1. Chapter 9
Phylum Arthropods
“joined appendages”

2. Abundant!
• >83% of animals found
have been arthropods
• The great survivors
– Over 500 million species

3. Incredibly adapted
• Successful:
– Been around for over
500 million years
– Large numbers
– Live in extreme
conditions
– Ecological niches
• Gammarus wilkitzkii
• Scolopendra gigantea

4. Characteristics of all Arthropods
• Hard exterior (exoskeleton)
• Joined appendages
• Highly evolved nervous systems
• Segmented body
• 2 main groups
– Chelicerates and mandibulates

5. THE EXOSKELETON
• Provides
– Structural support
– Protection
– Prevention of water loss
– System for muscle
attachment and movement
• Gas exchange
• Soft tissue for joints
• Molting: shedding of
exoskeleton to allow growth

6. Adaptive features
• Tagmatization
– Specialized segments of
body
• Feeding
• Locomotion
• Digestion
• Sensory perception etc.
• Metamorphosis
– Radical change in body
– Reduces competition
between adults and
larva

7. Chelicerates
• Primitive Arthropods
• Characteristics
– 6 pairs of appendages
• 1 oral appendage
(chelicerae) used for feeding
– Lack actual mouth parts for
chewing so “suck up
predigested food”
– Cephalothorax-largest
– Abdomen –contains gills

8. • Representative species
– Horseshoe crabs and sea spiders
• Reproduction
– Sexual: separate sexes
• Sea spiders: males carry fertilized eggs ( only marine
invert to do this!!!!!)
• Horseshoe crabs: external fertilization; females lay
eggs in sand and when hatch carried to sea by high tide
• Digestion
– Horseshoe crab: scavengers; will eat anything
– Sea spiders: carnivores; feed on cnidarian juice!!

9. Mandibulates (Crustaceans)
• Characteristics
– Mandible: pair of appendages at anterior end
used for feeding
– 3 main body regions: head, thorax and abdomen
– 2 pairs of antennae
– Remaining appendages used for locomotion
– Molting: as animals grows, new exoskeleton is
formed and old one is shed
• The shell does not grow with the crustacean

10. Crustaceans
• Reproduction • Digestion
– Separate sexes/internal – Variety of feeding
fertilization habits(depend on species)
• Males special • Majority are predatory
appendage modified scavengers
for holding onto – Large inverts are prey for
female and most
depositing sperm. » Ex Alaskan king crab
• Eggs are incubated by feed on bivalves
» Hermit Crabs and
female; larvae stage shrimp-scavengers
when hatched feed on detritus
» Fiddler crabs-deposit
filter feeders

11. Crustaceans
– Reproduction
• Sexual
– Separate sexes
– Some species internal fertilization/ others spawners
– Life cycle 6 months to 6 years
• Copepods
– Most abundant of zooplankton
– Suspension feeders
– Carnivorous
– Sexual reproduction

12. Class Cirripedia
“barnacles”
• Characteristics
– Only sessile crustaceans
– Shell of calcium carbonate
• Digestion
• Filter feeders: use appendage “cirriped”
• Reproduction
– Hermaphrodites: cross fertilize
– Larvae move until finds a substrate and metamorphoses
into adult-> remain sessile

13. The Food Chain
• Ecological Role
– Main diet of certain marine mammals
• Keystone species of Antarctic food web
• Blue whales eat 40 million krill a day
– So why haven't krill gone extinct?
– Krill

14. Ecological Roles of Arthropods
• Essential links in food chains
• Nutrient recycling
• Food sources for humans
and many other animals
• Symbiotic relationships
– Some can remove parasites –
cleaner shrimp
• Some have become invasive
when introduced

15. Do they look familiar?

16. Phylum Arthropoda: Subphylum
Crustacea Trilobita Chelicerata Atelocerata

17. Subphylums
• Trilobita • Crustacea
– Extinct – Lobsters
– Shrimp
• Chelicerata – Crabs
– Horseshoe crab – Water fleas
– Sea spiders – Copepods
– Spiders – Barnacles
– Sowbugs
– Scorpions
• Atelocerata
– Harvestmen
– Millipedes
– Mites and ticks – Centipedes
– Hexapods