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!!

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

Order Decopoda (“decopods”)

• Representative species– Crabs, lobster, and shrimps

• Characteristics– 5 pairs of walking legs• 1st pair pincers 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 Dissection!!!!!!

Get Ready for Dissection Marine Sciencers!!!!!!!!

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?