How can the endoskeleton of echinoderms be characterized in comparison to analogous structures present in vertebrates, arthropods and molluscs?
The echinoderm skeleton is internal, i.e., it is an endoskeleton. It is made of calcium carbonate (calcareous). Vertebrates also have internal skeleton made of bones and cartilages. Arthropods have an external carapace made of chitin, a chitinous exoskeleton. Some molluscs present a calcareous shell that works as exoskeleton.
