Phylum Porifera - Sponges
• Mostly marine, but include some freshwater inhabitants;
usually found attached to the substratum in shallow or
deep water.
• They are sessile; permanently attached to the substrate
• Obtain their food by filter feeding
General Morphology
• The internal cavity is called the atrium or spongocoel
• Water is drawn into it through a series of incurrent pores or dermal
ostia present in the body wall into a central cavity and then flows out of
the sponge through a large opening at the top called the osculum
Body layers
1. The pinacoderm - an outer layer of flattened
cells called pinacocytes
2. An inner lining containing flagellated cells
(choanocytes) - draw water in through the pores
and move out through the osculum; also trap
food particles that are suspended in the water.
• The water current is also used for gas
exchange, removal of wastes, and release of the
gametes
3. Between the pinacodern and the choanocytes
is a gelatinous material called mesohyl; contains
several different kinds of wandering cells called
amoeboid cells
Archaeocytes are amoeboid cells that
phagocytize food particles; they can also
undergo differentiation to form other cells,
including cells that produce spicules and gametes
The Skeleton
In the mesohyl is the skeleton composed of tiny pointed structures
made of silica or calcium carbonate called spicules.
These structures act as an internal scaffolding, but also function in
protection
Among some sponges the skeleton consist of spongin fibers made of
collagenous material; found in many of the commercial sponges
Types of Sponges (Canal
Systems)
A. Asconoid Sponges
• Simple vaselike structure
• This stucture puts limitations on size;
(increase in volume without a
corresponding increase in the surface area
of the choanocytes)
Types of Sponges (Canal Systems)
cont.
B. Synconoid Sponges
• The flagellated choanocyte layer
has undergone folding forming
finger like projections
• There is a single osculum but
the body wall is more complex,
with water being received
through incurrent canals, which
pass it along to radial canals
through to the spongocoel
• Results in an increase in the
surface area which allowed
sponges to increase in the size
Types of Sponges (Canal Systems)
cont.
C. Leuconoid Sponges
• No atrium; several small
chambers in which choanocytes
are located
• There is a whole series of
incurrent canals leading to the
choanocyte chambers; water is
discharges through excurrent
canals
• The leuconoid sponges exhibit a
significant increase in surface
area and are, therefore, among the
largest sponges
Sponge Reproduction
• Most are hermaphroditic or monoecious.
• Sperm leaves a sponge via the osculum, and enters a sponge by the currents
generated from the choanocytes.
Fertilized eggs develop into ciliated free-swimming larvae called
parenchymula larvae
• Sponges can reproduce asexually by fragmentation
• Many of the freshwater sponges
can produce asexual bodies called
gemmules, aggregations of cells
that are enclosed in hard outer
covering containing spicules
Sponge Taxonomy
Class Calcarea
(Calcispongidae)
• Only sponges that possess
spicules composed of calcium
carbonate.
• Spicules are straight or have
3-4 rays, and do not have
hollow axial canals.
• Today, their diversity is
greatest in the tropics,
predominantly in shallow
waters
Taxonomy cont.
Class Hexactinellida
(Hyalospongiae)
• Glass sponges; characterized
by siliceous spicules consisting
of six rays intersecting at right
angles
• Widely viewed as an early
branch within the Porifera
Taxonomy cont.
Class Demospongiae
• Greater than 90 percent of the
5,000 known living sponge
species are demosponges.
• Demosponge skeletons are
composed of spongin fibers
and/or siliceous spicules
• Siliceous spicules with one to
four rays not at right angles,
All members express the
leuconoid body form
Yellow sponge growing on a wall
on a Caribbean reef.