http://www.tolweb.org/Arthropoda/2469

mandibulata

Phylum Arthropoda

Subphylum Trilobita

• Common 500 mya (4000 spp) but extinct by 225 mya

• Each body segment had a biramous appendage (inner for walking)

• 3 body tagma

• Compound eyes with ommatidia

Trilobites flourished for 270 million years.They died.

Subphylum Chelicerata

• Include spiders and mites and daddy LL, scorpions, horseshoe crabs

• Lack antennae

• 1st pair of appendages on the prosoma = the chelicerae (adapted for feeding)

Class Xiphosura: Horseshoe crabs

• 4 spp, all marine

• Not true crabs (i.e., not crustaceans)

• head + thorax = prosoma or cephalothorax

• appendages of opisthosoma flattened to become “book gills” for gas exchange

Telson

Class Arachnida• Terrestrial

– Orders: spiders, mites, ticks, scorpions, ddll– 4 pairs of walking legs, one pair of pedipalps

• Head and thorax fused = prosoma– In ticks the prosoma and opisthosoma fuse

= carapace

Lyme’s Disease• deer tick = Ixodes scapularis is a vector for the

spirochete, Borrelia burgdorferi, from white-footed mice (reservoir host) and people

Order Acari: The ticks

Order Scorpiones

• Most ancient arachnid (and therefore most primitive terrestrial arthropod)

• Also the largest arachnid is a scorpion (18cm)

Class Arachnida, Order ScorpionesA delicacy in Bankok, Thailand

Prosoma Mesosoma

Metasoma

Opisthosoma

Eyes

Chelicera

Chela Pedipalp

Telson Aculeus

• Book gills internalized: = book lungs– Spiracles and trachea– Gas exchange does not require blood

• Spiders are specialized predators– Poison glands, hollow chelicerae– Silk glands, web building

• Spinneret are modified appendages• 7 separate silk glands make different kinds of silk

Class Arachnida:Order Aranea (Spiders)

book lung

O. Pseudoscorpiones No stinger

Poison in chelae for immobilizing prey

Dispersal by phoresy(hitchhike on houseflies)

Order Amblipygi

Tailless whip scorpions are common in Costa Rica

First legs held out while they scurry sideways• serve as tactile and chemoreceptors

Order Opiliones

Subphylum Mandibulata

• Class Myriapoda– Order Chilopoda– Order Diplopoda

• Class Insecta (Hexapoda)– 33 orders

• Class Crustacea– 6 subclasses

Myriapoda

• 1st head segment bears antennae• 2nd head segment vestigial (no antennae)

– In crustacea this segment bears 2nd pair of antennae

• Gas exchange by trachea, spiracles on each body segment– Not closable, risk of water loss– Cuticle not waterproof – more water loss

• Excretion by malpighian tubules• Repugnatorial glands on ventrum

Order Chilopoda - centipedes

• Uniramous appendages, one per segment• Spiracles cannot be closed to control water loss

Claws (modified legs) with poison glands for immobilizing prey

mandibles

cephalon

Non-locomotory anal legsDefensive

SensoryAggressive

Diplopoda

• Diplosegments give the appearance of 2 pairs of legs per segment

• Lack poison claws

• Some produce cyanide defensive secretions