from Brian W.J. Mahy writing in The Biology of Paramyxoviruses:
There is no abstract for this chapter, however the first paragraph is presented here instead. The chapters in this excellent book provide a truly comprehensive account of all known paramyxoviruses, a group whose members include highly pathogenic viruses affecting the human population, as well as animals and birds. In the early days of virology, the word "myxovirus" was coined for a group of viruses that had common features, namely an affinity for mucoproteins, and an enzyme activity that attacks the mucoprotein substrate (Andrewes et al, 1955). This group of viruses included fowl plague, first discovered in 1901 (Centanni, 1901), and later shown to be a highly virulent form of avian influenza virus (Davenport et al, 1960), as well as the human viruses, influenza, para-influenza, mumps, and avian Newcastle disease virus. Soon after this group was named, however, a number of biological differences as well as structural differences were noted between influenza and fowl plague viruses, on the one hand, and para-influenza, mumps and Newcastle disease viruses on the other (Andrewes and Worthington, 1959; Franklin and Wecker, 1959). This led to the concept of two kinds of myxovirus (Waterson, 1962), now known as the families Orthomyxoviridae and Paramyxoviridae. With hindsight, we now know that orthomyxoviruses are totally different in their structure and replication from paramyxoviruses, and their only features in common are the properties of binding to mucoproteins by a virion envelope protein and release by a receptor destroying enzyme, the neuraminidase, as originally recognized (Andrewes et al, 1955). The orthomyxovirus genome consists of negative-stranded RNA which is segmented, and transcription of this genome occurs within the nucleus and requires capped oligonucleotide primer RNAs (10-13 nucleotides long) that are derived from newly synthesized host cell mRNAs by endonuclease activity of the virus PB2 protein. Because of this intimate involvement with host cell transcription, orthomyxovirus replication is blocked by substances such as actinomycin D or alpha-amanitin, which do not affect paramyxovirus replication.
Further reading: The Biology of Paramyxoviruses