GENERAL HISTOLOGY

Detailed explanation-1: -Sea stars, sea cucumbers, sea urchins, sand dollars, and brittle stars are all examples of echinoderms. Adult echinoderms have a calcareous endoskeleton and exhibit pentaradial symmetry, although the early larval stages of all echinoderms have bilateral symmetry.

Detailed explanation-2: -Echinoderms. Echinoderms are a phylum of marine invertebrates that include starfish, brittle stars, sea cucumbers, sea urchins, sand dollars, and crinoids. They are one of the most diverse groups of marine invertebrates and play important ecological roles from the near-shore environment to the deep seas.

Detailed explanation-3: -Echinoderms are exclusively marine organisms with spiny bodies. They have an endoskeleton rich in calcium, basically made of calcareous ossicles. Ossicles are structures embedded into the body walls. They provide rigidity and protection to the body.

Detailed explanation-4: -Organisms like tortoise and crocodile posses both exoskeleton and endoskeleton. Tortoise has an outer hard shell and a skeleton inside the body. The crocodile has a tough leathery skin/hide on the outside and then a skeleton inside the body.