Nematodes

Question 1

Nematode features

Answer 1

Ecdysozoa - moult
Pseudocoelomates
Have cuticle - helped with success
Cuticle of collagen and other protein with cross-links - tough but still flexible
4 moults in total - reach adult, which grows slightly so cuticle more flexible than arthropods

Question 2

Pseudocoelomates and the impact this has

Answer 2

Outer layer of ectoderm
Inner layer of endoderm surrounding gut
One muscle layer on inner side of ectoderm
-no second layer lining endoderm
Not a proper body cavity - pushed on by muscle layer which squashes gut = lots of pressure
Whole body revolves around this pressure

Question 3

Structure of nematodes

Answer 3

Tapered at both ends
Muscle blocks/cell are longitudinal - move with undulations
Gut squashed by high pressure
Cuticle is secreted by epidermal layer
Excretory canal (thought of as protonephridium, now in osmoregulatory control)
-controls salts and water levels
Strong muscles at entrance and exit to gut so food not forced out
Nerve ring at head like brain - nerve cord down animal

Question 4

Types of nematode head

Answer 4

Bacteriovore - not massively specialised
Plant root cell predator - stylet which puncture the plants
Feeds on protozoans and small animals have teeth
Hook worm parasite has teeth in hook form
All have strong musculature in mouth

Question 5

Reproduction

Answer 5

Dioecious mainly - some hermaphrodites
Internal fertilisation - due to high pressure of body can cause problems
-M has spicule to keep reproductive opening open
-sperm have no flagella as cannot swim against pressure (they crawl)
F larger than M
Sex determined environmentally - more food = bigger = F

Question 6

Parasitic nematodes

Answer 6

Evolved several times
Radiation accompanied by flowering plants, insects and amniotes
Parasitic as…
juveniles only
adults only
all their life
Can have intermediate hosts, or rely on reinfection from contaminated individual

Question 7

Migratory parasitic nematode example

Answer 7

Loa loa - African eye worm

Lives in subcutaneous tissue and will migrate beneath the conjunctiva (mucous membrane at from of eye)

Question 8

Plant nematodes

Answer 8

Root knot nematode
Global problem - crashes economies
1. Makes way to root system causing galls to form where they will live
2. Will drain away photosynthetic products of plants and nutrients they take up
3. Root system and plant overall not as effective

Question 9

Nematode host manipulation

Answer 9

Crustacean intermediate - makes them swim near surface in day when sandpiper is feeding
Ant intermediate - infection in abdomen caused it to become red and berry-like so final host is attracted to it and eats it

Question 10

Enterobius

Answer 10

3/4 of worlds population infected - only humans

1. Primarily infects children - female has fertilised makes way to host anal region at night, lays eggs there
2. Causes itching in child - scratches lead to eggs dispersed onto bed clothes, sheets, fingers etc.
3. Eventually eggs mature
4. Re-infestation (child sucks finger or deposits eggs to other places) into new host through ingestion
5. Hatch and mature in intestine - begins again

Question 11

Hook worm

Answer 11

Indirect cycle - 1 human host

1. Female will be fertilised by male and release eggs in human faeces - poor sanitisation etc.
2. Eggs develop and hatch into larval stage
3. Larvae penetrate through human feet
4. Make way into circulation - heart - lungs - trachea
5. In trachea makes individual caught them up and into oesophagus where swallowed
6. Larvae mature in intestine - rasping away at wall to feed on blood and body fluids

Question 12

Ascaris

Answer 12

Large nematode group also found in other vertebrates

1. Areas of poor sanitation - eggs transmitted in faeces
2. Eggs swallowed and burrow through gut into blood system
3. Make way to heart, to lungs
4. Coughed up and swallowed - mature where matures into reproductive form
5. Numbers leads to blockage of gut and various other places - leads to death

Question 13

Dracunculus

Answer 13

Guinea worm can reach 120cm
1. Female fertilised like subcutaneous tissue
2. Form an ulcer on skin when ready to release eggs
3. Gives people desire to go into water and relieve pain
4. Larvae released in water
5. Makes way to copepod (intermediate)
6. If taken up by drinking water (human) worm develops in human gut and repeats
Removal by winding around stick

Question 14

Wuchereria

Answer 14

Filarial nematodes - in lymphatic glands
1. Adults in lymphatic glands and release larvae
2. Move around body and larvae make way to peripheral blood system - to surface of skin at certain times of day (depends on mosquito host)
3. Blood meal taken up with larvae in - some development in mosquito
4. Makes way to proboscis and passed to next human
5. Development to adult in human
Causes elephantiasis as blocks lymph ducts

Question 15

Fatal symbiosis?

Answer 15

Most are associated with Wolbachia - so can be treated with antibiotics, as cannot live without bacteria