Animal Database
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Animal Database

A species of cephalopod

Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a backbone or spine), derived from the notochord. This includes all animals apart from the chordate subphylum Vertebrata. Familiar examples of invertebrates include arthropods (insects, arachnids, crustaceans, and myriapods), mollusks (chitons, snails, bivalves, squids, and octopuses), annelid (earthworms and leeches), and cnidarians (hydras, jellyfishes, sea anemones, and corals).

The majority of animal species are invertebrates; one estimate puts the figure at 97%. Many invertebrate taxa have a greater number and variety of species than the entire subphylum of Vertebrata. Invertebrates vary widely in size, from 50 μm (0.002 in) rotifers to the 9–10 m (30–33 ft) colossal squid.

Some so-called invertebrates, such as the Tunicata and Cephalochordata, are more closely related to vertebrates than to other invertebrates. This makes the invertebrates paraphyletic, so the term has little meaning in taxonomy.

Phyla Examples Image Estimated number of

described species

Arthropoda Insects, Spiders, Scorpions, Centipedes, Crabs, Shrimps

A wasp

1,170,000
Mollusca Octopuses, Squids, Oysters, Clams, Snails

A Common Nautilus

85,000
Annelida Earthworms, Ragworms, Leeches

A Blood Worm

22,000
Platyhelminthes Flatworms, Flukes, Tapeworms

New Zealand Flatworm

20,000
Nematodes Roundworms

Roundworm

Rotifera Wheel Animals

A Rotifer

Porifera Sponges

A sponge

Cnidaria Jellyfish, Sea fans, Corals, Sea Anemone

A Pacific Sea Nettle

~11,000
Echinodermata Starfish, Brittle Stars, Sea Urchins

A starfish

~7000
Ctenophora Comb Jellies

A Comb Jelly

~150
Onychophora Velvet Worms

A velvet worm

165
~1,300,000 Total:
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