Nematodes

Question 1

Why are nematodes and arthropods closely related?

Answer 1

• Both groups have cuticle
• Both undergo ecdysis
• Protostomes
• Ecdysozoans
• Bilateria

Question 2

Nematode body structure

Answer 2

• Pseudocoelomate → false body cavity
• Only one layer of mesoderm → pseudocoel (false body cavity)
• Body under a lot of pressure
• Only have longitudinal muscles (wave of muscles for movement)

Question 3

Nematode cuticle

Answer 3

• Cuticle made of collagen
• Only undergo 4 moults
• 3rd larval stage (3rd moult stage) = dauer
• In parasitic stage dauer is most effective stage
• Cuticle covered in glycocalyx - glands
• Some diffusion takes place over the surface of the cuticle
• Epidermis secretes cuticle
• No circulatory system → rely on diffusion across the cuticle

Question 4

Nematode: Digestion

Answer 4

Oesophagus - mouth part like a pump with strong muscles
Buccal cavity (modified depending on species and what they feed on)

Question 5

Nematode: Excretion

Answer 5

Excretory canal
Osmoregulaiton

Question 6

Nematode: Reproduction

Answer 6

• Dioecious
• Internal fertilsation
• During mating - males sense females using chemical queues
• Use spicule to force open female opening
• Sperm cant swim
• Female show some sort of female choice

Sex determination can be chromosomal or environmental → plenty of food available tend to be females (females are larger so need more food etc)

Question 7

Nematode: Sensory Sensilla

Answer 7

detect chemical queues, heat pain, etc

Question 8

Parasitic nematodes: Pin worm

Answer 8

• Live in human gut
• Female lays eggs in host anus at night
• Causes itching and transfers eggs via scratching
• Eggs are ingested by another individual
• Cycle begins again

Question 9

Parasitic nematode: Hookworm

Answer 9

• Feeds on intestine of host and causes blood loss
• Larval stage 3 - infection stage
• Lavae hang around in vegetation etc
• Larvae penetrate into human body
• Migrate around body via blood stream
• Go to heart then lungs → irritate lungs causing host to cough → they cough up worms and are then swallowed into the gut

It is belived this migration allows larger size and thus the species becomes more fecund. (produces more offspring).

Question 10

Parasitic nematode: Guinea worm

Answer 10

• Lives in body cavity / connective tissue of human host
• Migrates to surface of skin forms ulcer and releases larvae
• Larvae consumed by crustacean called copepod (tiny) at larval stage 3 (most infective stage)
• Can be taken back up by humans if water isn’t filtered

Traditionally extracted by being wound around a stick

Question 11

Parasitic nematode: Filarial nematode

Answer 11

• Inhabit the lymphatic system of humans
• Can live there for 10-18 years
• Can cause elephantiasis
• Part of their lifecycle is within a mosquito

Found in blood system at certain times of the day → links with mosquito feeding times

Question 12

Parasitic Nematodes

Answer 12

• Parasitism evolved several times
• Parasitic as juviniles, adults or both.
• Can have one or more intermediate host
• Radiation accompanied insects, amnotic vertebrates and flowering plants

Question 13

How nematodes affect host behaviour?

Answer 13

Alter shrimp behaviour so they are more likely to be eaten by sandpiper

Sandpiper is nematodes final host

Question 14

What is the relationship between nematodes and Wolbachia (bacteria)?

Answer 14

• Symbiotic relationship
• Bacteria provide chemicals for reproduction and survival
• Some nematodes can be treated with antibiotics due to this relationship