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