Arthropods

What are ARTHROPODS?

• Coelomate

• Segmented

• Bilateral Symmetry

• Exoskeleton – made of protein and chitin

• Jointed appendages – any structure (leg or antennae) that grows out of the body

• earliest invertebrates to exhibit jointed appendages– Jointed appendages are an advantage

because they allow more flexibility for animals with hard, rigid exoskeletons

– Joints allow powerful movements and allow appendages to be used in many ways

What are Arthropods?

What are Arthropods?

Appendages

Jointed Appendages

• made up of protein and CHITIN

• can be a continuous

covering over most

of body OR made of plates

that are held together by hinges

Exoskeletons Provide Protection

Continuous

Hinged

• Protects, supports internal tissues

• Provides place for muscle attachment

• Aquatic arthropods have exoskeleton reinforced with calcium carbonate

Exoskeleton Advantages

Exoskeleton Disadvantages

• Heavy– the larger the animal, the thicker and

heavier the exoskeleton

• Exoskeletons don’t grow– animals must molt when they get too large

for exoskeleton

Molting• Animal contracts muscles and takes in

air or water

• Body swells and causes exoskeleton to split open, usually along the back

• Most arthropods will molt 4-7 times before becoming an adult.

• increased circulation to all parts of the body cause the animal to puff up and new exoskeleton hardens leaving some “growing room”

• animal can’t protect itself, can’t move

Before the new exoskeleton hardens...

Question 1

Which of the following organisms would be most likely to have an exoskeleton reinforced with calcium carbonate?

A. Spider

B. Beetle

C. Crab

D. Dragonfly

Correct!

Question 2

• Exoskeletons are heavy. Why can aquatic arthropods grow so much larger than terrestrial arthropods?

The buoyancy of the water helps support the weight of the exoskeleton

Question 3

• What is one advantage and one disadvantage of flying arthropods having a thinner, lighter weight exoskeleton?

Disadvantage: less protection

Advantage: greater freedom to fly and jump

Question 4

• What is one advantage and one disadvantage of having a cephalothorax?

Disadvantage: less flexibility, mobility

Advantage: more protection

Segmentation

• 3 segments – abdomen – thorax – head

• Sometimes these segments can be fused together– some have head and fused thorax and

abdomen– some have abdomen

and fused head and

thorax (cephalothorax)

Segmentation

Respiration

• Efficient respiratory systems to meet large O2 demands

• Large O2 demand needed to sustain high metabolism for fast movements

• 3 types of respiratory structures– gills (aquatic arthropods)– tracheal tubes (terrestrial arthropods)– book lungs (terrestrial arthropods)

• Gills– water moves over gills– O2 from water diffuses

into gills and into

bloodstream– CO2 from body diffuses out through gills

into surrounding water

Respiration

• Tracheal tubes– branching network of hollow air passages

that take air throughout the body

Respiration

Muscle movement brings air in/out through SPIRACLES (openings in abdomen and thorax)

• Book lungs– spiders and relatives– air filled chambers with leaf-like plates– stacked plates

are arranged

like pages

of a book

Respiration

Antennae

• Acute sensing by antennae– stalk like structure that can detect changes

in the environment• movement• sound • chemicals

Used for sound and odor communication

Eyes• Compound Eyes

– visual structure with many lenses

• Simple Eyes– visual structure with one lens for detecting

light

one pair of compound eyes and 3-8 simple eyes

Nervous System

• Double ventral nerve cord

• Anterior brain

• Several fused ganglia that control the body section they are located in

Circulatory System

• Open circulatory system– blood flows away from the heart in vessels– blood flows out of vessels into tissues– blood returns to the heart through open

spaces

Digestive System• Complete digestive system with mouth,

intestine, and anus

• Mouth has 1 pair of jaws called MANDIBLES– adapted for holding, chewing, sucking, or

biting

Reproduction – Sexual and Asexual

• Sexual reproduction– separate sexes– internal fertilization for terrestrial species– external fertilization for aquatic species

• Asexual reproduction– PARTHENOGENISIS

• a new individual develops from an unfertilized egg

• seen with ants, aphids and bees

Reproduction – Sexual and Asexual

Arachnids

• spiders (largest group), ticks, mites, and scorpions

• 2 body regions: cephalothorax and abdomen

• 6 pairs of jointed appendages – 12 total appendages!

