GENERAL HISTOLOGY

Detailed explanation-1: -Echinoderms do not have brains, they have nerves running from the mouth into each arm or along the body. They have tiny eyespots at the end of each arm which only detect light or dark. Some of their tube feet, are also sensitive to chemicals and this allows them to find the source of smells, such as food.

Detailed explanation-2: -Although they may appear very different, echinoderms all have two major defining characteristics that set them apart from all other animals: a water vascular system and five-sided radial symmetry.

Detailed explanation-3: -Since echinoderms lack well developed nervous systems, it would be easy to assume they are unable to see, but a few special cases show that there are exceptions. Many sea stars and sea urchins show evidence of being able to perceive light and dark.

Detailed explanation-4: -A starfish has eyespots that cannot see much in the way of details but can detect light and dark. These eyespots are at the tip of each of the starfish’s arms. That means that a 5-armed starfish has five eyespots, and a 40-armed starfish has 40!