Biologi - Animalia - Arthropoda

Arthropods

Defining Characteristics

• Segmented body plan

• Paired, jointed appendages

• Exoskeleton/molting

• Invertebrate

• Bilateral symmetry

• Most arthropods have three body segments:

– Head

– Thorax

– Abdomen

• Legs/wings extend from thorax

• Abdomen: digestion & respiration

• Some (crustaceans, arachnids) have two segments:

– Cephalothorax

– Abdomen

• Cephalothorax: fusion of head and thorax

Head Characteristics

• Compound Eye:

• Simple eyes:

• Antennae

• Mouthparts

1. Compound Eye in Arthropods

1 pair

Many lenses

Color detection.

2. Simple eyes :

Three – eight eyes

One lens

Used for light detection

3. Antennae

• Sense pheromones (scent trails, mating)

• Sense movement and sound

4. Mandibles

Jaws = menjepit

Used for chewing

Side to side movement

5. Appendage

Anything which grows from the main body of an animal

– Limbs

– Antennae

– Wings

– Fins

Name the appendages and their function

Exo-skeleton

• Hard, thick outer covering

• Allows movement

• Waxy covering on some prevents water loss

Molting: shedding of exoskeleton

• Exoskeleton doesn’t grow

• Must be replaced several times

• How molting works:

– Animal contracts muscles

– Forces blood forward

– Body swells

– Old exoskeleton splits

– Animal climbs out

– Animal swallows air

– Body swells

– New exoskeleton hardens

Arthropod Digestion

• One way digestive system

• Most have mandibles (jaws) for chewing

Types of Arthropods

• Arachnids – spiders, scorpions, mites and ticks

• Crustaceans – shellfish (crabs, lobster)

• Horseshoe crabs

• Chilopoda – centipedes

• Diploda – millipedes

• Insecta - insects

A. Characteristics of Spiders

* Two body regions:

• Cephalothorax

• Abdomen

* Simple eyes (6-8) but no compound eyes

* Spiders - Appendages

Six pairs jointed appendages

• 1st: chelicerae - pinchers/fangs

• 2nd: pedipalps – hold/capture food

• 3rd – 6th: legs - mobility

1. Chelicerae

- First pair of appendages

- End in fangs

2. Pedipals

- Capture and hold prey

- Carry sperm in males

* How Spiders Eat

• No mandibles (no chewing)

• Hold prey and injects venom

• Venom digests prey outside body

• Spider sucks prey in like a milkshake

à Hunting Strategies:

v Camouflage and ambush

v Trapdoor Spiders

v Web Spiders

v Funnel Web

* Four pair legs (insects have three)

* Web Design

• Silk secreted by silk glands

• Spinnerets spin silk into web

* Mating

• The male initiates by:

– presenting a gift

– stroking the female

– doing some type of dance

• Female usually larger

• After mating, the male dies or is eaten by the female

• Female lays eggs, and spins an egg sac to protect them (Wanita bertelur, dan berputar sebuah kantung telur untuk melindungi mereka

* Egg Sacs

• Spiders spin egg sac from silk

• Eggs remain in sac until hatching

* Dangerous North American Spiders

B. Horseshoe Crab

• Four pair walking legs

• Pedipalps

• Chelicerae

* Three kinds of Insect Development

1. Gradual Development

• Eggs hatch with babies looking just like adults.

• Molt as they grow.

• Some of the wingless insects (springtail/silverfish):

2. Incomplete Metamorphosis
Three stages:

• Egg

• Nymph:

– looks similar to adult but may lack appendages/can’t reproduce

– with each molt, looks more like adult form

• Adult

– Cockroaches

– Grasshoppers

– Cinch bugs

Grasshopper Development

3. Complete Metamorphosis
Four stages:

• Egg

• Larvae: free-living, worm-like stage (caterpillar)

• Pupae: tissues/organs break down. Replaced with adult tissues. No movement/feeding. May occur in cocoon

• Adult

• Insect examples

– Moths

– Butterflies