Which class includes starfish and sea urchins?

Study for the IB Marine Science Standard Level Exam. Prepare with interactive quizzes and in-depth explanations. Use our resources to excel in your marine science knowledge!

Multiple Choice

Which class includes starfish and sea urchins?

Explanation:
Starfish and sea urchins are both echinoderms, but they belong to different classes. Starfish are in the class Asteroidea, which features a central disc with usually five radiating arms and tube feet operated by a water vascular system that they use for locomotion and feeding. Sea urchins are in the class Echinoidea, which has a rigid, plate-covered skeleton (test) with movable spines and no arms. So there isn’t a single class that includes both; recognizing the distinct classes shows how body plans differentiate even within the same phylum.

Starfish and sea urchins are both echinoderms, but they belong to different classes. Starfish are in the class Asteroidea, which features a central disc with usually five radiating arms and tube feet operated by a water vascular system that they use for locomotion and feeding. Sea urchins are in the class Echinoidea, which has a rigid, plate-covered skeleton (test) with movable spines and no arms. So there isn’t a single class that includes both; recognizing the distinct classes shows how body plans differentiate even within the same phylum.

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