Lecture 12 - Nematodes

Question 1

what forms do nematodes come in?

Answer 1

free living and parasitic

Question 2

how many species

Answer 2

1 million - found everywhere

Question 3

size of nematodes

Answer 3

vary alot - largest found in placenta of sperm whale - usually parasitic are larger than free living

Question 4

body form

Answer 4

• basic - tapered at both ends

- pseudocoelomate

Question 5

how do they move

Answer 5

undulatory locomotion

Question 6

what was very important in the success of nematodes?

Answer 6

cuticle made of collagen - tough and flexible - can cope with hostile conditions

Question 7

how many moults do they have

Answer 7

4 moults over life - no more moults after adult stage but still a bit of growth cos cuticle is more flexible than arthropods

Question 8

nervous system

Answer 8

nerve ring acts like a brain - nerve chords run down the whole body

Question 9

reproduction

Answer 9

• dioecious

- internal fertilisation - sperm cant swim against high pressure so have walking like motion

Question 10

how is their sex determined

Answer 10

environmentally - lots of food = grow large and female

- less food = dont grow as big and male

Question 11

why was Caenorhabditis elegans good to study?

Answer 11

• first invertebrate to have its genome sequenced

- fixed number of cells in body with fate fixed early on - use to investigate programmed cell death

Question 12

what does a gene for enhanced longevity do?

Answer 12

can survive longer on a restricted diet

Question 13

nematode parasitism radiation

Answer 13

• parasitism evolved several times in nematodes

- radiation accompanied evolution of flowering plants, insects and amniotic vertebrates

Question 14

who is more susceptible to nematode parasite infection

Answer 14

children

Question 15

what do heart nematodes do?

Answer 15

lead to complete blockage of heart

Question 16

what affect can a nematode have on some species

Answer 16

can manipulate the behaviour of some animals e.g. shrimp are intermediate host and they can make them swim to surface of the water so they are eaten by a bird (final host)

Question 17

pinworm lifecycle

Answer 17

• zygotes released from host onto bedclothes and into airbourn dust
• eggs mature and enter new host by ingestion
• eggs hatch in intestine
• larvae mature in gut and migrate to anal region

Question 18

what is different about a hookworm?

Answer 18

only affects one host - larvae enter circulatory system migrate to trachea get coughed up and swallowed entering esophagus reinfecting individual

Question 19

what are the largest nematodes?

Answer 19

ascaroids - live in gut - sheer number can lead to blockage of gut

Question 20

describe filarial nematodes

Answer 20

block lymph ducts causing fluid filled tissue (elephatiasis)

• intermediate host = mosquitoe larvae
• symbiotic relationship with wolbachia bacteria - can be treated by antibacterial agent which kills nematode and bacteria