Invertebrate Phyla: Platyhelminthes and Lophophorates

Invertebrate Phyla: Platyhelminthes and Lophophorates

Introduction and Review

• Continuing the Journey: We are continuing our exploration of invertebrate phyla.

• Recap of Covered Phyla:

  • Protists: The very first group covered.

  • Porifera: First invertebrate phylum.

  • Cnidarians.

  • Ctenophores.

• Study Habits: Encouraged early studying for these phyla as the material is dense, complementing other subjects like math and chemistry.

• Today's Focus: We will cover two phyla today, Platyhelminthes (flatworms) and Branchiopoda (represented by branchiopod), which align with the lab material.

From Radial to Bilateral Symmetry

• Evolutionary Transition: Today, we use flatworms (Platyhelminthes) as a launching point to understand bilaterality.

• Previous Phyla: The last two phyla (Cnidarians and Ctenophores) were radially symmetrical organisms.

  • Basic concepts apply to radial symmetry.

• Bilateral Organisms: Things change significantly with bilateral symmetry.

From Diploblastic to Triploblastic Development

• Diploblastic Organisms: Animals covered so far (Cnidarians and Ctenophores) are diploblastic, meaning they develop from 2 primary germ layers (ectoderm and endoderm).

• Triploblastic Organisms: Starting with Platyhelminthes, we transition to triploblastic organisms.

  • Mesoderm: A new cell cluster, the mesoderm, is added between the inner (endoderm) and outer (ectoderm) layers.

  • Increased Complexity: The presence of a mesoderm leads to:

    • More complexity in body structure.

    • Evolution of more organ systems.

    • Greater specialization of tissues and organs.

Phylum Platyhelminthes: The Flatworms

• Etymology: The name "Platyhelminthes" derives from:

  • Platy: From the Greek root for "plate" or "flat".

  • Helminth: The scientific (Latin) term for "worm".

  • Thus, Platyhelminthes means "flatworms".

• Major Groups of Flatworms: We will focus on 4 main groups:

  • Turbellaria: The