|MadSci Network: General Biology|
I will focus my answer on arachnids. I'm less familar with insects and myriapods. The circulatory system of spiders is very different from that of mammals. In mammals the circulatory system is closed. Arteries branch but end within the tissues. Spider blood is called hemolymph. Hemolymph is a clear sticky liquid with a blue-green tint. There are four kinds of cells that make up this hemolymph and the one that is most like our white blood cells is called hemocytes. These cells behave very similar to lymphocytes in mammals, forming antibodies to fight infection. Hemocyanin does the work of the red blood cells but it is not contained in cells but flows throughout the hemolymph. I hope this helps! Elizabeth Mule' Schultz, S. and Schultz, M (1998) The Tarantula Keepers Guide. Barrons: NY The Spider: http://www .xs4all.nl/~ednieuw/Spiders/InfoNed/blood.html
Try the links in the MadSci Library for more information on General Biology.