Labels:text | screenshot | font OCR: CAMBRIAN PERIOD 570-505 MYA The first time division of the Paleozoic Era is the Cambrian Period. During this time the seas were inhabited by groups of invertebrates ( animals without a backbone) that still exist today. They include arthropods (animals without a backbone, with a jointed body case), and mollusks (soft-bodied animals without a backbone, protected by a hard shell).
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