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Chapter 9 Phylum Arthropods
“joined appendages”
Characteristics of all Arthropods
• Hard exterior (exoskeleton)• Joined appendages• Highly evolved nervous systems• Segmented body• 2 main groups– Chelicerates and mandibulates
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
• 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
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/watch
?v=4QIgW639Oog&safety_mode=true&persist_safety_mode=1&safe=active
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_mode=1&safe=active
• Digestion– Variety of feeding
habits(depend on species)• Majority are predatory
scavengers– Large inverts are prey for
most» Ex Alaskan king crab
feed on bivalves» Hermit Crabs and
shrimp-scavengers feed on detritus
» Fiddler crabs-deposit filter feeders
• Reproduction– Separate sexes/internal
fertilization• Males special appendage
modified for holding onto female and depositing sperm.
• Eggs are incubated by female; larvae stage when hatched
Crayfish Anatomy
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
• 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
– 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
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
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
Compete for space* as a scientist, how would you determine population density of the barnacle
species on this dock post?