Both are grouped under Schizoramia, a clade of arthropods with biramous appendages. The appendages of arthropods may be either biramous or uniramous. This arrangement suggests the animals are related to biramous arthropods. The antennae are branching, biramous, and segmented, which is distinctive for the group. Parapodia are mostly biramous (only the first two pairs are uniramous). Trilobites, for instance, also possessed biramous appendages. These are biramous (branched) and bear filamentous gills. The first pair of antennae are slender, black or dark brown and biramous. The second pair of antennae, however, is long and biramous. However, whether the ancestral limb was uniramous or biramous is far from a settled debate. Crustacean limbs also differ in being biramous, whereas all other extant arthropods have uniramous limbs. The second antennae are plesiomorphically biramous, but many species later evolved uniramous pairs. In both sexes, the uropods are biramous. This pair is generally uniramous, but is biramous in crabs and lobsters and remipedes. The pleopods are biramous, except in Sicyoniidae, where they are uniramous.