GENERAL HISTOLOGY

Detailed explanation-1: -Sand dollars-flattened sea urchins adapted to life on the shifting sand-use thousands of tiny spines to move about and burrow into the seafloor.

Detailed explanation-2: -The endoskeletal structure of the Sea Urchin, Centrostephanus rodgersii, has numerous long spines whose known functions include locomotion, sensing, and protection against predators. These spines have a remarkable internal microstructure and are made of single-crystal calcite.

Detailed explanation-3: -Sea urchins and sand dollars (Echinoidea) are a group of echinoderms that are spiny, globe or disk-shaped animals. Sea urchins and sand dollars are found in all the world’s oceans. Like most other echinoderms, they are pentaradially symmetrical (the have five sides arranged around a central point).

Detailed explanation-4: -Most sea stars, though not all, have five arms. Sea urchins have five arms but roll them into a ball and cover that with long spines. Sand dollars are just sea urchins that have been flattened like a pancake and have very short spines. Echinoderms can regenerate body parts.