Invertebrates, as the name suggests have no vertebra; and therefore, most of them do not have the ability to stand erect or walk on legs. They are multi-cellular too. Their cells are working together for the survival of the organism. All of the cells have specific duties and responsibilities.
Invertebrates do not have cell walls, whereas plants have them. One of the most important characteristics of animals is that they have no cell walls. Even though no insect looks like an animal, this quality makes it an animal.
Most of them have tissues that are specific organizations of cells. Most invertebrates can move. Even sponges move when they are very young and very small. Once they settle down, they do not move anymore. Other invertebrates like lobsters and insects move around their whole lives. Most invertebrates are organized in a symmetrical way. Symmetrical organization means when you can draw a line down the middle of the organism and the two sides look like mirror images. If you draw a line down the middle of an octopus, you would find two sides with equal parts. However, sponges and some coral are not symmetrical.
Invertebrates cannot make their own food; and are, therefore, heterotrophic. Heterotrophs feed off other things to get their energy. Plants are autotrophic. They make their own food. Being heterotrophic is one of the main characteristics of being an animal.
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