recap

32.2 recap

Adult echinoderms are characterized by pentaradial symmetry, an internal skeleton of calcified plates, and a unique water vascular system. Hemichordates have a bilaterally symmetrical body divided into three parts: proboscis, collar, and trunk. Both groups are restricted to marine environments.

learning outcomes

You should be able to:

  • Compare the body plans of larval and adult echinoderms.

  • Summarize the ways that various echinoderms use their tube feet to feed.

  • Contrast the ways that echinoderms and hemichordates feed.

Question 1

How does the body form of echinoderm larvae differ from that of echinoderm adults?

Echinoderm larvae have bilateral symmetry, whereas the adults have pentaradial symmetry.

Question 2

Describe some of the ways that echinoderms use their tube feet to obtain food, and contrast this with the feeding mechanism of hemichordates.

Sea lilies and sea urchins use their mucus-covered tube feet to filter-feed by catching passing food particles, including phytoplankton. Sea cucumbers have anterior tube feet that are modified into large, sticky tentacles that can be protruded from the mouth to capture food, then withdrawn to wipe the food into the mouth. Many sea stars use their tube feet to grasp and pull open bivalves, then push their stomach into the bivalves to digest them. Like some echinoderms, hemichordates are filter-feeders, but they lack tube feet. Instead, they capture their food on a large, mucus-covered proboscis and then move the mucus and food by cilia into the mouth.

Having described the deuterostome groups that are most distantly related to us, we will next turn our attention to the unique features that evolved in the chordates, a clade dominated by the vertebrates.