Six general questions:

1
Six general questions
How are they classified? What do they look
like? How do they support themselves and
locomote? How do they feed and digest? How do
they maintain homeostasis? How do they reproduce
and develop?
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Phylum Porifera
Parazoan - no true embryonic tissues Cells are
totipotent - they change form and function and
they are mobile throughout the body.
Approximately 9000 species encrusting and
upright marine, intertidal, freshwater
A group of sponges is a sleeze.
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Phylum Porifera
Class Calcarea
Spicules composed of calcium carbonate. Exclusivel
y marine. Considered the most primitive of
sponges. Color usually dull.
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Phylum Porifera
Class Hexactinellida
Glass sponges Siliceous, six-rayed spicules of
hydrated SiO2. Exclusively marine, found in deep
water.
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Phylum Porifera
Class Demospongiae
Siliceous spicules or organic collagen
network. Marine and freshwater. Occur at all
depths.
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What do sponges look like?
Aquiferous system
Water is pumped through the sponge such that O2
and nutrients are brought in and CO2 and wastes
are removed.
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What do sponges look like?
Body structure
Layers of cells with specific functions. Contribut
e to aquiferous system, food uptake, and
support. Mesohyl - noncellular mesoglea which
contains spicules and many types of ameboid cells.
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What do sponges look like?
Body structure
Pinacoderm - made of pinacocytes. Outer layer
perforated with small holes where water enters.
Pinacocytes are flattened and overlapping.
Epithelial function and are probably phagocytic.
Osmoregulation in freshwater sponges.
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What do sponges look like?
Body structure
Pores are called dermal pores if they are
composed of more than on cell. Called ostia if
they are composed of only one cell.
Cells are called porocytes - cylindrical and
contractile.
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What do sponges look like?
Body structure
Choanoderm made of choanocytes - inner surface of
flagellated cells that create water currents.
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What do sponges look like?
Body types - Asconoid
Small and simple vase shape. Pinacoderm and
choanoderm are simple sheets. Porocytes are
tube-shaped cells that form ostia on pinacoderm
side and open into spongocoel on choanoderm
side. Found in all juvenile and some adult
calcareous sponges.
Water flow ostia ---gt porocyte ---gtspongocoel
---gt osculum
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What do sponges look like?
Body types - Syconoid
Various degrees of infolding to create
flagellated chambers containing chanocytes.
Mesohyl thickened. Incurrent opening is a dermal
pore surrounded by several porocytes. A system
of canals leads to the flagellated chambers. The
opening into the chamber is the
prosopyle. Chambers open to the spongocoel via a
wide opening called an apopyle. Found in many
calcareous sponges.
Water flow dermal pore ---gt incurrent canal
---gtprosopyle ---gt flagellated chamber ---gt
apopyle ---gt spongocoel ---gt osculum
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What do sponges look like?
Body types - Leuconoid
Further infolding of pinacoderm and choanoderm to
create flagellated chambers that are discreet
chambers. Spongocoel is a series of excurrent (or
exhalent) canals. Flagellated chambers have large
surface area compared to incurrent and excurrent
canal systems. Decreases water velocity to
maximize gas and nutrient exchange. Typical of
most calcareous and all demosponges.
Water flow dermal pore ---gt incurrent canal
---gtprosopyle ---gt flagellated chamber ---gt
apopyle ---gt excurrent canal ---gt osculum
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What do sponges look like?
Body types - Hexactinellid sponges
No pinacoderm. Dermal membrane with no discreet
cell structure and simple holes for
pores. Cellular material forms a trabecular
network with internal cavities called subdermal
lacunae Flagellated chambers are thimble-shaped
and supported by the trabecular network.
Prosopyles bring water from the lacunae to the
chambers. Choanocyte chambers and the trabecular
network are syncitial-there are no discrete cells)
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How do sponges support themselves?
Collagen
Secreted by collencytes, lophocytes, and
spongocytes.
Lophocytes are motile and have a band of collagen
behind them. With collencytes they secrete thin
intercellular collagen.
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How do sponges support themselves?
Spicules
Made of CaCO3 or SiO2
Occur in mesohyl. Often used for identification.
Produced by sclerocytes. Collect Ca or Si and
deposit it. Can work alone or in groups (often
two cells per spicule ray).
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How do sponges support themselves?
Spicules
Megascleres and microscleres. Calcareous sponges
have only megascleres. Demosponges and
hexactinellid sponges have both.
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How do sponges feed?
Phagocytosis and pinocytosis for intracellular
digestion
Dermal pores allow 50 mm particles. Motile
archeocytes capture small particles (2-5 mm) in
lining of inhalent canals. Digestion in food
vacuole.
Water driven through collar of chaonocytes where
other particles trapped. Food partially digested
by choanocytes then passed on to archeocytes.
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How do sponges reproduce and develop?
Asexual reproduction
Fragmentation - small bits break off and form a
new sponge Budding - new sponges grow attached
to an older sponge and eventually form a new
sponge.
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How do sponges reproduce and develop?
Sexual reproduction
Most sequential hermaphrodites. Some
gonochoristic. Most sponges release egg and sperm
into water. Fertilization external.
In some sponges, eggs produced by choanocytes or
archaeocytes and are kept in the mesohyl. Sperm
produced from spermatic cyst. Sperm travel to
other sponge, taken up by choanocyte (but not
digested) and transferred to egg. Zygote may
spend time in maternal sponge.
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How do sponges reproduce and develop?
Sexual reproduction
Holoblastic cleavage into a coeloblastula
Larvae are motile (swim and creep) and
lecithotrophic
Larvae are released by maternal sponge
coeloblastula or larval stages. Demosponges
usually incubate embryos to the parenchymula
stage.
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How do sponges reproduce and develop?
Calcareous sponges