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