Any animal that lacks a vertebral column, or backbone.
They include the annelids , cnidarians , echinoderms , flatworms , nematodes , mollusks , and arthropods . More than 90% of living animals are invertebrates. Worldwide in distribution, they range in size from minute protozoans to giant squids. Apart from the absence of a vertebral column, invertebrates have little in common. They are generally soft-bodied and have an external skeleton for muscle attachment and protection. See also {{link=vertebrate">vertebrate .