Final answer:
The category that includes spiny-skinned animals like starfish and sea urchins is Echinoderms, belonging to the phylum Echinodermata.
Step-by-step explanation:
The category that includes spiny-skinned water animals like starfish and sea urchins is c) Echinoderms. These animals belong to the phylum Echinodermata, which is characterized by a distinctive spiny skin and an endoskeleton made up of calcareous ossicles. Members of this phylum are exclusively marine and possess unique features such as radial symmetry as adults, bilateral symmetry as larvae, and a water vascular system that allows for movement using tube feet. Some of the different classes of Echinodermata include Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins), Crinoidea (sea lilies), and Holothuroidea (sea cucumbers). Spiny-skinned water animals, such as starfish and sea urchins, fall under the category of Echinoderms. Echinoderms constitute a diverse phylum of marine invertebrates characterized by a unique water vascular system and a spiny or bumpy skin. These fascinating creatures inhabit oceans worldwide, exhibiting radial symmetry and a decentralized nervous system. Unlike mammals, which are warm-blooded vertebrates, or reptiles and amphibians, which belong to different animal classes, echinoderms represent a distinct group. Their evolutionary adaptations enable them to thrive in marine environments, showcasing a variety of body forms and ecological roles within ocean ecosystems.