Class notes
Arthropods III and IV
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Lecture notes on arthropods (part of Bilaterians, Molluscs, and Arthropods)
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Arthropods IIIHexapods - 6 thoracic legs
They have 3 pairs of legs. All insects are hexapods but not all hexapods are insects.
3 tagmata (abdomen, thorax, head)
Most adults have 2 pairs f wings
1 pair of antenna
Compound eyes
Tracheal system for respiration
Sub phylum hexapods aren't quite insects. There are 2 roups within hexapods: insects and
entognatha.
Entognatha have retracted mouthparts, many are blind, wingless. (example is springtails)
Hexapod respiration
Respire through trachea
Branched airways
Allowe insects to colonise land
Body movement forces CO2 out
Has spiracles
Respiration through trachea limits body size because oxygen transport is less efficient as the body
size increases. 300mya the atmosphere level of O2 was 35% so dragonflies were a lot bigger.
Insects are ecologically important
Recycle nutrients, break down dead material
Plant pollinators and seed dispersal
Maintain plant community composition through grazing
Food for animals
Animal parasites
Insects have a variable diet.
They’ve evolved to fit many niches
Efficient digestion relies on efficient excretion
Efficient digestion must minimise water loss
Efficient digestion may involve endosymbionts
Phloem feeders - too much water and sugar so they have malpgian tubules that remove water and
sugars
Desert insects don't get enough water so the malphigian tubules are tightly bound to rectum to
extract as much water as possible.
Evolution of flight
Origin of flight (allows insects to find new niches to adapt to) theory that wings came from
gills (locomotion and swimming) also another theory that wings evolved from lobes on
thorax
Direct flight muscles (dragonflies and cockroaches) - directly attached to wings
Indirect flight muscles (most other insects) - muscles attached to thorax and the wings are pivoted.
Hexapods during development
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