Chapter 16

The Arthropods

Phylum Arthropoda

Largest phylum in Kingdom AnimaliaAnthropoda means “jointed feet”Includes lobsters, spiders, scorpions, milli-

pedes, and insectsCan be harmful or helpfulHarmful: destroy crops, eat other animals’

food, spread diseasesHelpful: studied by engineers; control the

numbers of harmful arthropods; help plants reproduce; make wax, honey, medicine, and silk

Phylum Arthropoda

All arthropods have:Exoskeleton – their bones are outside of their body

Chitin – allows the bones to be tough and flexible – they bend with-out breaking

Arthropods molt – as they grow, their exoskeleton becomes too small – they outgrow the exoskeleton and throw it away

Jointed appendages – their legs and feet have joints (bend)Body segmentation – most have 3 parts to their bodies

Head Thorax (chest) Abdomen (belly)

Open Circulatory System – they have a heart, but the blood goes into the body parts after leaving the heart (not veins)

Ventral Nervous System – Ganglia (nerves) are located near the legs and connected to the brain by one cord

Phylum Arthropoda

Nervous System Anatomy

Brain – located in the headGanglia – nerves in the legsVentral Nerve Cord – big nerve that connects the

brain and the gangliaAntennae – come out of the head and do taste, smell,

and touchCompound eyes – insects and crustaceans have these

– able to see all around, not just a few directions______ OR_________

Simple eyes – able to see very little, usually just light and dark

Nervous System Anatomy

Subphylum Crustacea

Lobsters, crabs, crayfish, shrimpKingdom Animalia, Subkingdom Invertebrates, Phy-

lum Anthropoda, Subphylum CrustaceaUsually live in the waterCarapace – the back plate of a lobster (the front has 6

plates)Scavengers: they eat anything! They grind their food

into powder using the gastric mill.They can regenerate (grow new parts)Reproduce sexually – male gives sperm to the female

in the fall, female lays eggs in the spring that hatch in the summer

Subphylum Crustacea

Subphylum Chelicerata

3 classes: Arachnida is the most important classArachnids have:

8 legs – 2 of these are pedipalps (legs used for sensing and mating instead of walking)

2 major segmentsCephalothorax (head-chest)abdomen

No antennae or mandibles (jaws)Have chelicerae instead (mouth that looks like fangs)

Respiration by book lungsBreathe through their stomachs

Usually 4 pair of simple eyes (8 eyes)Reproduce sexually – females are usually larger than

males

Subphylum Chelicerata

Scorpions, mites, and ticks

Other Arachnids

Class Insecta

80% of all animals are insects (bugs)There are 31 orders under Class InsectaStructure of Insects:

Three pairs of legs (six legs)Usually have wings3 segments to the body

HeadThorax (chest)Abdomen

One pair of sensory antennae (2 of them)

Class Insecta

M0st insects have 2 pairs (4) wingsKinds of wings:

Membranous wings: thin, transparent (see through) – most common kind of wing - like a dragonfly or a bee

Scale-covered wings: butterflies and moths

Wings of Insects

Continued:Leatherlike wings: extra set of wings that pro-

tects the wings used to fly – like a cover for wings – grasshoppers have these

Horny wings: ladybug wings – thick, protect the smaller wings, cover the back of the bug

Wings of Insects

Mouth: Upper lip - labrumMandibles - used for chewingMaxillae – put food into the mouthLower lip – labium

Stomach:Foregut – behind the mouth – this is where salivary

glands get the food wet with spit before going to the gizzard to be ground up into powder

Midgut – where the stomach is – gastric ceca put more digestive juices onto the food

Hindgut – place right before the food is excreted (pooped)

Digestion (eating) of Insects

Respiration: insects breathe in their ab-domens through tubes called spiracles

Circulation: the insects heart pumps blood into the abdomen, where it covers the organs – no veins

Excretion: Malpighian tubules are straws that pull nitrogen out of the insect and put it into the intestines, where it will become poop

Reproduction: Sexual reproductionThe male puts sperm in the femaleThe female then lays eggs that will hatch later

Respiration, Circulation, Excretion and Reproduction

Metamorphosis means changing from a baby to an adult

There are two kinds of metamorphosis:Incomplete metamorphosis (3 stages)

Grasshoppers, cicadas, and true bugsEggNymph (teenager – looks like a small adult) – only for

insects that stay on land (cicadas)ORNaiad – teenager that doesn’t look like the adult and

lives in the water (grasshoppers)Adult – the bug

Metamorphosis in Insects

Incomplete Metamorphosis

Complete metamorphosis (4 stages)Most insects – butterflies, flies, beetles, mosquitoesEggsLarva – like a little worm (maggots, grubs, wig-

glers, caterpillars) – childhood bugPupa – teenager insect – usually inside a case

called a cocoonAdult – the bug

Metamorphosis

Complete Metamorphosis