Sponges
Jessica Harwood
Douglas Wilkin, Ph.D.
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AUTHORS
Jessica Harwood
Douglas Wilkin, Ph.D.
EDITOR
Douglas Wilkin, Ph.D.
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Printed: January 4, 2016
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C HAPTER
Chapter 1. Sponges
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Sponges
• Describe the key features of sponges.
• Summarize feeding in sponges.
Do animals wash your dishes?
Natural sponges, like the one in the picture above, are actually animals taken from the sea! The sponges in your
home, however, were most likely never living things. Most sponges used in kitchens today are made from unnatural
materials.
Sponges
Sponges ( Figure 1.1) are classified in the phylum Porifera, from the Latin words meaning "having pores." These
pores allow the movement of water into the sponges’ sac-like bodies. Sponges must pump water through their bodies
in order to eat. Because sponges are sessile, meaning they cannot move, they filter water to obtain their food. They
are, therefore, known as filter feeders. Filter feeders must filter the water to separate out the organisms and nutrients
they want to eat from those they do not.
You might think that sponges don’t look like animals at all. They don’t have a head or legs. Internally, they do not
have brains, stomachs, or other organs. This is because sponges evolved much earlier than other animals. In fact,
sponges do not even have true tissues. Instead, their bodies are made up of specialized cells (cell-level organization)
that do specific jobs. Other animals, including humans, have tissue-level organization because they have tissues with
specific functions.
Sponge cells perform a variety of bodily functions and appear to be more independent of each other than are the
cells of other animals. For example, some cells control the flow of water, in and out of the sponge, by increasing or
decreasing the size of the pores.
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FIGURE 1.1
The sponges often have tube-like bodies
with many tiny pores. There are roughly
5,000 sponge species.
Sponges are characterized by a feeding system unique among animals. As sponges don’t have mouths, they must
feed by some other method. Sponges have tiny pores in their outer walls through which water is drawn. Cells in
the sponge walls filter food from the water as the water is pumped through the body and out other larger openings.
The flow of water through the sponge is unidirectional, driven by the beating of flagella, which line the surface of
chambers connected by a series of canals.
Sponges reproduce by both asexual and sexual means. Sponges that reproduce asexually produce buds or, more
often, structures called gemmules, which are packets of several cells of various types inside a protective covering.
Freshwater sponges often produce gemmules prior to winter, which then develop into adult sponges beginning the
following spring. Most sponges that reproduce sexually are hermaphroditic and produce eggs and sperm at different
times. Sperm are frequently released into the water, where they are captured by sponges of the same species. The
sperm are then transported to eggs, fertilization occurs and the zygotes develop into larvae. Some sponges release
their larvae, where others retain them for some time. Once the larvae are in the water, they settle and develop into
juvenile sponges.
Summary
• Sponges are sessile filter feeders.
• Sponges lack true tissues.
Explore More
Use the resource below to answer the questions that follow.
• Sponges: Origins at http://vimeo.com/37032195 (14:02)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/57285
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5.
Chapter 1. Sponges
How do sponge cells work together?
How do most sponges feed? Explain your answer as fully as possible.
Where do sponges take in water? Where do they expel water?
What evidence do scientists point to when they say sponges may be the oldest type of animal on the planet?
What is the "heart" of sponges that controls circulation?
Review
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2.
3.
4.
What is a sea sponge?
How do sponges gain nutrition?
What is meant by cell-level organization?
Define sessile.
References
1. Image copyright Dennis Sabo, 2014. Sea sponges often have tube-like bodies with many tiny pores . Used
under license from Shutterstock.com
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