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Biology
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26-2 Sponges
Photo Credit: Fred McConnaughey/Photo Researchers, Inc.
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What is a Sponge?
What is a Sponge?
Sponges are in the phylum Porifera which means “pore-bearers.”
Sponges live their entire adult life attached to a single spot.
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What is a Sponge?
Why are sponges classified as animals?
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What is a Sponge?
Sponges are classified as animals because they are :
multicellular
heterotrophic
have no cell walls
contain a few specialized cells
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6. Form and Function in Sponges
How do sponges carry out essential functions?
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7. Form and Function in Sponges
Sponges do not have a mouth or gut, and they have no tissues or organ systems.
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8. Form and Function in Sponges
Body Plan
Sponges are asymmetrical; they have no front or back ends, no left or right sides.
Sponges carry out basic functions, such as feeding and circulation, by moving water through their bodies.
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9. Form and Function in Sponges
The body of a sponge forms a wall around a large central cavity through which water is circulated continually.
Central cavity
Sponges carry out basic functions, such as feeding and circulation, by moving water through their bodies.
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10. Form and Function in Sponges
Water flow
Osculum
Water enters through pores located in the body wall and leaves through the osculum, a large hole at the top of the sponge.
Pores
Sponges carry out basic functions, such as feeding and circulation, by moving water through their bodies.
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11. Form and Function in Sponges
Choanocyte
Choanocytes are specialized cells that use flagella to move a steady current of water through the sponge.
Pore
Sponges carry out basic functions, such as feeding and circulation, by moving water through their bodies. Choanocytes use flagella to move water through pores in the wall of the sponge and out through the osculum. As water moves through the sponge, food particles are filtered from the water, and wastes are removed from the sponge.
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12. Form and Function in Sponges
The movement of water through the sponge provides a simple mechanism for feeding, respiration, circulation, and excretion.
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13. Form and Function in Sponges
Sponges have a simple skeleton. In harder sponges, the skeleton is made of spiny spicules.
A spicule is a spike-shaped structure made of calcium carbonate or silica.
Spicule
Sponges carry out basic functions, such as feeding and circulation, by moving water through their bodies.
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14. Form and Function in Sponges
Spicules are made by archaeocytes, which are specialized cells that move around within the walls of the sponge.
Archaeocytes
Sponges carry out basic functions, such as feeding and circulation, by moving water through their bodies.
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15. Form and Function in Sponges
Feeding
Sponges are filter feeders.
As water moves through the sponge, food particles are trapped and engulfed by choanocytes that line the body cavity.
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16. Form and Function in Sponges
These particles are then digested or passed on to archaeocytes, who complete the digestive process and transport digested food throughout the sponge.
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17. Form and Function in Sponges
Respiration, Circulation, and Excretion
Sponges rely on movement of water through their bodies to carry out body functions.
Oxygen dissolved in the water diffuses into the surrounding cells.
Carbon dioxide and other wastes, such as ammonia, diffuse into the water and are carried away.
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18. Form and Function in Sponges
Response
Sponges do not have nervous systems that would allow them to respond to changes in their environment.
However, many sponges protect themselves by producing toxins that make them unpalatable or poisonous to potential predators.
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19. Form and Function in Sponges
Reproduction
Sponges can reproduce sexually or asexually.
In most sponge species, a single sponge forms both eggs and sperm by meiosis.
The eggs are fertilized inside the sponge’s body, in a process called internal fertilization.
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20. Form and Function in Sponges
Sperm are released from one sponge and are carried by water currents until they enter the pores of another sponge.
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21. Form and Function in Sponges
Archaeocytes carry the sperm to an egg.
Most sponges reproduce sexually, and many have internal fertilization.
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22. Form and Function in Sponges
After fertilization, the zygote develops into a larva. A larva is an immature stage of an organism that looks different from the adult form.
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23. Form and Function in Sponges
The larvae of sponges are motile. Water currents carry the larva until it attaches to a surface and grows into a new sponge.
New sponge
Mature sponge (2N)
Swimming larva
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24. Form and Function in Sponges
Sponges can reproduce asexually by budding or by producing gemmules.
In budding, part of a sponge breaks off of the parent sponge, settles to the sea floor, and grows into a new sponge.
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25. Form and Function in Sponges
In difficult environmental conditions, some sponges produce gemmules, which are groups of archaeocytes surrounded by a tough layer of spicules.
Gemmules can survive freezing temperatures and drought. When conditions become favorable, a gemmule grows into a new sponge.
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26. Form and Function in Sponges
Sexual reproduction involves joining haploid gametes that have been produced by meiosis.
Since the zygote contains genes from both parents, the new sponge is not genetically identical to either parent.
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27. Form and Function in Sponges
Asexual reproduction, in contrast, does not involve meiosis or the joining of haploid gametes.
Asexual reproduction produces offspring that are genetically identical to the parent.
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Ecology of Sponges
Ecology of Sponges
Sponges are important in aquatic ecology.
They provide habitats for marine animals such as snails, sea stars, and shrimp.
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Ecology of Sponges
Sponges containing photosynthetic organisms play an important role in the ecology and primary productivity of coral reefs.
The spicules of some sponges look like cross-shaped antennae.
They focus and direct incoming sunlight to cells lying below the surface of the sponge—where symbiotic organisms carry out photosynthesis.
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26-2
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26-2
In sponges, a spike-shaped structure made of chalklike calcium carbonate or glasslike silica is a(an)
spicule.
archaeocyte.
choanocyte.
epidermal cell.
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26-2
An immature stage of an organism that looks different from the adult form is a(an)
gemmule.
larva.
archaeocyte.
choanocyte.
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26-2
Specialized cells that use flagella to move water through the sponge are
gemmules.
pores.
spicules.
choanocytes.
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26-2
Sponges are
detritivores.
carnivores.
filter feeders.
herbivores.
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26-2
Sponges can reproduce
sexually only.
asexually only.
both sexually and asexually.
by metamorphosis.
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36. END OF SECTION