Collar cells are found in which of the following? 

The correct answer is Sponges.

Key Points

• Collar cells, also known as choanocytes, are specialized cells found exclusively in sponges (Phylum Porifera).
• These cells have a flagellum surrounded by a collar-like structure composed of microvilli, which helps in water circulation and nutrient capture.
• Choanocytes line the internal chambers of sponges, particularly the spongocoel or canals, facilitating filter feeding by trapping food particles from water.
• The beating of the flagella in collar cells generates a current, ensuring water flow through the sponge's body for respiration, excretion, and feeding.
• Collar cells are a critical feature that distinguishes sponges from other animals, reflecting their evolutionary significance.

Additional Information

• Sponges (Phylum Porifera):
  • Sponges are simple, multicellular, and sessile animals primarily found in marine environments.
  • They have a porous body structure and lack tissues, organs, and a nervous system.
  • Sponges rely on water flow for essential life processes such as feeding, respiration, and waste removal.
• Filter Feeding:
  • Filter feeding is a method of nutrient acquisition where organisms extract small food particles from water.
  • Sponges use choanocytes to filter bacteria, plankton, and organic matter from the water.
• Types of Sponge Canal Systems:
  • Asconoid: Simplest canal system with a single spongocoel.
  • Syconoid: More complex with folded canals.
  • Leuconoid: Most complex, with a network of chambers and canals.
• Evolutionary Significance of Sponges:
  • Sponges are considered one of the earliest multicellular animals, providing insights into the evolution of multicellularity.
  • Their simple body organization and unique feeding mechanism make them key organisms in understanding animal phylogeny.