• 1st pair - chelicerae, are near the mouth

• modified into pincers (hold food) or fangs (inject poison)

Arachnids

chelicerae

• 2nd pair – pedipalps, for handling food and sensing

Arachnids

pedipalps

• Silk, for webs, is secreted by silk glands in the abdomen

• as it is secreted, it is spun into thread by SPINNERETTES

• spiders are predatory and feed almost exclusively on other animals

Arachnids

• Ticks and mites have only 1 body section

• Head, thorax and abdomen are completely fused• Ticks feed on blood of other animals

Arachnids

• Mites feed on fungi, plants, and animals

• small – not usually visible

• can transmit diseases

Arachnids

Dust mites

• Scorpions have many abdominal body segments

• Enlarged pincers

• Long tail with

venomous stinger

at the tip

Arachnids

Crustaceans• crabs, lobster, shrimp, crayfish,

barnacles

• Only arthropods with 2 pairs of antennae

• mandibles – move

from side to side

• 2 compound

eyes

• 5 pairs of walking legs

• 1st pair are claws for defense

Crustaceans

claw legs

• Most are aquatic and use gills

• pill bugs (roly-polies) live on land, but must have moisture to aid in gas exchange

Crustaceans

Yes! This is a crustacean!

• Centipedes are carnivorous – eat soil arthropods, snails, slugs, and worms

• Bites can be painful• Millipedes – eats plants and dead

material on damp forest floors• Does not bite, but does

spray foul-smelling fluid

Centipedes and Millipedes

Horseshoe Crabs

• Class Merostomata

• “Living Fossils”- unchanged for 220 million years (Triassic period)

• Extensive exoskeleton

• Live in deep coastal waters

• forage bottoms for algae,

annelids and molluscs

Insecta

• Flies, grasshoppers, lice, butterflies, beetles

• 3 body segments

• 6 legs

• Very diverse - more insects than all other classes of animals combined

• mate once in lifetime

• internal fertilization

• some exhibit

parthenogenesis

• large number of eggs

to increase survival rate

Insecta

• insect embryos develop inside eggs, eggs hatch

• some look like miniature adults– will molt

several times until adult size

Insecta

EggsNymph

Molt

Nymph

Molt

Adult

• INCOMPLETE METAMORPHOSIS– 3 stages: egg, nymph, adult

Insecta

• Nymphs can’t reproduce

• Nymph gradually becomes an adult

• Some undergo COMPLETE METAMORPHOSIS– 4 stages: egg, larva,

pupa, adult

• Metamorphosis is controlled by chemical substances in the insect

Insecta

Egg

Larva

Pupa

Adult

Insecta

• Incomplete metamorphosis: grasshoppers and cockroaches

• Complete metamorphosis: ants, beetles, flies, wasps

Origins of Arthropods

• Successful because of

– varied life styles

– high reproductive output

– structural adaptations

– hard exoskeletons

– jointed appendages

• Hard exoskeletons fossilize – a lot is known about evolutionary history

• Evolved from ANNELIDS (segmented worms)

• Arthropods have more complex segments, more developed nervous systems

• circular muscles in annelids do not exist in arthropods

Origins of Arthropods

Question 5

Spiders are:

a. predators

b. scavengers

c. decomposers

d. parasites

Predators!

Question 6

Having 2 pairs of antennae distinguish _________ from other arthropods.

a. centipedes

b. millipedes

c. crustaceans

d. horseshoe crabs

Crustaceans!

Question 7• Why are horseshoe crabs called “living

fossils?”

They remain unchanged after 220 million years!