Underside of a <i>Cancer productus</i> crab. If you every doubt that arthropods have pigment in their blood which have an open circulatory systems (blood runs free in the body without vessels), turn over a crab and if you are a little lucky, you will see the purple stain seen here left from the pigment.  They do not have hemoglobin, but sure do have hemocyanin.
<a rel="nofollow" class="external text" href="https://flickr.com/people/33466410@N00">Jerry Kirkhart</a>
CC BY 2.0
originally posted to <b><a href="//commons.wikimedia.org/wiki/Flickr" class="mw-redirect" title="Flickr">Flickr</a></b> as <a rel="nofollow" class="external text" href="https://flickr.com/photos/33466410@N00/4663997548">Hemocyanin Example</a>