Insect Diversity• Subphylum Uniramia is an enormous group of mostly

terrestrial arthropods that have chewing mouthparts called mandibles (jaws).

• Uniramians consist of three classes: Insecta (insects), Diplopoda (millipedes), and Chilopoda (centipedes).

• Insects are the largest group of organisms on Earth, with more than 700,000 named species.

Orders of InsectsOrder Examples Number of species

Coleoptera“shield winged”

Beetles, Weevils 350,000

Diptera“two winged”

Flies,Mosquitoes 120,000

Lepidoptera“scale winged”

Butterflies,Moths 120,000

Hymenoptera“membrane winged”

Ants,Wasps,Bees

100,000

Insects• Insects are primarily a terrestrial group, and aquatic

insects probably had terrestrial ancestors.• Although the great majority of insects are small, others

are much larger.• Generally, the larger insects live in tropical areas.• Despite great variation in their size, all insects share the

same general body plan, made up of three body sections.

Insect Body Plan• Head

– Located on an insect’s head are mandibles, specialized mouthparts, and one pair of antennae.

– The mandibles and mouthparts of different insect species are adapted for eating different foods.

– An insect’s head usually has a relatively large pair of compound eyes and a pair of antennae.

– Like the mouthparts, antennae vary greatly in size and shape.

Insect Body Plan• Thorax

– The thorax is composed of three fused segments.– Attached to the thorax are three pairs of jointed

walking legs.– Some insects, such

as fleas, lice, and silverfish, lack wings, but other adult insets have one or two pairs attached to the thorax.

Insect Body Plan• Abdomen

– The abdomen is composed of 9 to 11 segments.– In adult insects, there are no wings or legs attached

to the abdomen.

Insect Life Cycle• The life cycles of most insects are complex, and

often several molts are required before the adult stage is reached.

• During the last molt, the young insect undergoes a dramatic physical change called metamorphosis.

Complete Metamorphosis

• Almost all insect species undergo “complete” metamorphosis.

• The wingless, wormlike larva encloses itself within a protective capsule called a chrysalis.

• Here, it passes through a pupa stage, in which it changes into an adult.

Incomplete Metamorphosis• A smaller member of species develop into adults in a

much less dramatic incomplete metamorphosis.• In these species, the egg hatches into a juvenile,

or nymph, that looks like a small, wingless adult.

• After several molts, the nymph develops into an adult.

Flight• Insects were the first

animals to have wings.• For more than 100 million

years, until flying reptiles appeared, insects were the only flying organisms.

• Flying insects were able to reach previously inaccessible food sources and to escape quickly from danger.

Basic motion of the insect wing in insect with an indirect flight mechanism scheme of dorsoventral cut through a thorax segment witha wingsb jointsc dorsoventral musclesd longitudinal muscles

Flight• An insect’s wings develop from saclike outgrowths

of the body wall of the thorax.• The wings of adult insects are composed entirely of

chitin, strengthened by a network of tubes called veins (which carry air and a bloodlike substance).

• In most insects, the power stroke of the wing during flight is downward, and it is produced by strong flight muscles.

• When at rest, most insects fold their wings over their abdomen, but a few insects are unable to do this.

• Most insects have two pairs of wings.• A few groups of insects, such as fleas and lice,

are wingless.

Flight• In most insects only one

pair of wings is functional for flight.

• In some species, the second pair of wings serves another purpose.– In grasshoppers and beetles,

the forewings act as protective wing covers.

– In flies, the hindwings are modified into knoblike structures that help control stability during flight.

Social Insects• Two orders of insects, Hymenoptera (ants, bees, and wasps)

and Isoptera (termites), have elaborate social systems.• These insects often live in highly organized societies of

genetically related individuals.• Within these insect societies,

there is a marked division of labor, with different kinds of individuals performing specific functions.

