Canal system in Scypha

Canal system in Scypha
Body of Scypha consists of a complex system of pores and canals. This system is generally referred to as canal system or aquiferous system. Bodywall has cellular layers, outer pinacoderm and inner choanoderm. In between these two layers, there is a non-cellular gelatinous mesenchyme in between. But the bodywall is so folded as to form regularly arranged alternating invaginations and evaginations, establishing the sycon type of canal system. The various components of canal system of Scypha are:
1) Ostia or dermal pores
2) Incurrent canals
3) Prosopyles
4) Radial canals
5) Apopyles
6) Spongocoel
7) Osculum
8) Current of water

1) Ostia or dermal pores:
The external grooves of body surface are stretched over by a thin pore membrane. It bears two or more openings for the ingress of outside water into the body of sponge. These pores are known as Ostia (Latin, Ostium=door) or dermal pores. Because of the presence of contractile cells or myocytes around them, the ostia can reduce in diameter and thus regulate the amount of ingressing (incoming) water.
2) Incurrent canals:
These are the invaginated folds of bodywall and are also called inhalent canals. These communicate with outside through ostia but end blindly at their inner ends. Pinacocytes line these canals throughout.
3) Prosopyles:
Incurrent canals communicate with radial canals through intercellular spaces called prosopyles (Greek. Pros=near, pyle=gate)
4) Radial canals:
Evaginations of bodywall form thimble-shaped chambers lined by flagellated choanocytes. These chambers are called flagellated or radial canals.
Incurrent and radial canals are parallel and alternate with each other, both vertically and radially. The arrangement is such that, in a vertical or tangential section through the wall of a cylinder, each radial canal is surrounded on four sides by incurrent canals, and each incurrent canal is surrounded likewise by four radial canals.
Radial canals end blindly at their outer ends but lead at their inner ends into spongocoel.
5) Apopyles:
Openings of radial canals into spongocoel are called apopyles (Greek apo=away from, pyle=gate) or internal ostia. These are surrounded by contractile myocytes serving as a sphincter.
6) Spongocoel:
It is the large central cavity of the body forming the vertical axis of the cylinder (Greek sponges=sponge+koilos=hollow). In Leucosolenia, spongocoel is lined by flagellated collar cells or choanocytes. In Scypha, the choanocytes line the radial canals, whereas the spongocoel is lined with the epidermal pinacocytes.
7) Osculum:
Spongocoel leads to outside through a terminal opening, the osculum. The oscula are provided with sphincters to regulate the rate of water flow in the body. Sphincters are lined by special contractile pinacocytes.
Sphincters are lined by special contractile pinacocytes, called myocytes (Greek. Myos, muscle+kytos=cell)
8) Current of water
Flow of water in canal system is maintained by continuous beating of flagella of collar cells lining the radial canals. Every beat of a flagellum consists of a normal active stroke and a recovery stroke. Electron microscopy revealed that there is no coordination between the beating of flagella of adjacent cells. The course taken by water current into the canal system is as follows.

Water from outside through dermal ostia Incurrent canals through prosopyles


Radial canals

Through apopyles
to outside Spongocoel Radial canals