Updates knowledge of the ultrastructure and phylogeny of spermatozoa of the invertebrates. Much new information is included on the sperm of non-chelicerate arthropod groups: the Decapoda, Pentastomida and Myriapoda and also the Lophophorata, and the unequivocally deuterostome groups, Echinodermata, Chordata, Urochordata, and Chephalochordata. It is part of the ninth volume in the series: Progress in Male Gamete Ultrastructure and Phylogeny.