Classification of Invertebrates

Introduction

• Focus on classifying invertebrates.
• Invertebrates: organisms without an internal backbone or skeleton.
• More diverse and numerous than vertebrates.

Characteristics of Invertebrates

• No internal skeleton; may have an exoskeleton.
• Wide range of organisms, including arthropods, mollusks, echinoderms, cnidarians, sponges, and worms.

Major Groups of Invertebrates

1. Arthropods

• Characteristics:
  • Jointed legs.
  • Hard shell or exoskeleton.
  • Exoskeleton is shed as they grow.
• Subgroups:
  • Insects:
    • Body in three segments: head, thorax, abdomen.
    • Three pairs of legs.
    • Examples: ants, butterflies, grasshoppers, beetles.
  • Arachnids:
    • Body in two segments: cephalothorax, abdomen.
    • Four pairs of legs (eight legs total).
    • Examples: spiders, scorpions, ticks.
  • Crustaceans:
    • Aquatic arthropods.
    • Examples: crabs, lobsters, prawns.
  • Centipedes and Millipedes:
    • Centipedes: one pair of legs per body segment.
    • Millipedes: two pairs of legs per body segment.

2. Mollusks

• Characteristics:
  • Soft bodies, often with hard shells.
• Subgroups:
  • Cephalopods:
    • Head connected to legs.
    • Examples: squid, octopus, nautilus.
  • Gastropods:
    • Stomach foot structure (body connected to foot).
    • Examples: slugs, snails.
  • Bivalves:
    • Two-part shell.
    • Examples: clams, oysters.

3. Echinoderms

• Characteristics:
  • Spiny skin.
  • Radially symmetrical.
• Examples:
  • Sea stars, sea urchins, sea cucumbers.

4. Cnidarians

• Characteristics:
  • Stinging capabilities.
  • Hollow soft bodies.
• Examples:
  • Jellyfish, anemones, coral polyps.

5. Sponges (Porifera)

• Characteristics:
  • Porous bodies.
  • Filter nutrients from water.

6. Worms

• Subgroups:
  • Annelids (Segmented Worms):
    • Segmented body structure.
    • Example: earthworms.
  • Platyhelminthes (Flatworms):
    • Thin, flat bodies.
  • Nematodes (Roundworms):
    • Cylindrical bodies with tapered ends.

Conclusion

• Invertebrates encompass a vast range of organisms with diverse characteristics.
• Key groups include arthropods, mollusks, echinoderms, cnidarians, sponges, and worms.
• Important to understand the unique features of each group for classification purposes.