Category Animal World

               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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               There is so much diversity among invertebrates. This diversity prevents classifying them under a single over-arching category. Scientists have identified more than 30 phyla of invertebrates. Since vertebrates have a single identifying factor called vertebra, it is not difficult to classify them. However, invertebrates are any other animals classified outside of that class. Let us look at some of them in detail.

               A wide variety of interesting ocean animals that are invertebrates includes sponges, corals, jellyfish, anemones, and starfish.

               Molluscs, another category of invertebrates, have a soft body that is covered by an outer layer called a mantle. Many molluscs live inside a shell, but not all of them. Some examples of molluscs include squid, snails, slugs, octopuses, and oysters.

               Crustaceans are a type of arthropod. Arthropods are characterized by jointed legs. They also have an exoskeleton, meaning that their bones are on the outside like a shell. Some examples of crustaceans are crabs, lobster, shrimp, and barnacles.

              Worms are invertebrate animals that do not have legs. Worms may live in the soil, in the water, or even inside other animals as parasites. Some examples include the tapeworm, the leech, and the earthworm.

              Insects are part of the earth’s largest animal phylum, the arthropods. There are over 1 million species of insects including the grasshopper, dragonfly, yellow jacket, butterfly and praying mantis.

              Spiders, centipedes and scorpions are all part of the arthropod phylum. Spiders and scorpions are arachnids because they have eight legs. Centipedes and millipedes are myriapods and have many legs. Some myriapods have as many as 750 legs. Some example species include the tarantula and black widow, which are both spiders.

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            Most invertebrates that we are familiar with are very small. We often associate the smallness of an ant, a caterpillar, or a grass-hopper with insignificance. Therefore, we have no remorse when such small insects die. However, invertebrates play a very important role in the eco-system.

            As invertebrates are generally small, they can hide in places where larger animals cannot catch them. Therefore, their size is an advantage when it comes to protecting themselves. In spite of their small size, these animals play a key role in maintaining the balance of nature.

            Invertebrates play various roles in nature. Those that are herbivores keep plants and trees in check. Some invertebrates are carnivores, eating other invertebrates as well as larger animals, to prevent the overpopulation of some species. Others are parasites, keeping the number of a certain type of plant or animal under control. Perhaps most important of all, some invertebrates eat dead animal and plant matter. This releases important nutrients back into the environment so that other plants and animals can use them again.

            Most invertebrates also provide food for other species of animals, and even for carnivorous plants like the sundew. Therefore, though most invertebrates are small, they are far more important to the ecosystem than all the mammals, birds, reptiles, amphibians and fish put together.

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              Which is more intelligent: a dog or a mosquito? You will not think twice to answer the question. Bigger animals tend to be smarter and more intelligent. However, does their skeletal system have anything to do with their intelligence?

              It is not wise to generalize about smartness and intelligence when it comes to invertebrates. They are diverse in size and form. There are hardly any similarities among species as different as enormous moths, ethereal medusas, skittering scorpions, or stationary sponges. However, there is no need for any debate on this: the lack of a backbone may mean they are ‘spineless’, however, that does not mean that all of them are mindless!

              Cephalopods, squid and octopus in particular, are some of the most intelligent invertebrates. They are capable of learning quickly and retaining information. Spiders learn to weave better webs through trial and error. Honeybees learn to recognize their hives. At the same time, curiously enough, starfish and sponges do very well with no brains at all!

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               Can you observe some of the animals around you? It would be interesting note that most big animals such as a cow, a dog or a cat have strong internal skeletal structure. Now look at some small organisms such as a butterfly, a beetle or an earthworm. They do not possess an internal bone system. Does size have anything to do with such differences?

               Most invertebrates are small because they lack internal skeletons. An external skeleton is an inhibitor and makes it difficult for an animal to grow further. If it grows too big, it will not fit inside the skeleton. If the skeleton grew bigger to accommodate the animal’s increasing size, it would become too heavy for the animal to carry.

               However, it would be wrong to assume that all invertebrates are small. Invertebrates that live in the sea can grow quite big. There are giant clams in the South Pacific that are 1.2 metres across, and weigh a quarter of a tonne! Giant squids can reach a length of 17 metres, and weigh a tonne!

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            Those animals with backbones have a much more developed skeletal structure and tend to be stronger than invertebrates. Therefore, invertebrates have to look for other means to protect themselves from danger.

           Many invertebrates have strong shells that substitute for a backbone. These external structures play an important role in their survival. The shells protect the invertebrates from predators. They also prevent their bodies from drying up when they are out of water.

          Other invertebrates have developed various ways to defend themselves. Some brightly coloured sea slugs taste so terrible that other animals do not want to eat them. Sea anemones possess numerous stinging tentacles, and sharp spines shield the sea urchins body. These are just some of the ways by which invertebrates survive.

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