non-parasitic and used in research
List some human-parasitic nematodes
ascaris, pinworms, whipworms, hookworms, trichinosis, river blindness, guinea worm, heartworm, filarial worms
Which human-parasitic nematode is most common worldwide?
ascaris: Ascaris lumbricoides
Which human-parasitic nematode is most common in the US/Canada?
pinworms: Enterobius vermicularis
Which species have infectious egg stages?
Ascaris lumbricoides: large, live in small intestines of humans, horses, and pigs. eggs can survive in soil a long time
Enterobius vermicularis: spends entire life in human host, adult infects large intestine. females lay eggs in anus area, causing ithching
Which species have infectious larval stages?
Necator americanus: live in human small intestine, larvae enter host through skin. enters blood, travels to lungs, swallowed in sputum
Trichinella spiralis: in human small intestine. forms muscle cysts and is obtained by eating raw meat
What is the largest nematode and what is it’s host?
Placentonema gigantisma is a couple of meters long and is found in the sperm whale
Describe the overall body shape of nematodes?
non-segmented, elongate, circular but tapered at both ends
What is the nematode body plan?
outermost cuticle, underlying hypodermis, muscle, body cavity
What is the function of the cuticle and hypodermis?
syncitial hypodermis secretes collagen (tough and flexible), proteinaceous (no chitin), no cilia, molted about 4 times before becoming an adult
Describe the muscle layer
only longitudinal muscle (no circular muscle) lies beneath the hypodermis layer so movement is sinusoidal undulating
Describe the body cavity
pseudocoelom, without cilia, filled with pseudocoelomic fluid. organs are located in the pseudocoelom
What are the functions of the pseudocoelomic fluid?
rigidity (hydroskeleton) and transports materials between cells
What are the different components of nematode digestive tract?
mouth, pharynx, intestine, anus
digestive system is complete
intestine has well-developed microvilli
still, most of the digestion is done by the host
Describe the nematode nervous system
a ganglia nervous system with an anterior neural ring (aka circumesophageal nerve ring) with 2 or 4 longitudinal nerves running down the body
Describe the nematode secretory system
two longitudinal excretory ducts that empty from an anterior excretory pore. has 1-2 one‐celled
renette glands. no flame cell
Do nematodes have a respiratory and cardiovascular system?
no. gas diffusion across membrane
How do nematodes reproduce?
are dioecious. females release eggs
Describe the male reproductive organs
smaller than female in size, posterior end is often curved.
single tubule with terminal cloaca and copulatory spicules.
tubular organs increase in diameter as they reach the genital opening
Describe the female reproductive organs
female reproductive organs are paired.
2 threadlike ovaries, 2 oviducts, 2 uteruses, single genital pore at mid-body.
tubular organs increase in diameter as they reach the genital opening
Where do the larval stages occur?
free-living in the soil, or parasitic in either the intermediate or definitive host
What are the different stages of development?
an egg, four larval stages, two adult stages (male and female). sexually immature adults can be called L5
Which stages are pre-parasitic?
egg, L1, L2
Which stages are parasitic?
L3, L4, (L5), adult
What separates each larval stage?
the molting of the cuticle
What does the L1 larva feed on?
bacteria in the external environment
What are the two steps of molting?
synthesis of a new cuticle by the hypodermis (new cuticle develops under old cuticle)
exsheathment, where the old cuticle is loosened and ruptured and the larva wriggles out
Which process initiates infection and why is this?
exsheathment because the larva will not exsheath if it is not in the correct host. it is both host specific and site specific
