Figure 4

Lack of the tritocerebral appendage and early col -expression plotted on current arthropod phylogenies. A The Atelocerata concept: myriapods and insects are allied, crustaceans are basally branching mandibulates; only one evolutionary event: gain of early col-function (ecf). B The Tetraconata concept: crustaceans and insects are allied sister-groups, myriapods are basally branching mandibulates; two evolutionary events: 1) gain of ecf in the stem-mandibulate and 2) loss of ecf in crustaceans. C The Pancrustacea concept: crustaceans and insects are allied with insects representing an in-group of the crustaceans; three evolutionary events: 1) gain of ecf in stem mandibulate followed by 2) a loss in the crustacean stem and finally 3) a re-gain in the insect lineage. D Convergence. Ecf does not represent a synapomorphy of insects and myriapods but evolved two times independently. Not shown: The Myriochelata concept: chelicerates and myriapods are allied and insects and crustaceans are allied; three evolutionary events in the non-convergence scenario: 1) gain of ecf in arthropod stem followed by 2) a loss in crustaceans and 3) chelicerates; Note that in the case of convergence Myriochelata is as likely as Pancrustacea/Tetraconata (shown in D).