Lecture 3-3: Invertebrates - Phylum Cnidaria and Beyond

Recap of Phylum Cnidaria

• Class Cubozoa

  • Known as box jellyfish.
  • Distinct from other jellyfish (Class Scyphozoa) genetically and physiologically.
  • Characteristics:
    • Four tentacle emergence points (hence the 'box' shape).
    • Smaller than most jellyfish but more dangerous.
    • Have simple eyes but no brain.

• Class Hydrozoa

  • Includes marine and freshwater species.
  • Body Plans:
    • Can be solitary polyps or form large colonies.
    • Some have a medusa body plan, like peach blossom jellyfish.
    • Example: Portuguese Man o' War is a colony of polyps functioning as one.

Introduction to Bilateria

• Characteristics:
  • Animals with bilateral symmetry and triploblastic (three cell layers) structure.
  • Groups include Protostomes and Deuterostomes.

Protostomia

• Clades:
  • Lophotrochozoa:
    • Members have either a lophophore (ciliated feeding structure) or trochophore larvae.

Phylum Platyhelminthes (Flatworms)

• Characteristics:
  • Acoelomate body plan.
  • Complex organ systems, including nervous, digestive, and excretory systems.
  • No circulatory or respiratory systems—use diffusion for gas exchange.
• Types:
  • Free-living and parasitic (e.g., tapeworms, liver flukes).

Phylum Rotifera (Rotifers)

• Characteristics:
  • Microscopic aquatic animals.
  • Pseudocoelomates with a hydrostatic skeleton.
  • Corona and mastax for feeding.

Phylum Nemertea (Ribbon Worms)

• Characteristics:
  • Coelomate with a closed circulatory system.
  • Have a retractable proboscis stored in a rhynchocoel.

Phylum Mollusca

• Characteristics:
  • Morphological Features:
    • Foot for movement/anchorage.
    • Mantle that may secrete a shell.
  • Most have a radula for feeding.
  • Coelomates, mostly with an open circulatory system.
• Classes:
  • Class Polyplacophora (Chitons): Marine, have eight-plate shells.
  • Class Bivalvia (Clams, Oysters): Aquatic filter feeders with no radula.
  • Class Gastropoda (Snails, Slugs):
    • May have shell; undergo torsion in development.
  • More classes to be discussed in the next lecture.