Overview of Ecdysis (Molting)

Ecdysozoa

Includes all invertebrates that molt. This is a gigantic group that contains animals from crabs to insects.

Ecdysis

• Ecdysis = "Molting"
• Hard cuticle prevents organism from growing
• Cuticle: Non-living outer layer of skin
• Entire cuticle is shed during molting
• The cuticle is sclerotized (hardened)
• Sclerites: Hardened plates
• There is an unscleritized layer of cuticle beneath the hardened outer layer
• Allows for flexibility and movement
• Typically visible in the joints

The Cuticle

• There are three layers of cuticle
• Epicuticle (outer)
• Exocuticle (middle)
• Endocuticle (inner)
• Beneath all three layer is the epidermis
• Epidermis: Living cells that secrete substances to the cuticle via small ducts

Photo by Xvazquez | CC BY

The Molting Process

1. Begins before there is external evidence of molting
2. Apolysis: epidermis separates from endocuticle
3. Inactive molting fluid is secreted over the epidermis
4. Thin protective layer forms over epidermis
5. Enzymes digest endocuticle
6. Sclerotized exocuticle is not digested
7. New undifferentiated cuticle deposited beneath protective layer
8. Absorb molting fluid
9. Epicuticle is created
10. Shed old exocuticle and epicuticle
11. This step is technically "ecdysis"
12. New cuticle expands and sclerotizes
13. Will differentiate to exocuticle and endocuticle
14. New cuticle is larger when stretched out (allows for growth)

Molting GIF

Photo by T. Nathan Mundhenk | CC BY