Points to Consider
- What do you think that jellyfishes and corals have in common?
- Think of some examples of animals that are bilaterally symmetrical, where the left side
is a mirror image of the right?
11.2 Lesson 11.2: Sponges and Cnidarians
Lesson Objectives
- Describe the key features of the Sponges.
- Describe the key features of the Cnidarians.
- List examples of the Cnidarians.
Check Your Understanding
- How are animals classified?
- What is an invertebrate?
Introduction
The ocean is home to a variety of organisms. Phytoplankton, tiny photosynthetic organisms
that float in the water, make their own food from the energy of the sun. Small aquatic
animals, known as zooplankton, and larger animals, such as fish, use phytoplankton as a
food source. These animals can in turn be eaten by larger aquatic animals, such as larger
fish and sharks.
Among the various types of animals that live in the ocean, thespongesandcnidariansare
important invertebrates. The Sponges are believed to be one of the most ancient forms of
animal life on earth. The cnidarians, which include the jellyfish, also are among the oldest
and most unusual animals on earth. In this lesson we will discuss the features that make
these two types of invertebrates unique from other types of animals.
Sponges
Sponges are classified in the phylumPorifera, which derives its name from Latin words
meaning “pore bearing.” These pores allow the movement of water into the sponges’ sac-like
bodies (Figure11.5). Sponges pump water through their bodies because they aresessile
filter feeders, meaning they cannot move and must filter organic matter and tiny organisms
out of the water to obtain food.