Subphylum Hexapoda Phylum Arthropoda

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”

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

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

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

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

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

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

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

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

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

Subphylum Hexapoda Evolution

Classes Class Entognatha Class Insecta

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.

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.

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)

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

Next Week Next class: Test – Nematodes, Annelids and Arthropods Notebook check Need questions and summaries for all notes Please highlight