What is an invertebrate animal?
Invertebrates are animals that don't have backbone.
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How we classify them?
How we classify them?
There are different ways of classifying invertebrate animals, but we are going to use the following one:
Invertebrates
Invertebrates
Protozoa
Protozoa
They are very small animals with no legs. We can see them only if we use a microscope.
They are single celled animals, with only one cell.
They can live in water: freshwater or saltwater (seas and oceans) and even in the soil.
Coelenterates and Sponges
Coelenterates and Sponges
All of them live in salt water. Some examples of this group are the jellyfish, the coral or the sponge.
Jellyfish are about 95% water. Their body looks like an umbrella (when they are babies they look like small flowers), and they could be transparent or translucent.
They have tentacles. They eat plankton.
Sponges are made of a lot of polyps.They eat plankton from the water using the tentacles of the polyps.
Molluscs/Mollusks
Molluscs/Mollusks
Molluscs or mollusks (both words are correct) are a group of invertebrates.
Mollusks have soft bodies.
Mollusks have no legs, though some have flexible tentacles for sensing their environment or grabbing things.
Most mollusk species grow a hard shell for protection. But others don't have any shell like squids or slugs.
Echinoderms
Echinoderms
They are invertebrates.
They can only live in saltwater.
Echinoderms have no blood they use salty water instead.
They don’t have a brain.
Echinoderms are predators.
They have an internal structure called an endoskeleton.
Examples: Starfish and sea urchins.
Flatworms
Flatworms
Flatworms are very small, almost microscopic in size.
Their bodies are flat and they have no legs.
Most of them are parasitic (they live on or in other organisms and they take their food from them).
They also live in the water.
Examples of this invertebrate group would be the platyhelminth.
Annelid worms
Annelid worms
They are usually small, but others can grow longer than an Olympic swimming pool.
Annelid worms have no legs and a round segmented body (little segments, like rings joined together.)
They live in water or wet soil.
Examples: earthworm, leech or lugworm.
Arthropods
They have hard external skeleton and jointed legs.
There are 4 types: arachnids, crustaceans, insects and myriapods.
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