The Schizoramia hypothesis suffers on several grounds. The Arachnomorpha hypothesis has been questioned as a plausible basis for classifying trilobites (Scholtz and Edgecombe, 2005), though even if trilobites are instead allied to mandibulates, other ‘‘arachnomorphs’’with biramous appendages may still be stem group chelicerates (e.g., if megacheiran ‘‘great appendage’’arthro- pods like Haikoucaris are stem group Chelicerata; Chen et al. 2004; Cotton and Braddy, 2004). More problematic is the fact that biramy itself has come under serious fire as a homology between crusta- ceans and any chelicerate-allied taxa or stem group arthropods. The clonal analyses of crustacean limbs by Wolff and Scholtz (2008) suggest that ‘‘biramy ’’inCrustacea is uniquely produced by split- ting of a single developmental axis, such that the exopod of crus- taceans would not be homologous with the outer branch of fossil ‘‘biramous limbs’’,which is instead an exite possibly homologous with an epipodite.