Haplotaxida

The Haplotaxida are one of two orders within the annelid subclass Oligochaeta, the other being the Lumbriculida. No real common name exists, but they are simply referred to as haplotaxids.
Given that the other clitellatan annelids are embedded between and around the Haplotaxida and Lumbriculida, the traditional "Oligochaeta" are a paraphyletic assemblage. Thus, the Haplotaxida might eventually be up-ranked to subclass status within the "Clitellata" or an expanded Oligochaeta, with the present suborders advancing to order rank. The latter – though without merging the "Oligochaeta" and "Clitellata" – has been proposed time and again in the past, most prominently for the distinct "Moniligastrina."
Families.
Of the four suborders of Haplotaxida, two are minor lineages, monotypic at family level. Another one, the Tubificina, is sizeable and contains the aquaworms, while the fourth, the earthworms or Lumbricina, unites the bulk of the order's families:
Suborder Haplotaxina
Suborder Moniligastrina
Suborder Lumbricina
Suborder Tubificina