Body Segmentation

With the exception of spiders and mites, most arthropods have clearly segmented bodies, at least ventrally on the abdomen (or opisthosoma).  Even beetles, which may look smooth and featureless dorsally have clear abdominal segments ventrally.  Segmentation is obscure in some soft-bodied insects and in ostracods it is not apparent.

Allow Misinterpretations:  Some armored mites appear to be segmented and are included here as misinterpretations.  These tend to be among the smallest of the Acari (e.g. Tarsonemidae, Pygmephoroidea, Enarthronota) and are usually <0.5 mm long.  The 'segments' are dorsal only: no ventral segments are present.