The crustacean heart ultrastructure and its bearing upon the position of the isopods in eumalacostracan phylogeny

The present paper discusses the use of myocardial ultrastructure, and its merits, in studies of crustacean phylogeny. It is argued that different modifications of the heart do not affect the membrane systems of the myofibers and that the membrane systems are independent of size and/or adaptation of the species. Finally, the phylogenetic implications of the membrane systems are considered. Using the myocardial membrane systems in addition to the cephalothorax (carapace), compound eyes, respiratory system and heart anatomy, a new phylogenetic arrangement of the larger eumalacostracan orders (Anaspidacea, Amphipoda, Cumacea, Decapoda, Euphausiacea, Isopoda, Mysidacea, Tanaidacea) is suggested. The isopods are regarded as a sister group to the other eumalacostracans.