Uniramia, the largest subphylum of phylum Arthropods includes myriapods and insects. Due to the unbranched nature of the appendages of its members, the subphylum is designated Uniramia, as against those of crustaceans and primitive chelicerates which are branched and hence biramous. The uniramians have mandibles that are non-jointed, unbranched appendages without any palps; there have just only a single pair of antennae which correspond to the second cephalic segment (second antennae). Uniramians comprising taken to terrestrial mode of life, have developed trachea as gas exchanging organs; hence the subphylum is also termed as Tracheata. Malpighian tubules are the excretory organs. Uniramia involves over a million species of arthropods, of which nearly a million species are insects. About 10,500 species belong to four other classes Chilopoda, Diplopoda, Pauropoda and Symplyla. These latter four groups are collectively termed as myriapods arthropods.