Question

Adult echinoderms have __________ symmetry.
A) Spherical
B) Bilateral
C) Radical
D) Biradical

Answer 1

The symmetry of an animal generally fits its lifestyle. Echinoderm phylum comprises the majority of marine and some freshwater animals. It includes starfish, sea urchins, sand dollars, and sea cucumbers.

Complete answer:
Spherical symmetry occurs in an organism if it can be cut into two identical halves through any cut that runs through the organism's center and has many symmetrical planes passing through the body. Example protozoans like Radiolaria and Heliozoa and algae-like Volvox. Bilateral symmetry is a form of symmetry in which the two opposite sides are similar. Therefore the external appearance of the left and right side are the same sagittally. Examples - flatworm, octopuses, crustaceans, insects, spiders, and vertebrates including humans.
Radial symmetry is the symmetry in which the sides exhibit regularity of parts around a central axis passing through it. It is lacking the left and right sides. Example - aquatic cnidarians, which include corals, jellyfish, and sea anemones Adult echinoderms have pentamerous radial symmetry. The bilateral symmetry of their larvae is evidence that echinoderms have evolved from the bilateral symmetrical adults. Biradial symmetry is a type of symmetry in which the organism can be divided up into equal parts but only with two planes that divide the organism. examples Comb jellies.
So, option (C) is the correct option.

Note: The body of an adult in Echinodermata is radially symmetrical which is due to the circular pattern of the body which is present in most of the Echinodermata. However, the Echinodermata larvae are not radially symmetrical but are bilaterally symmetrical. The body of echinoderms has a complete digestive system in addition to a closed circulatory system. This phenomenon is called retrograde metamorphosis.