GENERAL HISTOLOGY

Detailed explanation-1: -Echinoids are marine animals belonging to the phylum Echinodermata and the class Echinoidea. They have a hard shell (referred to as a test) covered with small knobs (tubercles) to which spines are attached in living echinoids. The test and spines are the parts normally found as fossils.

Detailed explanation-2: -Spines are ossicles that project from the body wall and articulate with other ossicles through ball and socket joints mounted on tubercles. They are formed from crystals of calcite and can be solid or hollow, long or short, thick or thin and sharp or blunt.

Detailed explanation-3: -Echinoderm means spiny skin so the last characteristic they all share is…. spiny skin. The spines are very obvious in some echinoderms. The sea urchins, for example, have obvious spines covering their body.

Detailed explanation-4: -The spines of irregular echinoids are extremely miniaturized to form a dense felt which facilitates locomotion and burrowing, as well as feeding.