LECTURE 11 - Ecdysozoa: Nematoda

Question 1

What is the armour plate made of?

Answer 1

• Composites: fibres/matrix
• Skin: chitin/ECM
• Wood: cellulose/lignin
• Flesh
• Mineralized chitin
• Calcium salts: shells and tubes
• Metal: tank armour
• Stab-proof vests: aramid/thermoplastic

TOUGHNESS:
- prevent crack propogation
- Tough: resists thrusts

• Brittle, soft

HARDNESS
- prevent crack formation

• Hard: resists projectiles

Question 2

How many ways can an animal grow inside a suit of armour?

Answer 2

2

• GROW THE SUIT:
  
  • Expand an external shell to keep pace with the growing individual
  • Examples: gastropod and bivalve shells
  • Drawback: only works for simple unjointed armour that envelops the body
• THROW THE SUIT
  
  • Shed the whole of the armour at regular intervals to allow individual to get larger
  • Examples: crustaceans and insects
  • This works for complex jointed armour
  • Drawback: individual is highly vulnerable after old armour has been shed

Question 3

What are the three phyla that radiate from Ecdysozoa?

Answer 3

• Scalidophora
• Nematoidea
• Panarthropoda

Question 4

(IN SCALIDOPHORA) What is Kinorhyncha?

Answer 4

• Minute (< 1mm) marine animals, c 100 species
• Superficially segmented cuticle with spines
• Segmented muscles in body wall
• Circular muscle in head segments, longitudinal strands
• Eversible oral region (introvert) with spines
• Simple straight gut
• Capacious fluid-filled internal cavity
• ‘Cement tubes’ at posterior end of body
• Crawl slowly in muddy marine sediments using oral spines
• Feed on diatoms and detritus

Question 5

Describe the anatomy of Kinorhynch.

Answer 5

• EXTERNAL ANATOMY
  
  • Oral stylets
  • Mouth cone
  • Scalids
  • Placid
  • Sensory spot
  • Oral area: introvert, withdrawn
• INTERNAL ANATOMY
  
  • Mouth cone
  • Scalid
  • Trichosalid
  • Pharynx
  • Digestive gland
  • Midgut
  • Genital organs
  • Nephridium
  • Brain
  • Salivary gland

Question 6

(IN SCALIDOPHORA) What are Priapulida?

Answer 6

• An ancient species-poor group, 16 species
• Large: up to 10 cm length
• Benthic larva of similar form to adult
• Body wall of circular and longitudinal muscles
• Straight gut
• Large fluid-filled internal cavity
• No specialized sense organs, vascular or respiratory systems
• Nervous system of oral ring and ventral nerve cord
• Mouth armed with spines
• Circumoral region an “introvert” that can be forcibly everted
• Live buried in sediment through which they burrow
• Capture slow-moving polychaetes (annelids), etc.

Question 7

(IN SCALIDOPHORA) What are Loricifera?

Answer 7

• About 20 species
• Minute (< 1mm) marine animals
• Larva resembles adult
• Body in three regions
• Eversible oral region (introvert) with spines
• Found in marine sediments at all depths
• Strongly attached to particles with cement tubes
• Crawl using spines and mouth cone
• Pierce algal cells with oral stylets

Question 8

(IN NEMATOIDEA) What are Nematoda?

Answer 8

• Ubiquitous, abundant, diverse group of unsegmented worm-like ecdysozoans
• Ecologically important as detrivores and predators; many forms are parasitic
• About 15,000 names species, but real diversity may be much greater
• Nematode cuticle consists of a network of cross-linked collagen-like molecules
• It is shed (moulted) and re-synthesized at the end of each larval instar
• Ecdysis is accomplished by a rapid longitudinal rotation following a period of reduced activity, which tears off the old cuticle

Question 9

Describe the body plan of a Nematode.

Answer 9

• The body plan of a nematode is a tube within a tube
• Bilaterally symmetrical vermiform animals
• Body cavity is a pseudocoel containing fluid under high pressure
• There is a through-gut with a subterminal anus
• The nervous system includes a pharyngeal nerve ring
• There is no circulatory system

Question 10

What are some parasitic Rhabditids?

Answer 10

• Spirurida –> Filariasis: small nematodes infecting the subcutaneous layer of the skin, the lymphatic system or the abdominal cavity
• Strongylida –> Hookworm: nematodes live in intestine, where they may cause anaemia
• Ascaridida –> Roundworm; ascariasis: large nematodes living in the intestine of mammalian hosts
• Rhabditida –> Stronglyoidiasis: another intestinal parasite common in the humid tropics
• Oxyurida –> Pinworm: small nematodes inhabiting colon and rectum

Question 11

What family of nematodes mostly live in soil?

Answer 11

Rhabditids are mostly free-living nematodes living in soil or sediment and eating bacteria and other microbes
- Free-living nematodes are among the most improtant members of soil and sediment communities

Question 12

What are some other families radiating from Nematoda?

Answer 12

• Enoplia
  
  • Freeliving marine nematodes, including large predatory species
• Trichinellida
  
  • Obligate parasites of vertebrates; cause trichinellosis in humans
• Monochida
  
  • Freeliving soil and freshwater nematodes, preying on small animals
• Mermithida
  
  • Internal parasites of insects
• Dorylaimida
  
  • Nematodes with a movable tusk extending from the oesophagus; consume plants, algae or other nematodes

Question 13

What is the largest nematode?

Answer 13

• Placentonema is the largest nematode
  
  • Specimens up to 8m in length have been recovered from the placenta of sperm whales

Question 14

(IN NEMATOIDEA) What are Nematomorpha?

Answer 14

• Worm-like ecdysozoans have unsegmented exoskeletons called cuticles
  
  • The horsehair worms (phylum Nematomorpha) consist of about 320 species
    
    • They are pseudocoelates
  • They are extremely thin and range in length from a few mm to 1m
  • Most adults live among litter and algal mats near the edges of streams and ponds
  • The larvae are internal parasites of terrestrial and aquatic insects and crabs
  • The gut is much reduced with no mouth opening and is mot likely non-functional
  • They may feed only as larvae, absorbing nutrients from their hosts across their body wall