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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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exoskeleton
Exoskeleton
  • Major synapomorphy for Arthropoda
cuticle skeletal structure composed of chitin and protein comprising several differentiated layers
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
slide4

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

slide5

Cuticle = Epicuticle + Procuticle

Procuticle = Exocuticle (thin) + Endocuticle (thick)

slide6

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
slide7

Procuticle

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

Chitin

slide9

Sclerotization:

  • Irreversible process that darkens exocuticle
  • Results in proteins becoming water-insoluble
  • Linkage of protein chain by phenolic bridges
  • Controlled dehydration of chains
slide10

Epidermis

  • Single-celled layer
  • Produce cuticle
  • Produce wax, chemical, cement, pheromone via pore canal, wax canal, dermal gland
slide12

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.
slide13

Segmentation and tagmosis

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3

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  • 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
slide14

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
slide16

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)