Tetramerocerata is an order of pauropods containing 11 families and more than 900 species.[1] This order was created in 1950 to distinguish these pauropods from those in the newly discovered genus Millotauropus, which was found to have such distinctive features as to warrant placement in a separate order (Hexamerocerata) created to contain that genus. The order Tetramerocerata includes the vast majority of pauropod species, as there are only eight species in the order Hexamerocerata, which remains the only other order in the class Pauropoda.[2]
Adult pauropods in the order Tetramerocerata feature antennae that have four stalk segments and are not telescopic, whereas species in the order Hexamerocerata have strongly telescopic antennae with six stalk segments.[3] Adults in the order Tetramerocerata also have trunks with six tergites that may be entire or divided, whereas those in the order Hexamerocerata have twelve entire tergites. Most adults in the order Tetramerocerata have nine leg pairs,[4] but those in four genera (Cauvetauropus, Aletopauropus, Zygopauropus, and Amphipauropus) have only eight pairs, and adult females in the genus Decapauropus (in the Pauropodidae family) have either nine or ten pairs of legs.[5] Adults in the order Hexamerocerata, however, have eleven leg pairs.
Most species in the order Tetramerocerata develop through a series of five post-embryonic stages, from the first instar to the adult. Juveniles in this order begin with three pairs of legs, seven trunk segments, and three tergites, then in most species in this order, they become adults with nine leg pairs, twelve trunk segments, and six tergites. Pauropods in this order have three leg pairs in the first stage, then five pairs in the second, six pairs in the third, eight pairs in the fourth, and for most species in this order, nine pairs in the fifth (adult) stage. Juveniles in the order Hexamerocerata, however, begin with six leg pairs, nine trunk segments, and eight tergites, then become adults with eleven leg pairs, eleven trunk segments, and twelve tergites, going through stages with six, eight, nine, ten, and eleven leg pairs.
Tetramerocerata has a subcosmopolitan distribution, with species found nearly worldwide.
This order includes the following families: