Most of the animals in the world are INVERTEBRATES.  These animals do not have a spinal cord or backbone. 
Most invertebrates are oviparous, and we classify them into six main big groups: 
Porifera (sponges)
Cnidarians (jellyfish and corals)
Annelids (segmented worms)
Molluscs (with or without a shell)
Echinoderms (starfish)
Arthropods: all arthropods have jointed legs. Another fascinating characteristic that they all have in common is that their body is divided into segments, and many of which, though not all, are protected by an external skeleton or exoskeleton that is used as a shield or shell. Some arthropods bodies do not grow at the same rate as their exoskeleton, therefore making them shed it for a bigger size, a process known as molting. Arthropods include insects (6 legs, ants and butterflies), arachnids (8 legs, spiders and scorpions), crustaceans (10 legs, crabs and shrimp) and myriapods (more than 10 legs, centipedes)

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