Lecture 12 - Nematodes Flashcards
what forms do nematodes come in?
free living and parasitic
how many species
1 million - found everywhere
size of nematodes
vary alot - largest found in placenta of sperm whale - usually parasitic are larger than free living
body form
- basic - tapered at both ends
- pseudocoelomate
how do they move
undulatory locomotion
what was very important in the success of nematodes?
cuticle made of collagen - tough and flexible - can cope with hostile conditions
how many moults do they have
4 moults over life - no more moults after adult stage but still a bit of growth cos cuticle is more flexible than arthropods
nervous system
nerve ring acts like a brain - nerve chords run down the whole body
reproduction
- dioecious
- internal fertilisation - sperm cant swim against high pressure so have walking like motion
how is their sex determined
environmentally - lots of food = grow large and female
- less food = dont grow as big and male
why was Caenorhabditis elegans good to study?
- first invertebrate to have its genome sequenced
- fixed number of cells in body with fate fixed early on - use to investigate programmed cell death
what does a gene for enhanced longevity do?
can survive longer on a restricted diet
nematode parasitism radiation
- parasitism evolved several times in nematodes
- radiation accompanied evolution of flowering plants, insects and amniotic vertebrates
who is more susceptible to nematode parasite infection
children
what do heart nematodes do?
lead to complete blockage of heart
what affect can a nematode have on some species
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)
pinworm lifecycle
- 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
what is different about a hookworm?
only affects one host - larvae enter circulatory system migrate to trachea get coughed up and swallowed entering esophagus reinfecting individual
what are the largest nematodes?
ascaroids - live in gut - sheer number can lead to blockage of gut
describe filarial nematodes
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
