1. INSECT BODY PLAN
AND
EXOSKELETON

2. Arthropod Lineages

3. What about the Onychophora (“velvet worms” )?
Annelid Arthropod
Characteristics Characteristics
Peripatus
-worm-like body -segmented legs
(during embryogenesis)
-paired nephridia - open circulatory system
- hemocoel
- trachea
- oral appendages

4. Insect Body Plan
Tagmata
Head
Thorax
Abdomen
6 segments
- sensory & feeding
3 segments
- locomotion
11 segments
digestion & reproduction
Total of 20 segments (primitively)

5. Insect Body Plan Tagmata Head Thorax Abdomen Cross section
tergum (notum)
pleuron
pleuron
sternum

6. Insect Body Plan
tergum (notum)
pleuron
pleuron
sternum
Note: The bits of exoskeleton (the pieces in the puzzle) that make up the outer surface of an insect are collectively referred to as sclerites.
Each surface of an insect has its own sclerites which are referred to as tergites, sternites and pleurites.

7. 1) Primitive Condition (annelids, larval insects)
Insect Body Plan
Segments
1) Primitive Condition (annelids, larval insects)
primary segment
primary segment
primary segment
longitudinal muscle
intersegmental fold

8. 2) Intermediate Stage (hypothesized)
Insect Body Plan
Segments
2) Intermediate Stage (hypothesized)
primary segment
primary segment
primary segment
longitudinal muscle
segmental sclerite
intersegmental sclerite

9. 3) Third Stage (seen in Apterygota)
Insect Body Plan
Segments
3) Third Stage (seen in Apterygota)
secondary segment
primary segment

10. 3) Third Stage (seen in Apterygota)
Insect Body Plan
Segments
3) Third Stage (seen in Apterygota)
secondary segment
primary segment
4) Final Stage (seen in Pterygota)
phragma

11. Insect Integument (Exoskeleton)
Why are insects crunchy?
Outer epicuticle
Epicuticle
Inner epicuticle
Exocuticle
Procuticle
Endocuticle
Schmidt’s layer
Epidermis
Basement membrane
Pore canals

12. Insect Integument (Exoskeleton)
Why are insects crunchy?
Outer epicuticle
Epicuticle
Inner epicuticle
cement
wax
oriented wax
cuticulin
Inner epicuticle
Exocuticle (procuticle)
pore canal

13. Insect Integument (Exoskeleton)
cement
Insect Integument (Exoskeleton)
wax
oriented wax
Wax Layers - Control of Water Movement
WATER
WATER
WATER IS RETAINED

14. n Insect Integument (Exoskeleton) N - acetylglucosamine polymer H H H
O = C - CH2 NH H
CH2OH O O H H H H OH O H H OH O NH
CH2OH H
O = C - CH2 n

15. Insect Integument (Exoskeleton)
O = C - CH2 NH H
CH2OH O H H H H OH O H H OH O NH
CH2OH H
O = C - CH2 CO NH CO NH CO NH NH CO NH CO NH CO CO NH CO NH CO NH NH CO NH CO NH CO
hydrogen bonds

16. Insect Integument (Exoskeleton)
microfibril
N - acetylglucosamine polymer
sheets of microfibrils
orientation of microfibrils changes

17. Insect Integument (Exoskeleton)
Protein Matrix

18. Insect Integument (Exoskeleton)
Cross linking of protein matrix

19. Insect Integument (Exoskeleton)
Cross linking of protein matrix OH O OH OH O OH OH OH
Protein
Protein
CH2
CH2
Protein C
Protein
CH2
CH2
CH2
CH2
CH2
N-acetyl dopamine
N-acetyl dopamine quinone

20. Insect Integument (Exoskeleton)
kg/mm2
Tensile strength of sclerotized chitin (sclerotin)