Category Animal World

               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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              What, do you think, would happen if we had no backbone? Our backbone not only supports our body, but also enables us to walk erectly. Without a backbone, vertebrates in general would not be able to survive in nature.

              However, as we have already seen, not all animals have backbones. Then, how do they survive? Internal and external skeletons help an animal to survive without a backbone. Some invertebrates have internal skeletons that support and protect their internal tissues. These skeletons are made up of different materials. Sponges have a framework of silica or other substances that stiffen their bodies. Others have external skeletons in the form of shells. Invertebrates belonging to the molluscs group have shells made of calcium carbonate, while those that are anthropods have external skeletons made up of a substance called chitin.

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              Have you seen the picture of the skeleton of a man? A strong backbone system supports our body. Man is able to stand erect or walk because of his backbone. Invertebrates are animals without a backbone. Of the millions of species of animals on the planet, 97 per cent are invertebrates. Common examples of invertebrates include snails, clams, insects, spiders, worms and molluscs.

              Do you think that all animals on Earth have the same body structure? Do insects such as caterpillars and bees have backbones like mammals such as bears and sloths? Even though they are all animals, insects and mammals have very different body structures! Caterpillars and bees are invertebrates.

              In the animal kingdom, invertebrates are actually the largest group. They make up 97 per cent of all animals on the planet. The total number of invertebrate species could be over 30 million. This number is much higher than that of the vertebrates, which is about 60,000. Invertebrates are also very diverse. They include animals living on the land and those living in the sea. Some examples are earthworms, centipedes, flies, sea stars, jellyfish and crawfish!

             Invertebrates have a long history of existence on Earth. Fossil records show that invertebrates even existed 600 million years ago. Invertebrates also have a big impact on other animals’ lives. They are a major food source for other animal species such as birds and fish. In agricultural production, some of them act as pests and parasites. This includes bugs like grasshoppers and ladybugs.

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              Classifying animals into groups was based entirely on observation initially. Our observation has a limited scope because we rely exclusively on our senses, which can sometimes deceive us. However, today, with modern equipment with more precision and accuracy, Man is able to do this job better.

              Animal classification now uses sophisticated scientific methods to identify relationships among species. Since the methods used to classify animals are continuously changing, there is the probability that the groups in which species are placed may change too. Occasionally, new species are identified!

               For example, until recently, elephants were classified into two species: African and Asian elephants. But DNA studies conducted in 2010 revealed that African elephants actually are of two distinct species- African bush elephants and African forest elephants. This, there are three species of elephants in the world now!

                                                                                                               

              Do you know that all the animals that we know have separate scientific names? Sometimes, it is very difficult to recall these names too. However knowledge of their scientific names would help us categorize animals according to their similarities and differences.

              The system of naming that we follow today is called the binomial system. It is the formal method of naming different species. Under the binomial system, each species is given a scientific name that is formed by the combination of two terms: the genus name and the specific descriptor.

              The genus is the major subdivision into which organisms are classified. The descriptor is the category into which the organism falls. For example, the scientific name for man is ‘Homo Sapiens’. ‘Homo’ is the genus name for animals that have large brains and use tools. ‘Sapiens’ is the category that pertains to modern humans.

              Here is a list of the binomial name of some common animals: Dog – Canis lupus, Cat – Felis catus, Horse – Equus caballus, Goat – Capra aegagrus hircus, Donkey – Equus asinus, Cow- Bos Taurus, Tiger-Panthera Tigris, Lion – Felis Leo, Indian Elephant- Elephas maximus indicus.

 

 

                 From the time language originated, Man starter naming animals. His scientific temper prompted him to order and categorize all living and non-living things for easier understanding. Man observed, named and compared animals and plants.

                 Aristotle, an ancient Greek philosopher, was the first known man to introduce the classification of animals. He classified species according to various characteristics, including whether they gave birth or laid eggs, or whether they were warm or cold-blooded.

                 The Roman naturalist Pliny the Elder wrote Naturalis Historia, a large work in which many plants were described. Naturalis Historia is also considered the first encyclopedia.

 

                 Over the years, animal classification became more scientific. The 16th century Italian philosopher Andrea Cesalpino classified plants according to their fruits and seeds.

                 The English naturalist John Ray published works on botany and zoology in the 17th century. He classified species according to the similarities that he observed, and was the first person to offer a scientific definition of the word species.

                 The Swedish botanist Carl Linnaeus of 18th century is known as the father of modern taxonomy. He popularized the binomial naming system, and introduced the use of kingdoms, classes, orders, genera and species. The Linnaean system is still in use today.