Phylum Arthropods are the most abundant animals, making up over 83% of all animal species. They have been highly successful due to their hard exoskeleton, jointed appendages, ability to live in extreme environments, and filling many ecological niches. All arthropods have in common an exoskeleton, jointed limbs, segmented bodies, and highly evolved nervous systems. The two main groups are chelicerates and mandibulates.

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