Notes for Chapter 18:
Overview of Arthropods (Jointed Skeletons)

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or back to Chapter 17
or ahead to Chapter 19

Chapter 18 Assignment: All; RQ-18: 1-6, 9
Next: Ch. 19: 389-399, 406-409; RQ-19: 1, 4-9
Then: Ch. 20: 411-427, 432-437; RQ-20: 1-4, 6, 7, 9, 10, 18

Introduction: A Suit of Armor


Source of Image

Featured organism: Scorpion
   More Links: 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12

I. Arthropods
    More Links or Overview of Main Groups


Arthropod Diversity
  be somewhat familiar with the underlined groups on arthropod hand-out
  know basic body plan of 4 groups: chelicerates, myriapods, crustaceans, insects


Arthropoda (simplified)
     Trilobita (trilobites)
     Chelicerata (see cladogram p. 386)
         Pycnogonida (sea spiders)
         Clade 1
            Merostomata (horseshoe crabs)
            Arachnida (scorpions, spiders, mites)
  Mandibulata (mouthparts are mandibles)
Myriapoda (centipedes and millipedes)
     Crustacea (see cladogram p. 408)
         Remipedia (remipedes)
         Clade 2
            Cephalocarida (cephalocarids)
            Clade 3
               Branchiopoda (brine shrimps)
               Clade 4
                  Maxillopoda (copepods and barnacles)
                  Malacostraca (isopods and decapods)

II. Body Plan

Key Term: exoskeleton, cuticle layers, ecdysis (molting), ecdysone, segmentation (contrast annelids), tagmatization

Why are arthropods so diverse and abundant?

1. versatile exoskeleton
  •protects while permitting mobility
  •cuticle secreted by epidermis (p. 644)
  •thick procuticle – chitin/protein
    – exocuticle (often with calcium salts)
    – endocuticle (soft/flexible)
  •thin epicuticle – waxy
  •cuticle is light/waterproof/nonexpanding
  •growth requires molting (pp. 397-398)
  •molting process called ecdysis
  •hormone is ecdysone

2. Segmentation/appendages specialized
  •hollow limbs act as levers
  •striated muscles are rapid
  •appendages have sensory hairs
  •others handle food or permit movement

3. Air piped directly to cells (terrestrial species)
  •thin-walled cuticle-lined tubes (trachea)

4. Highly developed sensory organs
  •compound eyes
  •also sense touch, smells, noises, chemicals

5. Complex behaviors
  •both innate and learned

6. Complex life cycles
  •metamorphosis in certain insect groups
  •larvae/adults have separate ecological roles

III. Trilobita (extinct but dominant organisms for nearly 300 My)
   More Links: 1 - 2 - 3

scavengers and predators

IV. Chelicerata (including horseshoe crabs, sea scorpions, and arachnids)

   6 pairs of appendages (chelicerae, pedipalps, 4 pairs walking legs)
   no mandibles, no antennae


   giant sea scorpions (up to 3 m in length)
   horseshoe crabs

Basic features: prosoma (carapace), opisthosoma (abdomen), telson, book gills for respiration

Pycnonida-sea spiders

Arachnida (70,000+ species, including
spiders, scorpions, daddy longlegs, and especially mites)

Basic features: tagmata: cephalothorax and abdomen

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or back to Chapter 17
or ahead to Chapter 19


This page created 10/7/01 © D.J. Eernisse, Last Modified 10/9/01, Links Last Completely Checked 10/5/01