Rucete ✏ Campbell Biology In a Nutshell
Unit 5 THE EVOLUTIONARY HISTORY OF BIOLOGICAL DIVERSITY — Concept 33.1 Sponges Are Basal Animals That Lack Tissues
Sponges, or Porifera, are simple, sessile animals that represent the most ancient lineage in the animal kingdom. Unlike most animals, they lack true tissues, but their unique cellular organization and filter-feeding strategy make them highly efficient and ecologically important.
Basic Characteristics of Sponges
- Belong to Phylum Porifera, commonly known as sponges.
- Basal animals—diverged early from all other animals.
- Mostly marine, but some live in freshwater.
- Body resembles a perforated sac for water flow.
- Two body layers with gelatinous mesohyl in between.
- No true tissues or organs, but have specialized cells.
Filter Feeding Mechanism
- Filter feeders: draw water in, trap food particles.
- Water enters through pores, passes through the spongocoel, and exits via the osculum.
- Choanocytes (collar cells):
- Line the spongocoel.
- Use flagella to generate water flow and capture food by phagocytosis.
- Structurally similar to choanoflagellates, linking them evolutionarily.
- Amoebocytes:
- Mobile cells in the mesohyl.
- Distribute nutrients, digest food, and form skeletal fibers (spicules or spongin).
- Totipotent: can become other sponge cell types.
Sponge Structure and Flexibility
- Some have spicules (silica or calcium carbonate) for support.
- Others have a spongin skeleton—more flexible.
- Body structure is flexible and responsive to environmental changes.
Reproduction
- Most are hermaphrodites:
- Produce both sperm and eggs, usually not simultaneously.
- Fertilization occurs when sperm enter another sponge and fertilize internal eggs.
- Larvae are flagellated and motile, allowing dispersal.
Medical and Ecological Importance
- Produce bioactive compounds:
- Includes antibiotics and anticancer agents.
- Example: Cribrostatin—kills cancer cells and drug-resistant bacteria.
- Play vital roles in:
- Filtering water
- Recycling nutrients
- Providing habitats for marine life
In a Nutshell
Sponges are the most ancient and structurally simple animals, lacking tissues but using specialized cells like choanocytes and amoebocytes for feeding and maintenance. Their unique body plan, filter-feeding, and potential for biomedical applications highlight their evolutionary and ecological importance.