GENERAL HISTOLOGY

Detailed explanation-1: -sea urchin, any of about 950 living species of spiny marine invertebrate animals (class Echinoidea, phylum Echinodermata) with a globular body and a radial arrangement of organs, shown by five bands of pores running from mouth to anus over the test (internal skeleton).

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: -Echinoderms feed on a variety of marine life in a variety of ways. Filter feeders, like brittle stars, absorb nutrients in marine water. Suspension feeders use their arms to capture floating food particles. Grazers, like sea urchins, feed on both plants and animals, making them omnivores.

Detailed explanation-4: -Sea urchins are spherical, oval or flattened free-moving echinoderms covered with spines. Their soft tissue anatomy is characterized by a dominant digestive tract, a varying number of gonads, and the highly specialized water vascular system with its external appendages, the tube or ambulacral feet.