1. Chapter 9
Phylum Arthropods
“joined appendages”

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

3. 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

4. • 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!!
• http://www.youtube.com/watch?v=wA-NoH_G330

5. 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
• http://www.youtube.com/watc
h?v=4QIgW639Oog&safety_mo
de=true&persist_safety_mode=
1&safe=active

6. Order Decopoda (“decopods”)
• Representative species
– Crabs, lobster, and shrimps
• Characteristics
– 5 pairs of walking legs
• 1st pair pinchers for food and defense
• http://www.youtube.com/watch?v=flnMoSghUzs&feature=related&safety_mode=true&persist_safety_m
ode=1&safe=active

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

8. Crayfish Anatomy

11. Order Euphausiacea
• Representative species
– Krill
• Characteristics
– Pelagic
– Shrimp-like (3-6 cm)
– Photospheres: Organ producing bioluminescent
• Used to attract mates; so what is reproduction?
– Can molt so quick that will “jump out of their shells!
• Digestion- filter feeders; eat zooplankton and
diatoms

12. • 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?
– http://www.youtube.com/watch?v=OPMQaP-
Yj1Y&safety_mode=true&persist_safety_mode=1
&safe=active

13. – 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

14. 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

16. 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

17. Compete for space
* as a scientist, how would you determine population density of the barnacle
species on this dock post?