Phylum ArthropodaTextbook pgs. 335-342

Spiny-backed orb weaver

Arthropod Classes• Crustaceans• Insects• Centipedes• Millipedes• Arachnids• Trilobites

(extinct)

Body Characteristics• Body Symmetry: Bilateral symmetry• Cell Organization: Cells to tissues to organs to

organ systems• Reproduction: Sexual• Body development: Most arthropods go through

METAMORPHOSIS

Just the facts…Just the facts…1. Fully developed to life

on land2. No need of a moist

environment3. Only invertebrates to

fly.4. Live in salt and fresh

water, soil, land, air5. Size ranges from tiny

mites to over 3 feet.6. Largest phylum in the

animal kingdom.

Characteristics of Arthropods• Invertebrate

• External skeleton-Exoskeleton

• Segmented body• Jointed attachments called

appendages– Wings, mouthparts, antennae,

legs

• Open circulatory system• Internal fertilization

– most reproduce sexually– They are EITHER male or

female

An Arthropod Exoskeleton• Waterproof shell– Used for protection– Helps prevent

evaporation, keeps them from drying out

– Place for muscle attachment

• Made out of chitin• As the arthropod grows

larger, it can’t expand, so it must shed its exoskeleton– Process called molting Pillbug molting its exoskeleton

Molting

The difference between a soft-shelled crab and a hard-shelled crab

Adult cockroach

A horse-shoe crab.

CRUSTACEANS•CEPHLATHORAX

and ABDOMEN•(2 BODY PARTS)

•GILLS FOR BREATHING

•HARD OUTER SHELL

Fiddler Crab

Crustacean Body Segments

• Head and thorax combined– Cephlathorax

• Then an abdomen

ARACHNIDS• Head and

Abdomen– Four pairs of legs

• Breathe with organs called book lungs

• SOME BUT NOT ALL BUILD WEBS

Tarantula Scorpion

TickBlack Widow

CENTIPEDES• 2 body sections–Head with antennae– Long segmented

abdomen

• 100 LEGGER• ONE PAIR OF

LEGS PER SEGMENT

• LONG, FLAT BODIES

• CARNIVORES

MILLIPEDES• 2 body sections–Head with

antennae– Abdomen with at

least 80 segments• “1000 Legger”• Most of the body

segments bear two pairs of legs.

• Rounder bodies• Feed on decaying

vegetable matter and are herbivores

Will curl up to avoid predators.

Insects

• The Importance of Insects:• Pollination of flowers• Destroy harmful pests• Make silk fibers–Larva of the silkworm moth

• Make food products–Bees make honey

Insect Impact on Humans

• Damage to major crops

• Can carry diseases – Ex. – some

mosquito species cause malaria

Mosquito on Human Skin

Why Insects are So Successful

• Reproduce very quickly (short generation time)

• Females produce many young

• Ability to eat a variety of foods

Why Insects are So Successful• Different species

have become adapted to live in almost ANY environment

• Ability to fly (can travel for food and mates)

Mosquito in Flight

Insect Body Structure• Insects have:

Three body parts• HEAD, THORAX, ABDOMEN

3 pairs of legs attached to the thorax

1 pair of antennae attached to the head

Insect Body Structure

Simple and compound eyes

Most insects have one or two pairs of wings attached at the thorax

Many have tubes (spiracles) which allow oxygen to travel directly to the insect’s body cells

Insect Metamorphosis• Gradual

Metamorphosis: the egg hatches into a young insect that looks like the adult, only smaller– Ex. Grasshoppers,

termites cockroaches and dragonflies

• 3 stages – • 1.The egg • 2. hatches into a nymph• 3. the nymph molts

several times growing into a larger nymph

• 4. eventually becoming the adult.

Insect Metamorphosis cont’d• Complete

Metamorphosis: the young insect looks very different from the adult form– Ex. Butterflies,

beetles, houseflies, and ants

• 4 stages – 1. The egg hatches into

a2. larva, 3. the larva forms pupa,

and 4. the pupa turns into

an adult.

Insect Examples

Black Blister Beetle

Thistle Caterpillar

17-year Cicada

Insect Examples

Weaver Ants

Robber Fly Catching a Bee for DinnerTropical

Cockroach

Moss Mantid

TRILOBITES• ONCE THE

LARGEST GROUP OF ARTHROPODS

• EXTINCT.

Comparison of the largest Arthropod Groups

Characteristic Crustaceans Arachnids Insects

# of Body Sections

2 or 3 2 3

# of legs 5 or more pairs

4 pairs 3 pairs

# of antennae 2 pairs 0 1 pair

Where found Water or damp places

Mostly on land

Mostly on land

Example Lobster Tarantula Praying mantis

Arthropod Review