 The order Phthiraptera is clearly a monophyletic grouping , united as the members are by a number of derived features including their parasitism on warm @-@ blooded vertebrates and the combination of their metathoracic ganglia with their abdominal ganglia to form a single ventral nerve junction . The order has traditionally been divided into two suborders , the sucking lice ( Anoplura ) and the chewing ( Mallophaga ) ; however , recent classifications suggest that the Mallophaga are paraphyletic and four suborders are now recognized : 