• The role played by an individual in a colony is called its caste.– Caste is determined by a combination of heredity, diet (especially as a

larva), hormones, and pheromones (chemical substances used for communication).

Insect Relatives• Centipedes and Millipedes

have similar bodies.• Each has a head region followed

by numerous similar segments.• Each segment bears one or two

pairs of legs.• Centipedes have one pair of legs

per segment and can have up to 173 segments.

• Modern millipede segments have two pairs of legs.

• While centipedes are carnivores, most millipedes are herbivores.

Comparison of Crustaceans and Insects

Characteristic Crustaceans Insects

Nature of Appendages Most are branched at the end Unbranched at the end

Antennae Two pairs One pair

Chewing Appendages Usually three pairs One pair

Location of Appendages Cephalothorax and Abdomen Head and Thorax

Respiration Gills Tracheal System

Subphylum Trilobitomorpha

• Lived from 600 MYA to 345 MYA• Dominant life form while they lived• Fed on annelids, molluscs, and

detritis (decaying organic matter)• Body flat and divided into three

segments:– Head, thorax, and pygidium

• Could roll into a ball for protection (kind of like an arthropod of today)

• Branched appendages possibly used for walking, digging, or swimming

NB #111

Subphylum Crustacea

• Includes crayfish, shrimp, lobsters, and crabs

• All aquatic….– Except some isopods and crabs

• Differences from other arthropods..– 2 pairs of antennae (other

arthropods have 1)– Biramous appendages

• Segments with two rami (structure that gives appendage a Y shape)

Subphylum CrustaceaClass Malacostraca

• Largest class of crustaceans

• Crabs, lobsters, crayfish, shrimp, mysids, shrimplike krill, isopods, and amphipods

Subphylum CrustaceaClass Malacostraca

• Crayfish:– General crustacean

characteristics– Two body regions:

• Cephalothorax– Fused head and thorax

• Abdomen– Posterior– Locomotor and visceral

functions– Form of a muscular tail

Subphylum CrustaceaClass Malacostraca

• Crayfish:– Paired appendages present in both

body regions• Two pairs of antennae• 3rd-5th pairs associated with the mouth

– 3rd pair modified into mandible» Chews and grinds food

– 4th & 5th pairs called maxillae» Food handling

• 6th – 8th- maxillipeds- handle food• 9th-13th- pereopods- walking legs

– 1st pereopod is a cheliped (large pincher)

Subphylum CrustaceaClass Malacostraca

• Crayfish:– Diet- other invertebrates, plant

matter, and dead or dying organisms

– Large stomach specialized for grinding (foregut)

– Digestive gland secretes digestive enzymes to break down food

– Gills- located in chambers– Sensory structures:

• Compound eyes, simple eyes, statocysts, chemoreceptors, proprioceptors, and tactile setae

Subphylum CrustaceaClass Malacostraca

• Crayfish:– Excretion:

• Green glands or antennal glands (actually green in color)

– Reproduction:• Dioecious• Mate after female has molted• Male flips the female on her

back• Fertilzation occurs after

copulation– Sperm deposited on female

• Eggs are sticky and secure to the female’s pleopods

Subphylum CrustaceaClass Branchiopoda

• Primarily live in freshwater

• Fairy shrimp and brine shrimp

• Flattened, leaflike appendages used in…– Respiration– Filter feeding– Locomotion

Subphylum CrustaceaClass Maxillopoda

• Short bodies and a unique combination of 5 head, 6 thoracic, and 4 abdominal segments, plus a telson

• Copepods- abundant (vector for Guinea worm)

• Barnacles- sessile & may colonize on ships

• Mostly marine

Copepod

Barnacles

Subphylum Chelicerata

• Spiders, mites, ticks, horseshoe crabs, and sea spiders

• Two tagmata– Prosoma (cephalothorax)

• Sensory• Feeding• Locomotion

– Opisthosoma• Digestion• Reproduction• Excretion• Respiratory organs