Phylogeny of basal descendants of cocoon-forming annelids (Clitellata)

Molecular analyses have been unsuccessful in placing the clitellates among annelids. Available morphological characters are ordered into congruent transformation series according to Hennigian principles. Orbiniidae is chosen as the outgroup. I propose the following phylogeny [number of apomorphies within brackets]: (Clitellata sensu lato [6] (Questidae [6] + Apodadrilida, new [2] (Parergodrilidae [3] (Stygocapitella [3] + Parergodrilus [4]) + Oligochaeta [7] (Aphanoneura [2] (Aeolosomatidae [2] + Potamodrilidae [3]) + Dorsopharyngea, new [7] (Hrabeiellidae, new [6] + Euclitellata [5])))). Worms with ring-like clitella surrounding the body almost completely are herein renamed Euclitellata. Clitellata is expanded to include all annelids that, in addition to producing cocoons, have sperm receptacles and a restricted number of gonads. Oligochaeta is established as a valid clade for the hermaphroditic annelids bearing few or no chaetae. Questidae, Parergodrilidae, and Hrabeiella belong to Clitellata. Terrestrial "polychaetes", such as Parergodrilus and Hrabeiella, are actually clitellates. Hrabeiella is the sister group of Euclitellata, despite a secondary loss of spermathecae and clitellum. Aphanoneura belong to Oligochaeta.