What are Sponges? 

• About: Sponges are simple, aquatic animals belonging to the phylum Porifera. They are among the oldest and most primitive multicellular organisms on Earth, with a fossil record dating back over 600 million years. 
• Key Characteristics of Sponges: 
• No True Tissues or Organs: They lack complex body systems like nerves, muscles, or digestive tracts. 
• Filter-Feeding Mechanism: They draw in water through numerous pores (ostia) on their body surface. Specialized cells called choanocytes (collar cells) trap and ingest bacteria, plankton, and organic particles from the water, which is then expelled through larger openings called oscula. 
• Skeleton: They possess a simple skeleton made of mineral spicules (e.g., silica, calcium carbonate) and/or a fibrous protein called spongin. 
• Habitat: Mostly marine, but some species live in freshwater (like those studied in the Sundarbans). 
• Symbiotic Relationships: They host diverse microbial communities (bacteria, archaea) that play crucial roles in nutrition, chemical defense, and, as recent research shows, bioremediation. 
• Role in Mitigating Heavy Metal Pollution: Sponges show strong bioaccumulation of toxic metals such as arsenic, lead, and cadmium, concentrating them far more than the surrounding water. They remove these heavy metals through adsorption where metal ions attach to the sponge’s surface or are trapped in its porous structure.