Lecture 20: Ecdysozoa

Question 1

What is Ecdysis?

Answer 1

• the process of melting the cuticle in order to grow

* the entire cuticle (which is the non living part of the animal) sheds at once

Question 2

what is the cuticle made of?

Answer 2

• made of chitin
• frequently sclerotized (hardened)
• unsclerotized cuticle in b/w are flexible and allows for movement

Question 3

What is in the cuticle?

Answer 3

• Epidermis: living cells that secrete substances to form cuticle
• it has 3 layers
• endocuticle (inside)
• exocuticle (outside)
• epicuticle (on top)

Question 4

in the moulting process, how does it start?

Answer 4

• with Apolysis which is where the epidermis separates from the old endocuticle
• the endocuticle is digested
• liquified products are taken up by the epidermis
• sclerotized exocuticle is not digested
• new cuticle is “wrinkled” therefore greater surface area than old one
• the moulting fluid is reabsorbed
• the epicuticle (wax layer) laid down
• shed old exocuticle and epicuticle (ecdysis)
• new cuticle is expanded

Question 5

what is another phylum that experiences ecdysis?

Answer 5

Nematodes

Question 6

What is there to know about the phylum nematodes?

Answer 6

• round worms and thread worms
• they are morphologically similar to ecdysozoa
• no segmentation
• no appendages
• no eyes
  slightly blunt at one end and pointy on the other
• like other Ecdysozoa, they must moult non living cuticle

Question 7

more characteristics about nematodes…

Answer 7

• complete digestive system
• no circulatory system
• have a hemocel (fluid filled body cavity)
• direct development
• Eutelic: post embryonic growth occurs by each cell growing, not by addition of cells
• they rely on the hemocel which acts as a hydrostatic skeleton for movement
• most are free living (soil, fresh water, marine)
• many parasitic species
• medically important