chapter 9 arthropods zoology
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Chapter 9 Phylum Arthropods
“joined appendages”
Abundant!
• >83% of animals found have been arthropods
• The great survivors – Over 500 million species
Incredibly adapted
• Successful: – Been around for over
500 million years – Large numbers – Live in extreme
conditions – Ecological niches
• Gammarus wilkitzkii • Scolopendra gigantea
Characteristics of all Arthropods
• Hard exterior (exoskeleton)• Joined appendages• Highly evolved nervous systems• Segmented body• 2 main groups– Chelicerates and mandibulates
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
Adaptive features
• Tagmatization– Specialized segments of
body• Feeding• Locomotion• Digestion • Sensory perception etc.
• Metamorphosis– Radical change in body – Reduces competition
between adults and larva
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
Crustaceans• 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
• 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
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
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
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
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
Do they look familiar?
Phylum Arthropoda: Subphylum
Crustacea Trilobita Chelicerata Atelocerata
Subphylums
• Trilobita– Extinct
• Chelicerata– Horseshoe crab– Sea spiders– Spiders – Scorpions– Harvestmen – Mites and ticks
• Crustacea – Lobsters – Shrimp– Crabs– Water fleas– Copepods– Barnacles– Sowbugs
• Atelocerata– Millipedes– Centipedes– Hexapods
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