Lecture 3: Porifera and Cnidaria

Overview

This lecture focuses on the phyla Porifera and Cnidaria, covering their characteristics, classification, life cycles, and ecological roles.

Porifera (Sponges)

• Characteristics
  • Simplest multicellular animals
  • Lack true tissues and organs
  • Body structure includes pores (ostia), central cavity (spongocoel), and exit opening (osculum)
  • Skeletal elements: spicules and spongin
• Classification
  • Three main classes: Calcarea, Hexactinellida, Demospongiae
• Reproduction
  • Asexual reproduction through budding and fragmentation
  • Sexual reproduction with internal fertilization
• Ecological Role
  • Filter feeders, play a role in water filtration
  • Provide habitat for marine organisms

Cnidaria

• Characteristics
  • Radial symmetry, diploblastic (two tissue layers)
  • Possess cnidocytes with nematocysts (stinging cells)
  • Two main body forms: polyp and medusa
• Classification
  • Four main classes: Hydrozoa, Scyphozoa, Cubozoa, Anthozoa
• Life Cycle
  • Includes both polyp and medusa stages (varies among classes)
  • Example: Jellyfish life cycle involves alternation between polyp and medusa forms
• Ecological Role
  • Predators and prey in marine ecosystems
  • Reef-building corals (Anthozoa) are crucial for marine biodiversity

Key Comparisons

• Porifera vs Cnidaria
  • Porifera: no true tissues, sessile, filter feeders
  • Cnidaria: have tissues, may be sessile or mobile, use cnidocytes for prey capture

Summary

• Porifera and Cnidaria represent simple multicellular life forms with unique adaptations.
• Understanding their biology and ecology is crucial for marine biodiversity and conservation efforts.