Answer:
Echinoderms have an internal skeleton.
Explanation:
Echinoderms are the mostly marine animals and they are also known as spiny hedgehog. The adults show radially symmetry and shows indirect development.
The echinoderms shows some unique characteristics with the other members of the phylum. They have well developed water vascular system. The skeleton is internal in echinoderms and especially made of the calcium carbonate.
Thus, the answer is they have an internal skeleton.
