What Are Invertebrates?
Imagine this for a moment: Of all the animals found on planet earth, more than 9 out of every ten are invertebrates. An invertebrate is an animal that lacks a backbone or spine. This simply means that the majority of the animals that are living between the deepest oceans and the tallest mountains are invertebrates. Invertebrates, like all other living things, act as very important members of the food web. They help the environment in many ways, such as controlling the population of other insect pests or by helping with the pollination of plants. Pollination is the process by which pollen is passed from one part of a plant flower to another part of a plant flower. The entire animal world would be at risk of starvation if all invertebrates disappeared overnight.
There are many different types of invertebrates. Invertebrates include sponges, Echinoderms, Cnidarians, Molluscs, segmented worms and Arthropods.
Sponges are the most basic of all invertebrates. Most sponges live in salt water and obtain food through the movement of water through their bodies. Sponges do not usually move around on their own; they can be found attached to the surfaces of other objects in the water, such as coral and rocks. When water passes through their bodies, nutrients and other minerals, mostly from plankton, are absorbed by the sponge to satisfy the sponge’s basic energy requirement.
Echinoderms are radially symmetrical. That means that from the center, no matter the direction that you turn, Echinoderms will be equal. Examples of Echinoderms include starfish, sea urchins, sea lilies, sea cucumbers, etc. Echinoderms can be easily identified through their spiny or prickly outer coating. This protective armor acts as a great defense against some predators.
Cnidarians are radially symmetrical sea creatures that have tentacles encircling their mouths. Some Cnidarians, such as jelly fish, have soft bodies and long, stinging, poisonous tentacles that they use to immobilize their prey before eating them. Other examples of Cnidarians include coral, sea anemones, and hydras.
Molluscs are the second largest group of invertebrate animals behind arthropods. Their bodies are not divided into segments. They have antennae, or tentacles, and no true legs. Molluscs include, but are not limited to, snails, octopus, and slugs. Molluscs all have soft bodies; however, some molluscs have a hard outer shell for security. Removal of the shells will uncover a soft bodied creature. Molluscs have been an important part of the human diet for thousands of years. Also, the shells of molluscs have been traditionally used for tools and jewelry. Due to their large numbers, molluscs can also be a bother depending on the environment in which they inhabit. For example, some molluscs are regarded as non-insect pests because of the amount of damage they can do to crops by feeding on the leaves, usually at night when it is damp and cool.
Segmented worms are invertebrates that do not possess legs or a hard outer coating. Highlighting a difference with molluscs, segmented worms, also called annelids, are divided into many little segments, like rings joined together. There are three main groups of annelids: earthworms, leeches and polychaetes.
Arthropods are the largest and most diverse group of invertebrates. Arthropods can be found in a wide range of ecosystems (oceans, freshwater bodies, deserts and even rainforests). Arthropods have jointed legs, a hard outer coating called an exoskeleton and a segmented body. Due to the fact that most arthropods’ bodies are covered with an exoskeleton, they periodically go through a process called molting to rid themselves of their now outgrown exoskeletons. This exoskeleton acts as a protective shield against other organisms and from the environment in which they live. This prevents their bodies from drying out and protects them from being another organism’s next meal.
Arthropods can be divided into two main groups, those with three (3) legs (insects) and those with more than three (3) legs. Examples of Arthropods include insects, centipedes, millipedes, spiders, mites, horseshoe crabs, scorpions and crustaceans. Arthropods are probably the most feared category of invertebrates around. Thus, the mere mention of their names will send shivers through the spines of entomophobes and arachnophobes. An entomophobe is a person who is afraid of insects, while an arachnophobe is a person who is scared of spiders.
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