Arthropods
Week 6
Phylum: Arthropoda
• Common name = arthropods
• Ex. Insects, spiders, crabs, shrimp, centipedes,
lobsters, ticks
Monday
Arthropods
• Arthropods have:
– Segmented body
• Head
⇛ Cephalothorax
• Thorax
• Abdomen
– Tough exoskeleton made of chitin
– Jointed appendages
Evolution of Arthropods
• Led to
– Fewer appendages
– Few segments
– Highly specialized appendages
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Antennae
Pincers
Walking legs
Flippers
Claws
Feeding
• Herbivores, carnivores, omnivores
• Bloodsuckers, filter feeders, detritivores,
parasites
• Mouthparts range from pinchers to fangs to
sickle-shaped jaws depending on diet
Respiration
• Terrestrial
– Breathe thru a network of branching tracheal
tubes
– Air enters through spiracles = little openings along
body
– Spiders uses book lungs
• Aquatic
– Featherlike gills
– Horseshoe crabs have book gills
Circulation
• Open circulatory system
• Well-developed heart
Excretion
• Terrestrial
– Malpighian tubules = saclike organs that extract
wastes from the blood and add them to feces
(digestive wastes)
• Aquatic
– Diffusion
Response
• Well-developed nervous system
• All have a BRAIN
Movement
• Muscles are attached to exoskeleton
• Pull of muscles against exoskeleton allows
arthropods to move
• All have jointed appendages
Reproduction
• Terrestrial
– Internal fertilization
• Aquatic
– Internal or external fertilization
Growth and Development
• Exoskeletons DO NOT GROW, arthropods must
MOLT
• Molting = arthropod sheds entire exoskeleton
and makes a new larger one
• Molting arthropods are vulnerable and hide
until they are done
Crustaceans
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Primarily aquatic
Crabs, shrimps, lobsters, crawfish, barnacles
2 pairs of branched antennae
2 or 3 body segments
Chewing mouthparts = mandibles
Tuesday
Associated Vocabulary
• Cephalothorax = fused body segment
consisting of head and thorax
• Abdomen
• Carapace = part of exoskeleton that covers the
cephalothorax
• Mandible = biting, grinding mouthpart
• Chelipeds = claws
• Swimmerets = flipper-like appendages for
swimming
Chelicerates
• 2 body segments
• Most have 4 pairs of walking legs
• Horseshoe crabs, spiders, ticks, scorpions
From Prentice Hall Biology, 2006
Eyelash
mites
Demodex folliculorum
Brown Recluse
Black Widow
Associated Vocabulary
• Chelicerae = mouthparts with fangs for
stabbing and paralyzing prey
• Pedipalps =mouthparts for grabbing prey
• Book lungs
• Book gills
• Spinnerets = organs in spiders that contain silk
glands for spinning webs
Uniramians
• Contains more species than all other animal
groups combined!
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Jaws
1 pair of antennae
Unbranched appendages
Insects, centipedes, millipedes
Centipedes and Millipedes
• Millipedes
– Highly segmented body
– 2 pairs of legs per segment
– Live under rocks and decaying logs
– Roll up or secrete toxins for defense
• Centipedes
– 1 pair of legs per segment
– Carnivorous and venomous
– Live under rocks or in soil in humid areas
Insects
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3 body segments = head, thorax, abdomen
3 pairs of legs
1 pair of antennae
1 pair of compound eyes
2 pairs of wings
Wednesday
Insects are the
largest class of
animals!
Response to Stimuli
• Compound eyes with many lenses detect tiny
movements and color changes
• Chemical receptors on mouthparts, legs and
antennae (taste/smell)
• Well-developed ears (grasshoppers have ears
on their legs!)
Adaptations for Feeding
• 3 pairs of appendages used as mouthparts
– Mandibles to saw/grind (ex. ant)
– Tube-like mouthpart to suck nectar (ex. moth)
– Sponge-like mouthpart to lap up food (e. fly)
• Digestive enzymes in saliva
– Bee saliva changes nectar from flowers into honey
Movement and Flight
• 3 pairs of legs
– Walking, jumping, capturing/holding prey
– Many species have spines or hooks on legs
• 2 pairs of wings made of chitin
• Evolution of flight allowed insects to disperse
long distances and colonize many habitats
Metamorphosis
• Process of changing shape and form
– Complete metamorphosis
• Egg-larva-pupa-adult
• Larva looks nothing like adult
– Incomplete metamorphosis
• Egg-nymph-adult
• Nymphs look like adults
Advantage = larva
and adults don’t
compete for
resources
Insects and Humans
• Beneficial
– Honey
– Wax
– Pollination
– Silk
– Food
• Harmful
– Damage wood
– Damage clothes
– Stings
– Crop damage
– Disease
Insect Communication
• Audio
– Crickets
• Visual
– Fireflies
• Chemical
– Bees
– Pheromones
Insect Societies
• Society = a group of closely related animals of
the same species that work together for the
benefit of the whole group
– Bees
– Ants
– Termites
• Castes = groups of individuals that perform
specific functions