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External Anatomy I Lecture 10

External Anatomy I Lecture 10. Exoskeleton. Major synapomorphy for Arthropoda. Cuticle : skeletal structure composed of chitin and protein comprising several differentiated layers. Exoskeleton – external protection and support Apodemes – internal support and muscle attachment

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External Anatomy I Lecture 10

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  1. External Anatomy ILecture 10

  2. Exoskeleton • Major synapomorphy for Arthropoda

  3. Cuticle: skeletal structure composed of chitin and protein comprising several differentiated layers • Exoskeleton – external protection and support • Apodemes – internal support and muscle attachment • Cuticle lines tracheal tubes, foregut and hindgut • Flexible to rigid • Prevent water loss

  4. OUTSIDE • Three principal layers: • Basement membrane (inside, acellular layer) • Epidermis (cellular layer) – secrets cuticle • Cuticle (outside, acellular layer, secreted by the cells of epidermis) Epidermis + Cuticle = Integument INSIDE

  5. Cuticle = Epicuticle + Procuticle Procuticle = Exocuticle (thin) + Endocuticle (thick)

  6. Epicuticle • Three layers: inner epicuticle, outer epicuticle, superficial layer • Prevent dehydration • Wax layer important for predator deterrence, color pattern, reflect solar radiation, olfactory signal • Inextensible and unsupportive

  7. Procuticle • Chitin complexed with protein • Provide support • Many kinds of cuticular proteins Chitin

  8. Cuticle deposition from epidermis has a characteristic pattern

  9. Sclerotization: • Irreversible process that darkens exocuticle • Results in proteins becoming water-insoluble • Linkage of protein chain by phenolic bridges • Controlled dehydration of chains

  10. Epidermis • Single-celled layer • Produce cuticle • Produce wax, chemical, cement, pheromone via pore canal, wax canal, dermal gland

  11. Cuticular extensions (multicellular) Spine Setae

  12. Cuticular extensions (unicellular) Acanthae • Found in ovipositor of Hymenoptera, foregut of many insect groups, adhesive pads of Diptera Microtrichia • Part of structural coloration of many insects, taenidia of trachea, etc.

  13. Segmentation and tagmosis 6 3 11 • Insect body is divided into a series of segments, the metameres, which are grouped into three distinct regions or tagmata: head, thorax, and abdomen. • Tagmosis: amalgamation of segments into functional units

  14. Primary vs. Secondary Segmentation • Primary segmentation: • Found in nonarthropodprotostome such as Annelida • Externally visible grooves in the body wall serve as muscle attachment • Secondary segmentation: • Found in arthropods • Externally visible segmentation does not conform to internal muscle attachment

  15. Major body axis

  16. Sclerite: a plate on the body wall surrounded by membrane or sutures Tergum: dorsal plate, tergite Sternum: ventral plate, sternite Pleuron: side plate, pleurite (membrane in abdomen, sclerotized in thorax)

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