GENERAL HISTOLOGY

Detailed explanation-1: -Starfish are the best known echinoderm group. Starfish usually have five arms, but sometimes more, radiating from a central disk. The ossicles of the body wall are rodlike and articulate via fibrous junctions to form a flexible grid. Respiration is by the tube feet and skin gills.

Detailed explanation-2: -The phylum echinoderms is divided into five extant classes: Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins and sand dollars), Crinoidea (sea lilies or feather stars), and Holothuroidea (sea cucumbers). The most well-known echinoderms are members of class Asteroidea, or sea stars.

Detailed explanation-3: -Sea stars are invertebrates related to sea urchins, sea cucumbers and sand dollars, which are all echinoderms. Echinoderm means spiny skin-a reference to their hard, calcified skin, which helps to protect them from predators. Sea stars have rows of tiny tube feet extending from the grooved surface on their underside.

Detailed explanation-4: -One characteristic of an echinoderm is that they all have pentamerous radial symmetry. This simply means they all have 5 equal body parts. You can divide these animals into five equal parts, and every part is the same. For example, most sea stars have five arms or a multiple of five arms.