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Announcements

Web pages up (see my home page)Today’s reading (mostly on reserve)

– Anderson: pages on lecture topichandout•pp. 289-299 only for the big picture!

– Text: pp 178-183, 202-21

Phylum Onychophora andTardigrada

Phylum Onychophora andTardigrada

• Like arthropods, both groups have– Reduced coelom (body cavity)– Open circulatory system– Outer covering (cuticle)

• Onycophorans sister group to arthropods• Tardigrades can live in extreme

environments

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Introduction to PhylumArthropoda

Introduction to PhylumArthropoda

• Very old group of animals (>500 MYBP)• Oldest fossils in ocean• Highly diverse in water and on land.• Four major living groups, others extinct

Arthropod Features

• Body plan

– bilateral symmetry– metamerism

– paired jointed appendages– tagmata (tagma)

– exoskeleton

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Arthropod Features

• Jointed appendages•sensory structures•feeding appendages•locomotion•reproductive structure

Uniramous or Biramous

Arthropod Features

• Eyes

Simple CompoundOne lens, records daylength many lenses, detects movement

Arthropod Features

• Physiology•body cavity: hemocoel•circulatory system: open with dorsalheart, not used for gas exchange

•nervous system: paired ventral nervecords

•respiratory systems: gills ortracheal system

•excretory systems: Diverse.Malpighian tubules found in mostterrestrial forms

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Arthropod Features– Growth through molting

Arthropod Features• Reproduction

– internal fertilization

Adaptations toTerrestrial Life

• Internal fertilization

• Tracheal system

• Excretory system

• Waxy cuticle (Hexapoda)

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Living Groups of Arthropods• Superclasses

– Crustacea

– Chelicerata– Myriapoda– Hexapoda

Superclass Crustacea

Crustacean Features

– Diverse body plans with differentpatterns of segment fusion

– 2 pair antennae– Mandibles– biramous appendages– exoskeleton is chitin and calcium– gills

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Biramous appendages

Terrestrial Crustaceans• Sowbugs, pillbugs

Superclass Chelicerata

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Chelicerate Features I

– variable morphology based on commonbody plan• cephalothorax

– Anterior prosoma: bears limbs– Posterior opithosoma

– six pairs of appendages• chelicerae• pedipalps• walking legs

– Appendage morphology• most appendages uniramous• a few marine forms show biramous appendages

Chelicerate Features II– NO antennae

– book gills or book lungs– Possess chelicerae for feeding– juveniles look like adults

– generally predaceous, someparasites

Chelicerate Groups• Pycnogonida

• Merostomata

• Arachnida

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Pycnogonida

• Ancient group, reduced abdomen

MerostomataAlso ancient, compound eyes

Arachnida

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Arachnida• Diverse on land• Waxy cuticle• Vary in size of abdomen vs throax• Predaceous or parasitic

Superclass Myriapoda

Myriapod Features

– little tagmatization– many segments- growth throughaddition

– uniramous– numerous pairs of legs– juveniles look like adults– jointed mandibles

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Myriapod Groups

Diplopoda: Millipedes

Chilopoda: Centipedes