Sponge Feeding Architecture: Ostia, Canals & Nutrient Absorption

Sponges (Porifera) are sessile filter feeders. Their body wall is perforated by countless ostia (incurrent pores) leading to a complex canal system.

Water Flow Path

1. Ostia → incurrent canals → prosopyles → flagellated chamber (choanocyte chamber) → apopyles → excurrent canals → osculum (excurrent opening).

Choanocytes (Collar Cells)

• Line the flagellated chamber.
• Flagellum beats → creates inward current.
• Collar (microvilli) traps bacteria, detritus (<0.5–50 µm).
• Phagocytosis → intracellular digestion; nutrients transferred to archaeocytes (amoebocytes) for distribution.

Adaptive Significance

• High surface‑area‑to‑volume via canal system.
• Continuous flow without muscular pump.
• Particle size selection by ostia/prosopyles dimensions.

Body Plans

• Asconoid: simple tube (few ostia → spongocoel → osculum)
• Syconoid: folded wall → radial canals
• Leuconoid: complex, many small chambers (most sponges) – maximal filtration.