GENERAL HISTOLOGY

Detailed explanation-1: -Through metamorphosis, the free-swimming larvae make dramatic changes in both body parts and in symmetry. The bilateral symmetry of echinoderm larvae indicates that echinoderm ancestors also may have had bilateral symmetry, suggesting a close relationship to the chordates.

Detailed explanation-2: -Echinoderms are deuterostome invertebrate animals, phylogenetically most closely related to hemichordates and to chordates. They are exclusively marine-living, with a wide range of habitats from the deep sea to the intertidal region.

Detailed explanation-3: -Most echinoderms develop from larvae to adolescent echinoderms by direct, or indirect development. In direct development, the fertilized egg is able to enter juvenile stage without becoming a larva. The juveniles stay close to the parent, and are cared for and looked after.

Detailed explanation-4: -The echinoderms are most closely related to the chordates. These two phyla share the most recent common ancestor compared to the rest of the animal phyla.