Porifera: Water Canal System | Zoology Optional Notes for UPSC PDF Download

Canal System in Porifera (Sponges)

1. Asconoid Type:
Description:

• The simplest canal system characterized by a radially symmetrical vase-like body with a central spongocoel.
• Composed of outer and inner epithelium, mesenchyme, and perforated by incurrent pores.
• Choanocytes in the inner epithelium facilitate water current and nutrient exchange.
• Water Current Route:
  • From exterior through incurrent pores to spongocoel and out through the osculum.
• Examples: Olynthus, Leucosolenia.

2. Syconoid Type:
Description:

• Evolves from the asconoid type through the formation of radial canals, later developing incurrent canals.
• Choanocyte-lined radial canals and epidermis-lined incurrent canals characterize this stage.
• Internal ostia, prosopyles, and osculum mark the path of water flow.
• Water Current Route:
  • Dermal pores to osculum through incurrent canals, radial canals, and spongocoel.
• Examples: Sycon (first stage), heterocoelous calcareous sponges.

3. Leuconoid Type:
Description:

• Develops from syconoid through further out folding, resulting in small flagellated chambers.
• Choanocytes confined to these chambers, mesenchyme filling the intervening space.
• Complex network of incurrent and excurrent canals.
• Water Current Route:
  • Dermal pores to oscula through incurrent canals, flagellated chambers, and excurrent canals.
• Variations: Eurypylous, aphodal, diplodal.

4. Rhagon Type:
Description:

• Unique to demospongiae, arising from direct rearrangement of inner cell mass.
• Conical shape with a single osculum, devoid of flagellated chambers at the base.
• Flagellated chambers lead into spongocoel through incurrent canals.
• Water Current Route:
  • Ostia to osculum through incurrent canals, flagellated chambers, and excurrent canals.

Functions of Canal System

• The canal system facilitates these vital functions by ensuring a continuous flow of water.
• It transports nutrients, oxygen, and carries away metabolic wastes.
• Enables the transfer of sperm between sponges for fertilization.
• Increases surface area and volume, maintaining a fixed ratio.

In summary, the canal system in porifera plays a crucial role in their physiological processes and contributes to their diverse forms and functionalities.