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molt: shed entire cuticle (non-living outer layer), new cuticle is grown under old one
- epidermis is below cuticle
- frequently sclerotized (hardened)
- below cuticle
- living cells that secrete substances to the cuticle
3 layers of the cuticle?
- endocuticle (bottom layer)
- epicuticle (top layer)
hardened body parts shaped like plates
Molting steps (10)
- 1. epidermis separates from endocuticle
- 2. inactive molting fluid released by epidermis
- 3. thin protective layer deposited over epidermis, under molting fluid
- 4. enzymes in moulting fluid digest endocuticle, absorbed by epidermis
- 5. undifferentiated cuticle deposited under protective layer
- 6. moulting fluid reabsorbed
- 7. epicuticle laid down
- 8. old exo and epi cuticle shed through ecdysis
- 9. new cuticle expanded by swallowing air
- 10. new cuticle hardened
Phylum Tardigrada "water bears"
- mostly freshwater, moss and soil
- no anntenae
- whole body acts as gill
- withstand desication
Phylum Nematoda (roundworms and threadworms)
- no segmentation, appendages, or eyes
- internal fertilization, some hermaphrodites
- direct development
Cause of Nematoda's simplicity?
secondary simplification from complex body design
have a body cavity but it is not completely lined by mesoderm
Post embryonic growth is done through existing cell growth, not by addition of new cells
- Habitat/role: aquatic, predators, microbivores, decomposition, nutrient cycling
- Many parasitic
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