INSECT BODY PLAN AND EXOSKELETON

PHYLOGENY Myriapoda Chelicerata Hexapoda Crustacea (crabs, lobsters, barnacles) Pauropoda Diplopoda (millipedes) Chilopoda (centipedes) Arachnida (spiders, mites, ticks) Eurypterida (sea scorpions) Xiphosura (horseshoe crabs) Pycnogonida (sea spiders) Trilobita (trilobites) Symphyla Mandibulata Arthropoda ?

Arthropod Lineages

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

Insect Body Plan Tagmata HeadThoraxAbdomen Cross section pleuron tergum (notum) sternum

Insect Body Plan pleuron tergum (notum) 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.

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

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

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

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

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

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

Structure of Chitin - Albert Hoffman (1906 – 2008)

Insect Integument (Exoskeleton) NH O = C - CH 2 CH 2 OH O NH O = C - CH 2 O N - acetylglucosamine polymer O HH H OH H H O CH 2 OH H H OH H n

Insect Integument (Exoskeleton) CO NHCO NHCO NHCO NHCO NHCO NH CO NHCO NH CO NHCO NHCO NHCO NH hydrogen bonds NH O = C - CH 2 CH 2 OH O NH O = C - CH 2 O HH H OH H H O CH 2 OH H H OH H

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

Insect Integument (Exoskeleton) Protein Matrix

Insect Integument (Exoskeleton) Cross linking of protein matrix

Insect Integument (Exoskeleton) OH Cross linking of protein matrix OH C CH 2 Protein OH CH 2 O O OH CH 2 Protein N-acetyl dopamineN-acetyl dopamine quinone

What other common material has cross-linked fibres in a matrix? Plywood Oriented Strand Board (OSB) Plywood

Insect Integument (Exoskeleton) Tensile strength of sclerotized chitin (sclerotin) kg/mm 2

Some days you’re the bug, some days you’re the windshield. - Mark Knopfler