Canal Systems Encountered in Different Sponges
The arrangement and complexity of internal channels vary considerably in
different sponges. Accordingly, the canal system has been divided into following
types- Ascon, Sycon, Leucon and Rhagon.
1. Asconoid Type:
The asconoid type of canal system is regarded to be the most simple and
primitive grade of canal system. Asconoid type is present in these sponges
whose body is vase-like and radially symmetrical. The wall is extremely thin. It
encloses a large spongocoel opening at the summit by a narrow osculum. The
spongocoel is lined by choanocytes. The wall is pierced by numerous
microscopic apertures termed as the incurrent pores or ostia which extend from
the external surface to the spongocoel. Each pore is intracellular disposed in a
porocyte. The asconoid type of canal system is characterised by the presence of
a complete continuous layer of choanocytes lining the spongocoel interrupted
only by the porocyte.
Occurrence:
This type of canal system is found in some simple adult calareous sponges (eg.,
Leucosolenia, Clathrina). It also occurs in Olynthus stage of some newly settled
calcareous sponges (e.g., Clathrina).
Physiology of water current production:
Constant water current is created by the beating of the flagella of choanocytes.
The flagella do not beat synchronously, but beat independently. The water
current passes directly through the ostia into the spongocoel and goes out
through an apical opening, the osculum.
Course of water:
, 2. Syconoid Type:
The syconoid type of canal system represents the transitional grade between
the simplest ascon type and more complex ones. The first step above the
asconoid type of canal system is represented by the syconoid type of canal
system. The complication is due to the out-pushing of the wall into finger-like
projections, called the radial canals, at regular intervals. In type of canal system,
choanocytes are only limited to the radial canals. Their detailed account has
already been described with the biology of Sycon.
The syconoid canal system Is represented by two grades:
(i) Simple sycon type
(ii) Complex sycon type and
I) Simple sycon type:
The simple type of canal system is found in the heterocoelous calcareous
sponges typified by Sycetta. The radial canals are free projections of the wall
without touching at any point and the external surface is composed of the blind
outer ends of the radial canals.
The incurrent canals have not definitely formed and the spaces between the
radial canals serve as the dermal ostia. The radial tube is lined by flagellated
cells but the Spongocoel is lined by flattened pinacocyte cells.
Course of water:
II) Complex sycon type:
The complex sycon type canal system is found in Grantia, Heteropia, Scypha and
there is an opposition. The walls of the adjacent radial canals are arranged in
The arrangement and complexity of internal channels vary considerably in
different sponges. Accordingly, the canal system has been divided into following
types- Ascon, Sycon, Leucon and Rhagon.
1. Asconoid Type:
The asconoid type of canal system is regarded to be the most simple and
primitive grade of canal system. Asconoid type is present in these sponges
whose body is vase-like and radially symmetrical. The wall is extremely thin. It
encloses a large spongocoel opening at the summit by a narrow osculum. The
spongocoel is lined by choanocytes. The wall is pierced by numerous
microscopic apertures termed as the incurrent pores or ostia which extend from
the external surface to the spongocoel. Each pore is intracellular disposed in a
porocyte. The asconoid type of canal system is characterised by the presence of
a complete continuous layer of choanocytes lining the spongocoel interrupted
only by the porocyte.
Occurrence:
This type of canal system is found in some simple adult calareous sponges (eg.,
Leucosolenia, Clathrina). It also occurs in Olynthus stage of some newly settled
calcareous sponges (e.g., Clathrina).
Physiology of water current production:
Constant water current is created by the beating of the flagella of choanocytes.
The flagella do not beat synchronously, but beat independently. The water
current passes directly through the ostia into the spongocoel and goes out
through an apical opening, the osculum.
Course of water:
, 2. Syconoid Type:
The syconoid type of canal system represents the transitional grade between
the simplest ascon type and more complex ones. The first step above the
asconoid type of canal system is represented by the syconoid type of canal
system. The complication is due to the out-pushing of the wall into finger-like
projections, called the radial canals, at regular intervals. In type of canal system,
choanocytes are only limited to the radial canals. Their detailed account has
already been described with the biology of Sycon.
The syconoid canal system Is represented by two grades:
(i) Simple sycon type
(ii) Complex sycon type and
I) Simple sycon type:
The simple type of canal system is found in the heterocoelous calcareous
sponges typified by Sycetta. The radial canals are free projections of the wall
without touching at any point and the external surface is composed of the blind
outer ends of the radial canals.
The incurrent canals have not definitely formed and the spaces between the
radial canals serve as the dermal ostia. The radial tube is lined by flagellated
cells but the Spongocoel is lined by flattened pinacocyte cells.
Course of water:
II) Complex sycon type:
The complex sycon type canal system is found in Grantia, Heteropia, Scypha and
there is an opposition. The walls of the adjacent radial canals are arranged in
