Final answer:
The flagellated cells in sponges responsible for water circulation and feeding are called choanocytes, or 'collar cells'. They use a flagellum to move water and a collar to trap food particles, which they then ingest by phagocytosis.
Step-by-step explanation:
The flagellated cells that line the internal cavity of a sponge and help water flow through the Ostia are called choanocytes, or 'collar cells'. These cells are critical for the sponge's ability to filter feed by generating a directed water current and trapping microscopic food particles for ingestion.
Choanocytes contain a mesh-like collar composed of microvilli surrounding a central flagellum. As the flagella of the choanocytes beat, they draw water into the sponge through the ostia and out through the osculum.
The collar efficiently traps food particles, which are then ingested by the choanocyte through phagocytosis. These specialized cells also contribute to the sexual reproduction in sponges, as they can differentiate into sperm when needed. Choanocytes exemplify a simple but efficient feeding mechanism in these primitive multicellular organisms.
These cells have a collar-like structure with a single flagellum in the center, surrounded by microvilli. The beating of the flagella from the choanocytes creates a water current that draws water into the sponge through the ostia and eventually out through the osculum.