NEET BIOLOGY

Detailed explanation-1: -Within the echinoderms, sea urchins are classified as echinoids (class Echinoidea). Specifically, the term “sea urchin” refers to the “regular echinoids, ” which are symmetrical and globular.

Detailed explanation-2: -“Regular” sea urchins show radial symmetry with a little flattened globe-like body. The anus lies on the “north pole” or in the center of the aboral surface whereas the mouth lies on the “south pole” or in the center of the oral surface that faces the substrate.

Detailed explanation-3: -Spherical Symmetry. The body has the shape of a sphere and the parts are arranged concentrically around or radiate from the center of the sphere. Such an animal has no ends or sides, and any plane. It is found mainly in Protozoa(e.g., Volvox, Heliozoa, and Radiolaria).

Detailed explanation-4: -Examples of echinoderms include sea stars, sea urchins, sea cucumbers, brittle stars, and feather stars (Fig. 3.83). 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-5: -Abstract. Bilaterally symmetrical, “regular” sea urchins in the Family Echinometridae (Class Echinoidea; Phylum Echinodermata) were found to lack a locomotor anterior.