GENERAL HISTOLOGY

Detailed explanation-1: -Forms of echinoderms from the past and now are the exact same. These look more like plants than animals, and they existed most abundantly during the Cambrian period of earth’s history.

Detailed explanation-2: -The correct answer is (b). Echinoderms do not have gills.

Detailed explanation-3: -Echinoderms have spiny skin. Unio is a mollusc. So, the correct answer is option D.

Detailed explanation-4: -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. The water vascular system is a complex series of canals running through an echinoderm’s body (Fig. 3.84).

Detailed explanation-5: -Echinoderms evolved from animals with bilateral symmetry. Although adult echinoderms possess pentaradial symmetry, their larvae are ciliated, free-swimming organisms with bilateral symmetry. Later, during metamorphosis, the left side of the body grows at the expense of the right side, which is eventually absorbed.