external morphology. goal: to be able to tell insect from other animals

• bilaterally symmetrical (looks same across y axis)
• phylum arthropodia: 6 general characteristics that all share
  • bilateral symmetry
  • segmented body
  • exoskeleton
  • open circulatory system- no blood, but circulates through body unlike human which is clsoed system
  • ventral nerve cord (nervous sytem on bellies)
  • doral artery (part of circulatory system. on back)
• arthropods in comparison to mammals are upside down and inside out (see given cross section in lecture 2 slides)
  • exoskeleton vs endoskeleton - what provides support for us
• jointed exoskeleton
  • multilayered shell
  • varies dynamically like a suit of armour
  • UNLIKE suit of armor has no gaps
  • exoskeleton pros: efficient at small size, good protection for soft internal structgures. flexible for flight
  • drawbacks: growth must occur in discrete stages
  • molt to grow, but during molt extremely vulnerable to predation. does not allow for gradual growth proccess.
  • size limits factors and surface area to volume issue
    • if you get too big you are really really heavy. need to not collabse on self bc of weight, no endoskeleton. exos can become overstressed. beeds to be hard enough, but not too heavy,
• head: sensory, ingestion, brain
• thorax
  • wings go up and down: contraction and relaxation of muscles in thorax moves wings

NOT an insect

• arachnida (spiders, scorpions).
• myriapoda (milipedes, centipedes) antennae, lots of segments
• crustaceans (crabs lobsters shrimp waterfleas)
• hexapods (insects and near relatives)