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Invertebrates are cold blooded animals with no backbone. In fact, they don’t have any any bones at all! It is an astonishing fact that approximately 97 percent of all living animal species are invertebrates. According to scientists there are 1.25 million species of invertebrates They include those that live on land and water. They are soft bodied animals due to the absence of a rigid internal skeleton which helps in the attachment of muscles, but they often possess a hard outer skeleton which helps in body protection. Some of the invertebrates we are quite familiar with are butterflies, spiders, worms, snails etc.
They are the most diverse and important group of animals for a healthy ecosystem. The main reason for their large number is their ability to reproduce quickly. Some lay eggs that do not need fertilization while some produce both egg and sperm. Another reason is that they can survive in extreme climatic conditions.
Importance of Invertebrates
As mentioned above, invertebrates form the major part of animal species which shows the importance of these creatures. Let’s have a look at the various role of these tiny creatures.
- Invertebrates are key elements in food chains that support birds, fish, and many other vertebrate species. They belong to the bottom layer of the food chain which show how important it is for the sustenance of other living creatures.
- Invertebrates are important as agricultural pests and parasites as they eat pests that harm the crops.
- They play an important role in plant pollination. Bees, butterflies, beetles and other invertebrate pollinators help plants to reproduce. Absence of these pollinators means loss of access to several food products like vegetables, fruits, seeds, nuts and oils.
- Some invertebrates are an important resource to the medical field. For example, horseshoe crab blood is use to detect bacterial endotoxins which has been beneficial for cancer patients.
- The invertebrates feed on dead animals and plants, thus returning nutrients back into the soil. This helps to boost the quality of soil thereby ensuring thriving forests. Examples are Mites, millipedes, earthworms, ants, termites etc.
- Certain invertebrates like grasshoppers are consumed by human and are a valuable source of protein. Silkworms are reared for the production of raw silk through sericulture. This is a high value activity in some countries.
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Types of Invertebrates
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- Protozoans
- Annelids
- Echinoderms
- Mollusks
- Arthropods – insects, spiders, crustaceans such as shrimp, crabs, lobsters
Protozoans
These are single celled organisms which are in different shapes and sizes. Examples are amoeba, euglena and paramecium. Protozoans are either free living or parasites. They live in a wide variety of moist habitats including fresh water, marine environments and the soil. They have a relatively complex internal structure and carry out complex metabolic activities.
Annelids
Annelids are segmented worms. They have tube shaped body and a specialized digestive system. Their bodies are made up of segments that are formed by subdivisions Examples are earthworm, leech, lugworms etc. Annelids are schizocoelous with a large and well developed true coelom.
Echinoderms
These are marine invertebrates who play a vital role in the marine habitat. These organisms have hard, spiny covering or skin. They have a series of water filled canals running through their body. Examples are starfish, sea urchins, sea cucumbers etc.
Mollusks
It is the second-largest phylum of invertebrate animals. They are soft bodied and are wholly or partially covered by a calcium carbonate shell. They are a good source of food, jewelry and tools. It includes organisms like squid, clams, octopus, snails etc.
Arthropods
Arthropods make up 85 percent of invertebrates or 923,000 species. They are invertebrates with jointed legs.
There are four main groups of arthropods:
- Insects
- Arachnids
- Crustaceans
- Myriapods
Insects are the largest group of invertebrates with six legs, two antennae, and three body parts. Examples are butterflies, beetles, bees and stick insects.
Arachnids have eight legs, no antennae and two body parts. The most common ones are spiders and scorpions. Even though they are feared, they are of highly beneficial as they eat pest insects, keep insect populations down and are mostly harmless to humans.
Crustaceans are animals with ten to fourteen legs, four antennae and two body parts. Crabs, lobsters and shrimp are examples of this type of invertebrates. Apart from one, all crustaceans live underwater. A pill bug is a crustacean that lives on land.
Myriapods include millipedes, centipedes, symphylans etc. They have a single pair of antennae and their mouth lies on the underside of the head.
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Characteristics of Invertebrates
By now as you know what invertebrates are, let’s get to know about their characteristics.
- Invertebrates are cold blooded, i.e. they can’t regulate their body temperature.
- Invertebrates do not have endoskeleton, i.e. a spinal cord or a skeleton, instead, most of them possess an exoskeleton that provide support and protection.
- They can live on land, salt water and fresh water.
- Normally, these are tiny and don’t grow very large.
- Invertebrates do not possess lungs and they respire through their skin.
- They are multicellular where each cell has different responsibilities.
- They may have a complete or an incomplete digestive system.
- There are invertebrates that are carnivorous, herbivores and omnivores.
- Since they cannot produce their own food, invertebrates are heterotrophic.
- Most invertebrates reproduce sexually. They reproduce by coming together of gametes
- The body of invertebrates do not produce much internal heat.
A recent research reported an alarming decline in invertebrate biomass. Action plans are being discussed and new initiatives are underway to combat the decline.
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