Answer:
The correct answer would be echinoderms.
Endoskeleton refers to the skeletal system found inside the body of an organism.
It is mainly found in organisms belonging to Chordata, Echinodermata, Coleoidea, and Porifera.
Echinoderms were among the first animals to develop endoskeleton.
They have a mesodermal skeleton which is primarily composed of calcareous ossicles or plates
Both of the structures are composed of crystals of calcite which form a porous structure termed as stereom.