This document provides an overview of invertebrates. It defines invertebrates as animals without backbones and internal skeletons. The document outlines several phyla of invertebrates including porifera, cnidaria, and worms. Key characteristics of each phylum are described, such as porifera having pores and spicules, cnidaria having stinging cells, and worms having segmented or unsegmented bodies. The objectives are to explain invertebrates, discuss their characteristics, name the phyla, describe each phyla, and classify common invertebrates.