Arthropods

Chapter 28

What is an Arthropod? Characteristics: Invertebrate animals

with bilateral symmetry

A coelom Exoskeleton Joint appendages

Appendages Are anything like

legs, antenna that grows out of the body

Are adapted for sensing, walking, feeding & mating

Arthropods were 1st to evolve jointed appendages

Appendages Allows for more

powerful movements Different uses ex: spiders use

their 2nd pair of appendages for sensing & mating

Ex: scorpions seize their prey

Purpose of exoskeleton Gives protection Supports internal

tissue-gives muscles place to attach

Some covers entire body-some animals held together by hinges

Made of Chitin

Disadvantages of Exoskeleton Relatively heavy

structure (Jump & Fly)

Cannot grow so they shed periodically- molting

Most molt 4-7 times during their life

Most vulnerable to predators

Steps Associated with Molting1. A new one develops beneath the old one

2. The muscles contract in the rear part of the body, forcing blood forward causing this part of the body to swell & split

3. The animal wiggles out

Spider Molting

http://www.youtube.com/watch?v=zXhdr0TpOwY

Body segments of Arthropods Segments have fused

into 1 – 3 body sections

1. Head

2. Thorax

3. Abdomen

Body segments of Arthropods Other groups have 2

body segments

1. Fused head & thorax called a cephalothorax

2. abdomen

Movement Generally quick, &

active Can crawl, run,

climb, dig, swim & fly

Flies beat their wings 1000 times/sec

3 types of Gas Exchange (Air)1. Gills

aquatic arthropods (lobster, crayfish, crab…) exchange gas through gills

3 types of Gas Exchange (Air)2. Tracheal Tubes

Most insects have tracheal tubes-branching network of hollow air passages

3 types of Gas Exchange (Air)3. Book lungs

Most spiders have book lungs – air filled chambers that contain leaf-like plates that look like pages of a book

Acute Senses Movement, sound &

chemicals are detected with an antennae

Antennae also aid in communication

Antenna Ants work together

because they communicate with a pheromone-which is a chemical odor signal given off by the animal and detected with the antenna

A Bugs Life…Wonderful Example

http://www.youtube.com/watch?v=jrW_TTxP1ow

Vision is important Most arthropods have 1

pair of large compound eyes (visual structures with many lens)

Or 3-8 simple eyes (visual structure with 1 lens)

Total images make up thousands of parts (dots like a t.v. screen)

Nervous System Well-developed that

can process information coming in from the sense organ

Most excrete waste through Malpighian Tubes

Other complex body systems

Mouth parts include a variety of jaws called mandibles adapted for holding, chewing, sucking or biting different foods

Other information1. Have separate male &

female species

2. Reproduce sexually -fertilization

occurs internally in land species

-externally in aquatic species

3. Blood is pumped by 1 or more hearts to an open circulatory system

4. Have complete circulatory system, & digestive system

Beneficial to Humans1. Pollinate many

flowering plants & crop plants

2. Provide food, honey, shellac, wax & silk

3. Provide alternative chemical control of insects

4. Research has advanced in the fields of genetics, evolution, and biochemistry

-Crab shells make artificial skin, surgical sutures & antifungal medicines

Problems for Humans1. Insects eat important

crops (bole weevil)

2. Spread plant and animal disease (malaria & yellow fever)

3. Costly for us…

Crustaceans

Crustaceans: Mostly are aquatic Have mandibles for

crushing food 2 pairs of compound 2 pairs of compound

eyeseyes which are on moveable stalks

5 pairs of walking legs used to seize prey & clean appendages

Characteristics:

The first pair of walking legs are often modified into strong claws for defense.

Shrimp

Members of Crustaceans Barnacles

Crab

A Few Land Crustacean Pill Bug & Sow Bug,

two of the few land crustaceans, must live where there is moisture, which aids in gas exchange

Pill Bug

Sow Bug

Horseshoe Crab Horseshoe crabs are

considered to be living fossils & have remained relatively unchanged since the Triassic Period

They forage on sandy or muddy ocean bottoms for algae, annelids, and mollusks

Insects: class Insecta Insects have three body

segments and six legs There are more species of

insects than all other classes of animals combined.

Only group of animal that has never lost an individual to extinction

Centipedes Centipedes are

carnivorous and eat soil arthropods, snails, slugs, and worms

The bites of some centipedes are painful to humans.

Millipedes A millipede eats mostly

plants and dead material on damp forest floors.

Millipedes do not bite, but they can spray foul-smelling fluids from their defensive stink glands.

Leaf Cutter Ants

http://www.youtube.com/watch?v=RH3KYBMpxOU

Other Members… Lice, Grasshoppers,

flies, butterflies, bees & beetles….

Insect Reproduction Most insects lay a

large number of eggs, which increase the chances that some offspring will survive long enough to reproduce.

The insect embryo develops and the eggs hatch

Metamorphosis: change in body shape and form• This series of changes, controlled by

chemical-substances in the animal

• 2 types of metamorphosis

1. Complete Metamorphosis

2. Incomplete Metamorphosis

Complete Metamorphosis Complete metamorphosis consist of four stages

on their way to adulthood:

Egg Larva Pupa Adult.

Incomplete Metamorphosis Incomplete metamorphosis consist of three

stages on their way to adulthood

Egg Nymph Adult

Arachnids

Spiders, Scorpions, Mites & Ticks

Arachnids 30,000 species of

spiders – only 12 native to North America

Cannot chew food-use digestive enzyme to liquefy food

Crab Spider

Ticks & Mites Differ from spiders

because they only have one body segment

scorpions Scorpions are easily

recognized by their body segments & enlarged pinchers

They have a long tail with a venomous stinger at the tip.

Arachnids known for webs Silk is made from silk

glands & is spun into thread by spinnerets located at the rear of the spider

Link for spider webshttp://www.i-is.com/users/robin/spiderweb.html

Spider spinning an insect

http://www.youtube.com/watch?v=_-A8Oe43tjg&NR=1

Venomous Spiders… Black Widow

web used in WWI for cross-hairs in riffles

Brown Recluse

Spiders 1st pair of appendages

called chelicera (located near mouth, modified pinchers/fangs) used to hold food

2nd pair called pedipalas handle food & sensing

Banana Spider