These viruses were historically placed into three groups, polioviruses, coxsackieviruses, and echoviruses, all on the basis of criteria which we would now find trivial. The group coxsackievirus was named because these viruses were pathogenic for infant mice and because the first virus of this type was isolated from a patient from the town of Coxsackie New York. The echovirus group on the other had was named for another reason. These viruses were not found to be pathogenic for infant mice, and were thus considered to be "orphan," since they caused no apparent disease, and were first isolated in cell culture from the feces of asymptomatic people. The echo in echovirus actually stands for enteric cytopathogenic human orphan viruses. However we now know that echoviruses do cause apparent infection, so this criteria for classification is invalid.
Because this classification system was such a mess, it was stopped some time ago. Since 1970 any new enterovirus that has been isolated has simply been given an enterovirus number starting with enterovirus 68. In addition to this, three viruses that were originally classified in the Enterovirus genus have been reclassified somewhere else, and recently the case has been made for the reclassification of echoviruses 22 and 23 within a new genus of the Picornaviridae family.