Phylum ArthropodaPhylum Arthropoda

• General characteristicsGeneral characteristics

– largest group by sheer numbers – total largest group by sheer numbers – total number exceeds that of all other kinds of number exceeds that of all other kinds of animals combinedanimals combined

– jointed jointed appendagesappendages – extensions of the body – extensions of the body including legs and antennaeincluding legs and antennae

– the body is segmented – a pair of appendages the body is segmented – a pair of appendages is usually attached to each segmentis usually attached to each segment

• body is usually divided into:body is usually divided into:

– headhead

– thorax – wings and walking legs thorax – wings and walking legs attach hereattach here

– abdomen – also divided into segmentsabdomen – also divided into segments

– some have the head and thorax fused some have the head and thorax fused to form a to form a cephalothoraxcephalothorax (spiders, (spiders, crayfish)crayfish)

Cephalothorax

HeadThorax

Abdomen

Walking legs

Mouthparts (feeding)Pincer (defense)

• have an have an exoskeletonexoskeleton – hard external – hard external covering for protection and support – covering for protection and support – made mostly of made mostly of chitinchitin

– exoskeleton does not grow and body exoskeleton does not grow and body enlargesenlarges

– exoskeleton must be shed periodically to exoskeleton must be shed periodically to allow growth – allow growth – moltingmolting

– new exoskeleton is soft – arthropod is new exoskeleton is soft – arthropod is vulnerable until it hardensvulnerable until it hardens

– also susceptible to desiccation (drying also susceptible to desiccation (drying out) out)

Cephalothorax

HeadThorax

Abdomen

Walking legs

Mouthparts (feeding)Pincer (defense)

• open circulatory system – blood drains into sinusesopen circulatory system – blood drains into sinuses• distinct head, often with compound eyes (eye has distinct head, often with compound eyes (eye has

thousands of individual visual units each with its own thousands of individual visual units each with its own lens and retina) – highly sensitive to light, good at lens and retina) – highly sensitive to light, good at detecting motion, can form only crude images detecting motion, can form only crude images

• many have wingsmany have wings

• most respire through most respire through tracheaetracheae – network of – network of fine tubes that carry air directly to the cells – fine tubes that carry air directly to the cells – air enters through pores called air enters through pores called spiraclesspiracles

Classification:Classification:• Subphylum Trilobita – extinct organismsSubphylum Trilobita – extinct organisms

• Subphylum Crustacea – crayfish, lobster, Subphylum Crustacea – crayfish, lobster, pillbugs, copepodspillbugs, copepods

– exoskeleton contains calcium carbonateexoskeleton contains calcium carbonate

• Subphylum Cheliceriformes – spiders, Subphylum Cheliceriformes – spiders, scorpions, ticks, mitesscorpions, ticks, mites

• Subphylum Myriapoda – centipedes and Subphylum Myriapoda – centipedes and millipedesmillipedes

• Subphylum Hexapoda – the insectsSubphylum Hexapoda – the insects

Subphylum TrilobitaSubphylum Trilobita

Subphylum CrustaceaSubphylum Crustacea

Subphylum CheliceriformesSubphylum Cheliceriformes

Subphylum MyriapodaSubphylum Myriapoda

Subphylum HexapodaSubphylum Hexapoda

Class Arachnida – spiders, scorpions, and mites

cephalothorax and abdomen Class Arachnida – spiders, scorpions, and mites

cephalothorax and abdomen Intestine

HeartDigestivegland

Ovary

Anus

Spinnerets

Silk gland

Gonopore(exit for eggs) Sperm

receptacle

Book lung

Chelicera Pedipalp

Poisongland

Eyes

Brain

Stomach

Class Arachnida Class Arachnida • respire through spiracles – air passes to the respire through spiracles – air passes to the book book

lungslungs (sacs in the abdomen that look like pages in a (sacs in the abdomen that look like pages in a book) book)

Book lung

Class ArachnidaClass Arachnida

• Most have 8 simple eyes, some have 4 or 6Most have 8 simple eyes, some have 4 or 6

Class ArachnidaClass Arachnida• have have spinneretsspinnerets – produces thread for webs, – produces thread for webs,

protecting eggs, catching preyprotecting eggs, catching prey• 4 pairs of walking legs4 pairs of walking legs• no jaw – they suck food inno jaw – they suck food in

Spinnerets

Class InsectaClass Insecta• entomologyentomology – study of insects – study of insects• head, thorax, and abdomenhead, thorax, and abdomen• usually have 6 legsusually have 6 legs• thorax may have a pair of wingsthorax may have a pair of wings

Class InsectaClass Insecta

• largest group of animals – very successful largest group of animals – very successful because:because:

– small sizesmall size

– high rate of reproductionhigh rate of reproduction

– capable of flightcapable of flight

– can occupy almost all types of habitatscan occupy almost all types of habitats

– classified by number and type of wingsclassified by number and type of wings

MetamorphosisMetamorphosis

• metamorphosismetamorphosis – change from juvenile form – change from juvenile form to adult formto adult form

– incomplete metamorphosisincomplete metamorphosis – – nymph nymph hatches from egg almost a miniature hatches from egg almost a miniature version of adult (without wings)version of adult (without wings)

• complete metamorphosiscomplete metamorphosis – four stages – four stages

– eggegg

– larva (worm-like)larva (worm-like)

– pupa (cocoon)pupa (cocoon)

– adult adult

(a) Larva (caterpillar)(b) Pupa

(c) Later-stage pupa (d) Emerging

adult

(e) Adult