A taxonomic group within the animal kingdom, comprising marine species characterized by a hard, spiny covering or skin. This category encompasses a diverse range of organisms including starfish, sea urchins, and sea cucumbers. The group also associates with other animal subcategories such as mollusks, which include bivalves and squid, and amphibians. These creatures all fall under the broad umbrella of animal life, sharing common characteristics and processes despite their varied forms and habitats.