Ecdysozoa Flashcards
What are the five phyla included in Ecdysozoa
- Nematoda
- Nematomorpha
3.Tardigrada - Onychophora
- Arthropoda
What do all Ecdysozoans have in common
They possess a cuticle that is moulted during growth — a process called ecdysis
What are the main challenges of having a stiff cuticle
Growth (cuticle doesn’t stretch)
Locomotion (must move despite external constraint)
How was Ecdysozoa identified as a clade
Through molecular phylogeny (DNA sequences), not morphology — the name and group were proposed only after genetic evidence
What evolutionary insight does Ecdysozoa’s position in the tree give
A stiff cuticle evolved early in this lineage.
Moulting (ecdysis) enabled size increase despite cuticle rigidity
What is the structure of the nematode cuticle, and how does it function
Made of collagen, arranged helically
Provides springiness and resists deformation
Permeable to water and gases, moulted 4 times
Why cant nematodes move like annelids
They lack circular muscles and segmentation, so movement is achieved only by longitudinal muscles
How do nematodes move with only longitudinal muscles
Antagonistic contractions of left and right sides
Springiness of cuticle stores and releases energy
High-pressure body fluid helps restore body shape
What makes nematodes rigid despite no skeleton
A high-pressure pseudocoelomic fluid (10x that of most invertebrates) acts as a hydrostatic skeleton
How do nematodes keep their gut open under pressure
Muscular pharynx (triradiate) at the mouth
Anus muscles to control pressure release
What is the nematode movement pattern called
Sinuous body waves, efficient for moving through soil, fruit, or tissue = poor swimmers
What is the life cycle of Ascaris (pig/human roundworm)
Single host
Ingested from contaminated soil
Larvae migrate: intestine → liver → lungs → back to intestine
Eggs passed in faeces
What causes River Blindness and how is it transmitted
Onchocerca volvulus
Lives in lymphatic tissue under skin
Damages skin and eyes
Transmitted by blackflies in flowing water
Controlled with anti-nematode drugs
Why is Caenorhabditis elegans an important model organism
First animal with fully sequenced genome (1998)
Fixed cell lineage (eutely) known for every cell
Full neuronal wiring mapped (302 neurons)
Key in discoveries like apoptosis
Widely used in cell biology and genetics
How are nematomorphs similar to nematodes
Unsegmented
Only longitudinal muscles
Moulted cuticle
How are nematomorphs different from nematodes
Much longer
Non-functional gut in adults
Adults are free-living in water; juveniles are arthropod parasites
Describe the life cycle of nematomorphs
- Adults breed in water
- Larvae infect mayfly nymphs
- Mayflies are eaten by crickets
- Inside crickets, the worm develops
- Controls cricket behaviour to jump into water for emergence
What are key features of tardigrades
Moulted cuticle
Stumpy, non-jointed legs
Live in moss or water
Tiny but abundant
What is anhydrobiosis, and why is it important in tardigrades
A survival strategy where they enter a tun state by secreting jelly and drying out to survive harsh conditions like desiccation
Where do Onychophorans live, and how do they hunt
Rotting wood in tropical forests
Slow predators that trap prey using glue guns (sticky slime)
What are the structural traits of Onychophora
Moulted but soft cuticle
Stumpy, non-jointed legs
Share features with both arthropods and annelids
