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Arthropods
Chapter 28
Arthropod characteristics
• Segmented bodies
• Tough exoskeleton made of chitin
– Multiple shapes and textures
• Jointed appendages: legs and antennae
Arthropod evolution
• Modern arthropods have fewer body
segments and more specialized
appendages.
Fossil of a
Trilobite,
extinct
class of
Arthropod
Fossil of Leanchoilia, Phylum Arthopoda
www.burgess-shale.bc.ca/ gallery/gallery.htm
Feeding
• Herbivores, carnivores, omnivores,
parasites, blood suckers, filter feeders,
and detritovores
• Variety of mouthparts: pincers, fangs,
sickle-shaped jaws, feeding tubes
stag beetle pincers
Respiration
• Most arthropods
– Tracheal tubes: branching network of tubes
that deliver and expel air through spiracles
• Some arthropods (including spiders)
– Book lungs: layers of respiratory tissue
stacked like pages of a book
Circulation
• Open circulatory
system: heart pumps
blood to tissues,
sinuses, and cavities
but does not return to
the heart directly
Excretion
• Malpighian
tubules: saclike
organs that extract
wastes from blood
and then add them
to feces to move
through the gut
Chrysina quetzalcoatli is freed in Cusuco
National Park, leaving a fecal trail
National Geographic
Response
• Sensitive sensory organs (sight, smell,
touch)
• Well-developed nervous system
– Brain
– Ventral nerve cord
– Ganglia: groups of nerve cells
Movement
• Flexor muscles
• Extensor muscles
• Muscle pulling against exoskeleton
enables movement
Reproduction
• Terrestrial arthropods: internal fertilization
– Male places sperm in female
– Sperm sac that female picks up
• Aquatic arthropods: internal or external
fertilization
Growth and development
• Molting: period of
shedding exoskeleton
when outgrown
– Glands secrete
digestive enzymes to
break down
exoskeleton.
– Glands secrete new
exoskeleton.
– Vulnerable stage
Insect molting case left on tree bark
Arthropod subphylums
• Crustaceans
• Spiders and their relatives
• Insects and their relatives
Crustacean characteristics
•
•
•
•
•
•
Two pairs of antennae
Two or three body sections
Mandibles: chewing mouthparts
Body plan: celphalothorax, abdomen, carapace
Barnacles have “lost” appendages.
Decapods have chelipeds and swimmerets.
– Ex: shrimp, lobster, crayfish
The Anatomy of a Crayfish
Section 28-2
Abdomen
Tail
Cephalothorax
Swimmerets
Carapace
First antenna
Mandible
Second antenna
Cheliped
Walking legs
Subphylum Crustacea – hermit crab
Subphylum Crustacea –crab
Subphylum Crustacea – fire shrimp
Chelicerate characteristics
• Four pairs of walking legs
• Chelicerae mouthparts: fangs that sting
and pedipalps that grab prey
• Two body sections: cephalothorax and
abdomen
• Classes: Merostomata (horseshoe crabs)
and Arachnida (spiders, scorpions)
• Spiders have spinnerets, silk glands.
The Anatomy of a Spider
Section 28-2
Cephalothorax
Brain
Abdomen
Pumping
stomach
Heart
Intestine
Ovary
Malpighian
tubules
Eyes
Poison
gland
Anus
Pedipalp
Fanglike
chelicera
Spiracle
Bases of
walking legs
Airflow
Figure 28–9
Book Lung
Spinnerets
Silk glands
Subphylum Arachnida – black widow spider
Scorpion
Gum shoe
spider web
Theridae
family
National Geographic
Photo by Darlyne A. Murawski
Uniramia characteristics
•
•
•
•
Jaws
One pair of antennae
Unbranched appendages
Groups: centipedes, millipedes, insects
Millipede
Centipede
Why insects are evolutionarily
successful
• Flight
• Variety of stimuli responses
• Differential feeding methods between
young and adult
• Different morphology between young and
adult
Insect characteristics
•
•
•
•
•
•
Compound eyes
Some with wings
Three part body plan
Three pairs of legs
Sensitive taste and smell receptors
Three appendages for mouth,
including pair of mandibles
The Anatomy of a Grasshopper
Section 28-1
Compound eye
Brain
Antennae
Digestive
tract
Malpighian tubules
Heart
Reproductive
organs
Ventral View
Legs
Mouth
Salivary
glands
Anus
Ganglia
Tracheal tubes
Nerve
cord
Tracheal
tubes
Spiracles
Figure 28–4
Spiracles
Insect life cycle
• Metamorphosis: process of changing
shape and form from juvenile to adult
stage
– Incomplete: juvenile stage (nymphs) appear
like adults, just smaller
– Complete: juvenile stage (larvae) becomes
pupa, final stage before becoming an adult
Section 28-3
Metamorphosis
Adult
Eggs
Adult
Eggs
Incomplete
Metamorphosis
Complete
Metamorphosis
Larva
Adult
Nymph
Nymph
Immature
Nymph
Adult
Figure 28–18
Larva
Pupa
Insects and humans
• Although they can be a nuisance or pest,
insects are significant to agriculture.
• They facilitate flower pollination.
Insect communication and societies
• Chemical cues:
pheromones
• Visual cues: light,
flight patterns
• Some insects form
societies where
castes, groups of
individuals, perform
specific tasks.
Polyphemus moth
Pheromone chemical: (E,Z)-6,11Hexadecadienyl acetate
National Geographic
Image by Joseph Scheer
Subphylum Insecta – lady bug
Subphylum Insecta – bee moth