Nematoda Flashcards
What are the 5 features of nematodes - round worms
Apparently they can be found anywhere that can support life !
They are not segmented
They have a ‘body cavity’ - this cavity is a pseudocoelom not coelom - it has liquid at a very high pressure
Only longitudinal and not circular muscles
Criss-cross collagen fibres in cuticle, moulting
Eutely - a fixed number of cells
Talk about their body cavity
It is a ‘body cavity’ - pseudocoelom
This means that the cavity is NOT lined by epithelial cells
Cavity is left over from blastocoel from embyro
It has liquid at very high pressure 10mm Hg
10 times that of other inverts
This is why they are round worms
These worms have a mouth and anus - through gut
What is the solution to the problem of having a through gut and very high pressure?
a) Muscles at anus control opening and closing
b) Muscular pharynx at mouth - triradiate pharynx.
Pumps at 4 pulse/second
It only has longitudinal muscle: so how does the worm work?
How can a worm work with only longitudinal muscles?
1) two ‘sides’ of the worm antagonise one another
2) the cuticle is CRUCIAL
Describe the cuticle in further detail
Draw it!!
The epidermis secretes a cuticle that is moulted 4 times before a nematode becomes an adult - the cuticle often has hairs, spines, or annulations, and may have longitudinal ridges.
The nematode cuticle has several layers
The four basic layers: externally there is a v thin trilaminar epicuticle that is 6-40nm thick. Outer surface, surface coat of glycoprotein, secreted by epidermal glands. The three underlying layers are made up of collagens stabilised by disulphide bonds.
Helical collagen fibres Compress and bend Acts to extend the muscles Permeable to water and gases Moulted 4 times
How does nematode locomotion work?
No segmentation, high pressure fluid, only longitudinal muscle, springy cuticle: all this combines:
Sinous body waves = good for through soil, fruit, or body tissues. They move by sequential contraction of longitudinal muscles, opposed the relatively flexible but inextensible cuticle. Forward or backward body waves, curling and uncurling.
but bad swimmers - not found in plankton. Would be energetically inefficient to swim because they would have to use rapid body waves.
Talk about Ascaris (intestinal roundworm)
Ascaris (in pig or human)
Single host
Infection by ingestion
Eggs passed in pig/human faeces
Eggs survive for years in the soil and are impervious to disinfectants
Juveniles migrate through lungs and liver and back to intestine
Has a characteristic sharp kink at the end of the tail
The guinea worm
Found in Africa and South Asia
Adult female is around 80cm long
Lives under human skin and forms painful ulcers
life cycle phase inside FW copepod crustacean
Human infection by drinking water with infected copepods
Describe elephantiasis
Elephantiasis (lymphatic filariaris)
Wuchereria bancrofti, Brugia malayi and Brugia timori all transmitted by mosquitoes
Nematode infects lymph glands, causing fluid build up
River blindness - onchocera volvulus
In lymphatic system, just below the skin and causing inflammation
Damages skin, eye lens, and retina
Transmitted by black flies in flowing water
Sing the praises of c. elegans
First animal to have its genome completely sequenced (1998)
• Cell lineage entirely known, fate of every single cell! (NB: eutely) = 959 in the adult hermaphrodite; 1031 in the adult male
• Connections of every single neuron mapped (302 neurons)
• A major model system in studying disease genes etc
• Programmed cell death (apoptosis) was first discovered in C. elegans
Talk about the eutely of c. elegans
During development, 1090 cells are generated, but precisely 131 of these cells are eliminated by programmed cell death. This results in an adult nematode (the hermaphrodite), composed of 959 somatic cells.
What are the similarities and differences between nematodes and nematomorpha ?
Same:
Unsegmented
Longitudinal muscles
Moulted cuticle
Differences
Really, really long
Reduced gut, no function
Not eutelic
Talk about juveniles parasite in arthropods
Grow inside insect or crustacean host,
Burst out into river or pond
If host is terrestrial, can even modify behaviour of the host!
