Final answer:
Starfish are the echinoderms described in the question with 5 to 50 arms. Other types of echinoderms like sea urchins, sea cucumbers, and sea lilies do not have such a broad range of arm numbers.
Step-by-step explanation:
The echinoderms described in the question as having anywhere from 5 to 50 arms are Starfish (A). Echinoderms are a diverse group of marine animals, and starfish vary widely in terms of size, habitat, and number of arms. While most people think of starfish as having five arms, there are indeed species with many more.
Sea urchins (B), Sea cucumbers (C), and Sea lilies (D) are other types of echinoderms, but they do not possess such a wide range of arms if any at all. Sea urchins usually have a globular shape with spines instead of arms. Sea cucumbers have leathery bodies with tentacles around their mouths, and sea lilies, although possessing feathery arms for feeding, are not known to have as many as 50 arms like some starfish can.