This document summarizes the key characteristics of invertebrate animals. It notes that invertebrates lack a spinal column or internal skeleton. Their body coverings vary, including hard shells, exoskeletons, and soft bodies. The document then describes several major invertebrate groups - mollusks, jellyfish, sponges, echinoderms, arthropods, and annelids - focusing on their defining physical traits. Within arthropods, it distinguishes insects, arachnids, crustaceans, and myriapods. Finally, it outlines three mollusk groups: bivalves, gastropods, and cephalopods.