1. Subphylum Hexapoda
Phylum Arthropoda

2. Hexapods + Crustaceans
Note: Insects and Crustaceans make up 80% of all named species
We consider Hexapods and Crustaceans “sister taxa”
Scientists believe Hexapods arose from Crustaceans
Insects are often referred to as “terrestrial crustaceans”

3. Adaptations Adaptations of appendages:
May have pads on walking legs which may be sticky to allow insect to walk upside down, such as house flies
Hind legs of grasshoppers and crickets are adapted for jumping
Mole crickets use their first pair of legs for burrowing in the ground
Water bugs and many beetles have paddle-shaped appendages for swimming
For grasping prey, the fore legs of praying mantis are long and strong
The legs of honey bees show complex adaptations for collecting pollen

4. Walking
Insects always keep 3 out of their 6 legs on the ground at all times
Some can walk on the surface of water
Water strider has on its footpads notwetting hairs that wont break the surface film of water

5. Flying Only invertebrates that can fly
Fossil evidence suggests insect wings evolved over 400 million years ago
Wings of insects are analogous to wings of mammals – evolved separately, do not have the same structure
Most insects have 2 pairs of wings
Some, such as Diptera (true flies), have one pair of wings but will have a tiny pair of halteres (balancers) what vibrate and are responsible for equilibrium during flight
Some have one pair of wings with no halteres
Some, such as the silverfish, are wingless
Reproductive female ants shed their wings
Reproductive termites have wings, but workers are wingless
Lice and fleas are also wingless

6. Flying
Wing movements are controlled by a complex of muscles in the thorax:
Direct flight muscles- attaches to a part of the wing itself, also controls wing angle
Indirect flight muscles- not attached to wing but cause wing movement due to change of shape of the thorax
Figure 21.11

7. Vision Insects usually have 2 types of eyes
Simple eyes- 3 ocelli used to monitor light intensity and photoperiod (length of day)
Compound eyes- allows sight in almost all direction, but image may be fuzzy
Bees can detect color, but in the ultraviolet range in which humans can not see
Although flowers look one color to us, bees can see ultraviolet lines and shapes on the flower acting as a “nectar guide”
Many insects, such as butterflies, also have vision sensitive to red wavelengths, but bees are red-blind

8. Reproduction Most insects are sexually reproductive
Moths release pheromones for attract males
Fireflies use flashes of light
Some find each other but sounds or color signals or by courtship behaviors
Fertilization is internal, sperm is released directly into spermatophores
In silverfish, males deposits sperm into spermatophore and places on ground. He will then spin signal threads that will attract a female to it.
Copulation evolved later
Many insects only mate once in their lifetime
Some can go through parthenogenesis
Development of an embryo from an unfertilized egg
Or when the sperm and egg fail to unite

9. Metamorphosis
Ametabolous (Direct) Development: juveniles are similar to adults.
stages are eggs, juvenile and adult
Ex. Silverfish, spring tails

10. Metamorphosis
Hemimetabolous (incomplete) metamorphosis: gradual metamorphosis
Young are called nymphs, wings star as buds
As the animal grows and molts, the wings grow progressively larger and become winged adults
Ex. Grasshoppers, cicadas, mantids, and terrestrial bugs

11. Metamorphosis Holometabolous (complete) metamorphosis: complete change
88% of insects
Stages: egg, larva, pupa, adult
Each stage functions without competition with the other stages
Larve insects include: caterpillars, maggots, bagworms, fuzzy worms, or grubs
Pupa is the non feeding stage in which the insect is enclosed by a case
Adult insects emerges revealing an insect with wings. Within a short time, wings will expand and harden
No further molting will occur

12. Subphylum Hexapoda
Evolution

13. Classes
Class Entognatha
Class Insecta

14. Class Entognatha Small group
Mouthparts enclosed within the head capsule
3 Orders
Protura and Diplura are tiny, eyeless and inhabit soils or dark damp places where they are rarely noticed
Collembola are commonly known as springtails because of their ability to leap; an animal 4mm long may leap 20 times its body length.

15. Class Insecta Most diverse and abundant groups of arthropods
1.1 million species have been classified, but scientists believe that over 30 million species exist.

16. Characterisics Usually have 2 pairs of wings 3 tagmata:
Head
Thorax
Abdomen
Large compound eyes
Pair of antennae
Used as: tactile organs, olfactory organs and auditory organs (Touch, Smell, Hear)
3 ocelli (simple eyes)

17. Characteristics Thorax is composed of 3 parts:
Prothorax
Mesothorax
Metathorax
Each bear appendages and the mesothorax and metathorax bear a pair of wings.
Abdomen is 9-11 segments
Genetalia emerge from segments 8 and 9
Typically insects feed on plant juices and plant tissues, while some insects eat dead animals or smaller insects
Respiration by Tracheal System

18. Next Week Next class: Test – Nematodes, Annelids and Arthropods
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