Phylum Arthropoda
-jointed-foot animals
Ancestral forms
- multiple segments.
repeated structures both internally/externally.
- with paired appendages.
specialisation of appendages
- anterior region - feeding apparatus, sensory.
- middle region - retained locomotory function.
- posterior region - locomotory (if present) and reproduction.
Tagmosis
- grouping of body segments.
- in insects, regions become well defined.
- three tagma: head, thorax and abdomen.
Head (6-7 segments)
externally,
appendages modified to support functions of:
- feeding, vision, taste, smell.
internally
brain - integrative centre.
Thorax (3 segments)
- legs
- wings - not derived from appendages.three segments
prothorax
mesothorax pterothorax Adult
metathorax " Adult
- internally consequence of this locomotory function - muscle.
Abdomen (11 segments)
- loss of appendages.
- formation of external portion of reproductive system.
- numerous exquisite parts - species recognition (mating)
- internally digestive, excretory, reproductive systems concentrated.
Exoskeleton
- invertebrate - no backbone.
- external skeleton.- integument (multilamellar) SKETCH
epicuticle (cement and wax) - secreted
exocuticle - secreted
endocuticle - secreted
epidermis (epithelial layer) - cellular - bipolar secretion
basal lamina (basement membrane) -secreted
Functions:
i. protection
ii. mechanical - muscle attachment
iii. prevents dessication
Hardened exterior - engineering problem. SKETCHES
solution.
main body - hardened blocks/plates divided by flexible regions.
appendages - subdivide into portions (articles) with hinges.sclerites - thickened, stiffer regions.
- blocks/plates of cuticle, functionally arranged.
- separated by membranous regions.
tergum, pleuron, sternum.
- sutures - "lines" which remain visible from the surface where fusion of plates occurred.
- pits
- apodemes, phragma
- sulcus - lines which demarcate internal projections of the exoskeleton.
Same tissue (exoskeleton) can have such differences in hardness.
- due to differential amounts of cross-linking:
key players:
- chitin - long polymers of N-acetylglucosamine.
- quinones - cross-linkers.