Invertebrates first appeared between 543 and 488 million years ago based on fossil evidence, though some appeared possibly as early as 1 billion years ago. They lacked a vertebral column and included animals with shells as well as 97% of all animal species today such as insects, crabs, lobsters, snails, octopuses and starfish. The term invertebrate is derived from the Latin word for joint and means without vertebra or spinal column.

1. WHEN DID INVERTEBRATES APPEAR?
Invertebrates appeared between 543 and 488 million years ago. They were so;-body
animals with a shell. However, there are 665 million year old fossils in the Western
Central Flinders, Australia. Some
paleontologists say that these
animals appeared much earlier,
possibly 1 billion years ago. They
have no vertebral column.
Some examples are insects, crabs,
lobsters, snails, octopuses, starfish,
sea-urchins and earthworms.
About the 97% of all animals are
invertebrates.
The word “invertebrate” comes
from the laPn word vertebra, that
means joint. Vertebra is derived
from verto, another word in laPn which comes from the concept of turning. It also
contains the prefix –in which means “without”. So, completely, the word
“invertebrate” means “no vertebra”.
The largest group of invertebrates are insects (arthropods) which appeared between
410 and 400 million years ago, around 100 million years more than the appearance of
invertebrates. There are exactly 1,305,075 insect species.