Which of the following is NOT characteristic of the phylum Echinodermata?

In the context of the phylum Echinodermata, the correct answer highlights a key aspect of these organisms. Echinoderms, which include sea stars, sea urchins, and sea cucumbers, are exclusively marine animals, thriving in oceanic environments. They are known for their radial symmetry, particularly as adults, which allows for a symmetrical arrangement of body parts around a central axis. The presence of a water vascular system is a defining feature of this phylum, facilitating movement and feeding through hydraulic pressure.

The statement that Echinoderms are exclusively freshwater is incorrect because this phylum does not include species that inhabit freshwater environments; they are adapted to marine habitats. Thus, the assertion that they only occupy freshwater environments is in direct contrast to the established knowledge of Echinodermata, making it the correct choice for the question.