The Ecdysozoa Flashcards
The Ecydysozoa are nested within the
Bilateria
Give the Ecdysozoan Classes
- Nematodes
- Nematomorphs
- Tardigrades
- Onychophora
- Arthropods
- Priapulids,
- Kinorhynchs
- Loriciferans
Which are the ‘wormy’ Ecdysozoan Classes
- Nematodes
- Nematomorphs
What are the ‘leggy’ Ecdysozoan Classes
- Tardigrades
- Onychophora
- Arthropods
What do the Ecdysozoa have in common?
cuticle moulted as animal grows
Describe the Ecdysozoa
- stiff (rigid or bendy) cuticle evolved early on this branch
- moulting allows growth despite cuticle that can’t stretch much
Describe the evolutionary constraints of a stiff cuticle
problems for locomotion
Describe the Nematoda
- roundworms
- stiff cuticle: not stretchy
- cuticle, epidermis, body-wall muscles, pharynx muscles, ventral nerve cord, lateral cord, gonodcuct, oocyte,
- no segmentation
- coelom with very high liquid pressure
- helical collagen fibres in cuticle
- can’t expand/contract body regions
- characteristic thrashing motion
- e.g. “Vinegar eels”- coelom with very high liquid pressure
- helical collagen fibres in cuticle
Describe Vinegar eels
- Turbatrix aceti
- live in vinegar, gone-off cider etc
Explain the thrashing motion of nematodes
- only L, not C muscle
- stiffness allows both sides to antagonise one another
- coelom forms semi-rigid, liquid skeleton
- gives ‘round’ shape
How do Nematoda manage their through-gut?
- muscles at anus control open/close
- muscular, triradiate pharynx (sometimes called stoma) at mouth
- pumps food in, up to 4 pulse/second
Give an example of the Nematoda
- Enoplus
- 3 teeth
- 6 inner labia papillae
- 10 cephalic setae
- viewed under SEM
Describe Nematoda springiness
- specialised cuticle
- several layers
- helical collagen fibres compress and bend: extend the muscles
- permeable to water and gases
- moulted x4
Describe the Nematode specialised cuticle from top to bottom
- 3 fibrous layers
- basal lamina
- epidermis
Summarise Nematoda locomotion
- sinous body waves
- good through soil, fruit or body tissues
- bad swimmers
Give an example of Nematode ecology
parasitism
Describe Ascaris suum and lumbricoides
- intestinal roundworm
- in pig or human respectively
- single host
- infection by ingestion of eggs in soil
- eggs passed in pig/human faeces
- juveniles migrate through liver and lungs back to intestine
Describe Onchocerca volvulus
- 2-host life cycle
- in lymphatic system
- causes inflammation
- damages skin, eye lens and retina
- causes river blindness
- transmitted by blackflies in flowing water
What are some ways in which humans use nematodes?
- pesticides
- modelling (Caenorhabditis elegans)
Describe Phasmarhabditis hermaphrodita
- used as a pesticide (slug control)
- no risk of bioaccumulation and secondary poisoning
Describe C. elegans
- first animal to have its genome completely sequenced (1998)
- eutelic
- genes 959 in the adult hermaphrodite; 1031 in the adult male
- connections of every neuron mapped (302 neurons)
- model system in cell biology and disease genetics
- apoptosis discovery
eutely
cell lineage and fate of every cell known
Describe Nematoda in soil
- ~ 300 million tonnes of nematodes in top soil layers of earth
- ~ 600 million tonnes of humans on the planet
Describe the Nematomorphs
- horsehair worms
- probably sister phylum to Nematodes
- unsegmented
- only longitudinal muscles
- moulted cuticle
- very long
- reduced, non-functional gut
- e.g. Gordius robustus
Describe the life history of the Nematomorphs
- adults free-living in water (don’t feed)
- juveniles parasitic in arthropods
Give an example of a Nematomorphic life style
- free-living adults breed in water
- nematomorph larva forms cyst inside mayfly nymph
- mayfly hatches (with parasite inside)
- cricket eats mayfly where larva develops
- cricket wanders erratically back to water via nematomorph-mediated neuromodulation
Describe the Tardigrada
- cuticle, moulted
- stumpy non-jointed legs
- live in moss/water
- abundant
- tiny
- anhydrobiotic
