Ch.18, 19 and 20

Phylum Arthropoda

Arthropoda

The most diverse and

numerous of all animal

phyla

Joint-foot

900,000 species

More beetles than all

vertebrates(species)

Evolution of Arthropods

Natural selection

Fewer body segments

Specialized

appendages

Tagmata – head ,

thorax, abdomen

Cephalothorax,

abdomen

Phylum Arthropoda

4 subphyla

Trilobita-extinct

Chelicerata-chelicerae-2 body segments – 4

pairs of walking legs

Crustacea-2 pair antennae-mandibles

Uniramia-jaws-one pair of antennae-

unbranched appendages-3 pairs

Arthropoda

Cambrian period

570 million years ago

Exoskeleton developed

Molting/hormonal control

Hydrostatic skeleton lost – replaced by open

system

Annelids-Arthropods

Shared ancestor

coelom

Segmented body

Open circulatory system

Common Characteristics

Cephalization – eyes,

fused ganglia,

antennae(fiirst to form

images)

Metemerism – somites

are very specialized

Paired jointed

appendages

Exoskelton

Complex social

structures

Protective coloration

Characteristics

Bilateral symmetry

Head, thorax, tail

Cephalothorax,

abdomen

Complete digestive

system

Respiration – body

surface, gills, tracheael

tubes or book lungs

Air enters through

spiracles

Paired excretory glands-

malpighian tubules

Nervous system

Brain

Well developed system

Compound eyes 2000

separate lenses

Color and motion

Versatile Exoskeleton

Cuticle secreted by the epidermis

Made of several layers secreted during

molting

Exocuticle first then endocuticle

Layers made of chitin

Tough resistant nitrogenous polysaccharide

Insoluble in water and weak acids

Protection, coloration, movement

To grow must shed the exoskeleton or molt

Limits body size – no giant arthropods

Segmentation

Each somite – jointed appendages

Often modified

Hollow levers that are moved by internal

muscles

Sensory hairs – modified for sensory

functions, food handling, swift walking and

swimming

Air piped directly to cells

Efficient tracheal system of air tubes

Oxygen delivered directly to tissues and cells

Makes high metabolic rate possible

Limits body size

Some use gills

Complex behavior patterns

Inate controls most activities

Some learning

Complex societies and division of labor

Metamorphosis

Larval state to adult stage

Adapted for different ecological niches

Less competition among the species

Incomplete or Complete

Reproduction

Sexes usually separate

Internal fertilization

Live, eggs, eggs inside or attached

Trilobita

Before Cambrian period

200 million years ago

Abundant during the Cambrian and

Ordovician periods

Trilobed shape of body

Bottom dwelling scavengers

Could roll like pill bugs

Chelicerata

Horseshoe crabs

Spiders

Ticks

Mites

Scorpions and sea spiders

Name for mouth parts called Chelicerae

3 classes

Merostomata

Pycnogonida

Arachnida

Horseshoe crabs

Sea spiders

Scorpions, spiders,

ticks, mites

Characteristics

6 pairs of appendages

1 pair of chelicerae – suck liquid from prey

Pedipalps

4 pairs of walking legs

No mandibles

No antennae

Subphylum Crustacea

5 classes

Lobster

Crab

Shrimp

Pill bug or sow bug - terrestrial

Named after hard outer shell

Uniramia

5 classes

Chilopoda – centipedes

Diplopoda – millipedes

Pauropoda – small soft bodied myriads

Symphyla – small centipede like animals

Insecta – grasshopper to bumble bee to beetle

200 million insects for every singe human

Evolved wings 250 million years before

reptiles