Nematodes Intro

Question 1

What are the niches of nematodes?

Answer 1

most are free-living, so in soil, oceans, hot springs, polar ice

Question 2

What is the importance of nematodes?

Answer 2

important human and domestic animal parasites, important agricultural pests, biological control agents, Caenorhabditis elegans is non-parasitic and used in research

Question 3

List some human-parasitic nematodes

Answer 3

ascaris, pinworms, whipworms, hookworms, trichinosis, river blindness, guinea worm, heartworm, filarial worms

Question 4

Which human-parasitic nematode is most common worldwide?

Answer 4

ascaris: Ascaris lumbricoides

Question 5

Which human-parasitic nematode is most common in the US/Canada?

Answer 5

pinworms: Enterobius vermicularis

Question 6

Which species have infectious egg stages?

Answer 6

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

Question 7

Which species have infectious larval stages?

Answer 7

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

Question 8

What is the largest nematode and what is it’s host?

Answer 8

Placentonema gigantisma is a couple of meters long and is found in the sperm whale

Question 9

Describe the overall body shape of nematodes?

Answer 9

non-segmented, elongate, circular but tapered at both ends

Question 10

What is the nematode body plan?

Answer 10

outermost cuticle, underlying hypodermis, muscle, body cavity

Question 11

What is the function of the cuticle and hypodermis?

Answer 11

syncitial hypodermis secretes collagen (tough and flexible), proteinaceous (no chitin), no cilia, molted about 4 times before becoming an adult

Question 12

Describe the muscle layer

Answer 12

only longitudinal muscle (no circular muscle) lies beneath the hypodermis layer so movement is sinusoidal undulating

Question 13

Describe the body cavity

Answer 13

pseudocoelom, without cilia, filled with pseudocoelomic fluid. organs are located in the pseudocoelom

Question 14

What are the functions of the pseudocoelomic fluid?

Answer 14

rigidity (hydroskeleton) and transports materials between cells

Question 15

What are the different components of nematode digestive tract?

Answer 15

mouth, pharynx, intestine, anus
digestive system is complete
intestine has well-developed microvilli
still, most of the digestion is done by the host

Question 16

Describe the nematode nervous system

Answer 16

a ganglia nervous system with an anterior neural ring (aka circumesophageal nerve ring) with 2 or 4 longitudinal nerves running down the body

Question 17

Describe the nematode secretory system

Answer 17

two longitudinal excretory ducts that empty from an anterior excretory pore. has 1-2 one‐celled
renette glands. no flame cell

Question 18

Do nematodes have a respiratory and cardiovascular system?

Answer 18

no. gas diffusion across membrane

Question 19

How do nematodes reproduce?

Answer 19

are dioecious. females release eggs

Question 20

Describe the male reproductive organs

Answer 20

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

Question 21

Describe the female reproductive organs

Answer 21

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

Question 22

Where do the larval stages occur?

Answer 22

free-living in the soil, or parasitic in either the intermediate or definitive host

Question 23

What are the different stages of development?

Answer 23

an egg, four larval stages, two adult stages (male and female). sexually immature adults can be called L5

Question 24

Which stages are pre-parasitic?

Answer 24

egg, L1, L2

Question 25

Which stages are parasitic?

Answer 25

L3, L4, (L5), adult

Question 26

What separates each larval stage?

Answer 26

the molting of the cuticle

Question 27

What does the L1 larva feed on?

Answer 27

bacteria in the external environment

Question 28

What are the two steps of molting?

Answer 28

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

Question 29

Which process initiates infection and why is this?

Answer 29

exsheathment because the larva will not exsheath if it is not in the correct host. it is both host specific and site specific