Lecture on Animal Phyla: Porifera and Cnidaria

Introduction

• Previous Lecture Recap: Discussed basic animal characteristics, life cycles, and characteristics. Important to review these before proceeding.
• Current Focus: Phylum of invertebrates, specifically Porifera (sponges) and Cnidaria (jellyfish, sea anemones, and hydra).

Phylum Porifera

Overview

• Common Name: Sponges
• Characteristics:
  • Invertebrates
  • Asymmetrical
  • Sedentary (non-motile)
  • Micro-filter feeders
  • Indicators of environmental health
• Structure: Lack true tissues, cellular level of organization, part of the metazoans.

Body Plan

• Terminology:
  • Epidermis: Outer cell layer
  • Ostia: Openings/pores for water entry
  • Spongocoel: Central cavity
  • Osculum: Opening at the top for water exit
  • Choanocytes: Collar cells responsible for feeding
  • Amoebocytes: Totipotent cells responsible for various functions
  • Spicules: Structural elements made of silica or calcium carbonate
  • Mesohyl: Gelatinous matrix, acts as a glue

Water Flow and Feeding

• Water enters through Ostia, passes through spongocoel, and exits via osculum.
• Feeding: Choanocytes capture food particles, amoebocytes transport nutrients.

Body Forms

• Asconoid: Simplest, direct water flow
• Syconoid: More complex, increased surface area for feeding
• Leuconoid: Most complex, maximized surface area, most efficient feeding

Reproduction

• Asexual: Budding, creating clones
• Sexual: Hermaphroditic with free-swimming larvae (planula)

Classes

• Calcarea: Simple body types, calcium carbonate spicules
• Demospongiae: Complex body types, silica spicules, includes commercial sponges
• Hexactinellida: Silica spicules with six rays

Phylum Cnidaria

Overview

• Common Types: Jellyfish, sea anemones, corals
• Characteristics:
  • Radial symmetry
  • Diploblastic (2 tissue layers)
  • Part of eumetazoans (true tissues)

Body Plans

• Polyp: Sessile, mouth/anus facing up
• Medusa: Free-swimming, mouth/anus facing down
• Gastrovascular Cavity: Central digestive compartment
• Mesoglea: Jelly-like layer between tissues

Tentacles and Feeding

• Carnivorous: Use tentacles with cnidocytes containing nematocysts (harpoon structures) for capturing prey.

Clades

• Medusozoa:

  • Includes true jellyfish and other related organisms
  • Hydrozoa: Dominant polyp stage, e.g., Hydra and Obelia
    • Hydra: Solitary, asexual budding and sexual reproduction
    • Obelia: Colonial polyp, alternates with Medusa for sexual reproduction
  • Scyphozoa: True jellyfish, dominant Medusa stage

• Anthozoa:

  • Only polyp stage
  • Includes sea anemones and corals
  • Coral reefs formed by symbiosis with algae, key to marine biodiversity

Conclusion

• Importance of reading textbook for additional details.
• Invitation to reach out with questions via email.