INSECT BODY PLAN AND EXOSKELETON

Arthropod Lineages

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

Insect Integument (Exoskeleton) Protein Matrix

Insect Integument (Exoskeleton) Cross linking of protein matrix

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

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