Arthropods Study Guide

Study Guide: Arthropods

phylum Arthropoda

  • Largest and most diverse group in the animal kingdom (~80% of all species)

  • Found in nearly every habitat (land, water, air)

Characteristics

  • Exoskeleton: Hard outer covering made of Chitin

  • Segmented body: Body divided into sections (tagmata)

  • Coelomate

  • Jointed appendages: Legs, antennae, etc.

  • Bilateral symmetry

  • Molting (ecdysis): Growth requires shedding exoskeleton

Body Regions (Tagmata)

Varies by group:

  • Head, thorax, abdomen (e.g., insects)

  • Cephalothorax + abdomen (e.g., spiders, crustaceans)

 Organ Systems

  • Circulatory: Open system (hemolymph instead of blood)

  • Respiration:

    • Gills (aquatic)

    • Tracheal system (insects)

    • Book lungs (arachnids)

  • Nervous system: Brain + ventral nerve cord

  • Excretion: Malpighian tubules (insects)

Major Groups (Classes/Subphyla)

Insects (Class Hexapoda)

  • 3 body parts: head, thorax, abdomen

  • 6 legs, often wings

  • Examples: beetles, butterflies, ants

Arachnids (Class Arachnida)

  • 2 body parts: cephalothorax + abdomen

  • 8 legs, no antennae

  • Examples: spiders, scorpions, ticks

 Crustaceans (Subphylum Crustacea)

  • Mostly aquatic

  • Gills, 2 pairs of antennae

  • Examples: crabs, lobsters, shrimp

Myriapods (Centipedes & Millipedes)

  • Many body segments

  • Centipedes: 1 pair of legs/segment (predators)

  • Millipedes: 2 pairs of legs/segment (detritivores)

Development

  • Metamorphosis (common in insects):

    • Complete: egg → larva → pupa → adult (eg. butterfly)

    • Incomplete: egg → nymph → adult (eg. grasshopper)

  • Ecological roles: pollination, decomposition, food source

  • Economic impact:

    • Helpful: bees (pollination)

    • Harmful: pests, disease vectors (e.g., mosquitoes)

Insects have 

  • Jointed legs + exoskeleton = defining traits

  • Must molt to grow

  • Most diverse animal phylum

Open circulatory system

Beetles — Order: Coleoptera

  • Key traits: Hardened front wings (elytra) that cover flying wings

  • Mouthparts: Chewing

  • Examples: Ladybugs, scarab beetles, fireflies

Butterflies & Moths — Order: Lepidoptera

  • Key traits: Scaly wings, often colorful

  • Mouthparts: proboscis for nectar

  • Examples: Monarch butterflies, silk moths

  • Notes: Complete metamorphosis (caterpillar → adult)

Ants, Bees & Wasps — Order: Hymenoptera

  •  

  • Mouthparts: Chewing (some also lap nectar)

  • Examples: Honeybees, ants, yellowjackets

  • Notes: Many are important pollinators or predators

True Flies — Order: Diptera

  • Key traits: One pair of wings (second pair reduced to halteres for balance)

  • Examples: Houseflies, mosquitoes, fruit flies

🦗 Grasshoppers & Crickets — Order: Orthoptera

  • Key traits: Long hind legs for jumping

  • Mouthparts: Chewing

  • Examples: Grasshoppers, locusts, crickets

  • Notes: Incomplete metamorphosis

 

Dragonflies & Damselflies — Order: Odonata

  • Mouthparts: Chewing (predatory)

  • Examples: Dragonflies, damselflies

  • Notes: Aquatic larvae (nymphs)