http www tolweb orgArthropoda2469 mandibulata Phylum Arthropoda Subphylum

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 • 1 st 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

Order Acari: The ticks Lyme’s Disease • deer tick = Ixodes scapularis is a vector for the spirochete, Borrelia burgdorferi, from whitefooted mice (reservoir host) and people

Order Scorpiones • Most ancient arachnid (and therefore most primitive terrestrial arthropod) • Also the largest arachnid is a scorpion (18 cm)

Class Arachnida, Order Scorpiones A delicacy in Bankok, Thailand

Opisthosoma Prosoma Mesosoma Metasoma Eyes Chelicera Telson Chela Pedipalp Aculeus

Class Arachnida: Order Aranea (Spiders) • 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

book lung

O. Pseudoscorpiones No stinger Dispersal by phoresy (hitchhike on houseflies) Poison in chelae for immobilizing prey

Order Amblipygi First legs held out while they scurry sideways • serve as tactile and chemoreceptors Tailless whip scorpions are common in Costa Rica

Order Opiliones

Subphylum Mandibulata • Class Myriapoda – Order Chilopoda – Order Diplopoda • Class Insecta (Hexapoda) – 33 orders • Class Crustacea – 6 subclasses

Myriapoda • 1 st head segment bears antennae • 2 nd head segment vestigial (no antennae) – In crustacea this segment bears 2 nd 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 legs Defensive Sensory Aggressive

Diplopoda • Diplosegments give the appearance of 2 pairs of legs per segment • Lack poison claws • Some produce cyanide defensive secretions