An invertebrate animal is an animal that does not have an internal skeleton or a backbone. There are lots of invertebrates in the world.
The main groups of invertebrates are: sponges, molluscs, annelids, cnidarians, arthropods and echinoderms.
Most invertebrates are oviparous however, some can reproduce by budding or fission.
Sponges are animals that live in water. They fix themselves to rocks and other submerged objects. Most sponges live in the sea. They have irregular shaped bodies with canals. They feed on the nutrients in the water that goes through their canals. Humans use sponges (both real and sinthetic), you can find them in most houses in the bathrooms.
Cnidarians are animals with radial symmetry. All cnidarians are aquatic and most of them live in the sea. Sea anemones, corals and jellyfish are cnidarians.
Echinoderms are animals that live at the bottom of the sea. Starfish and sea urchins are echinoderms.
Annelids are also called worms. They are invertebrates with long, soft bodies, they do not have feet and move by wriggling. They have moist skin and live in the sea, fresh water or damp soil.
Molluscs have got soft and moist bodies. Most of them live in the water although some, like land snails and slugs, live on land. Molluscs are classified into gastropods, cephalopods and bivalves.
Arthropods have an external exoskeleton divided into different jointed parts. There are more arthropods on the planet than any other type of animal and can be classified into four different groups: crustaceans, arachnids, myriapods and insects.
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