The anatomy of the pharynx of two predatory aquatic oligochaetes

Abstract

The genera Haplotaxis (Haplotaxidae) and Phagodrilus (Lumbriculidae) have convergent modifications of the pharynx that are adaptations for ingesting prey, especially other oligochaetes. Neither these taxa nor the predatory lumbriculid Agriodrilus (which is not closely related to Phagodrilus within that family) need be considered to be directly related to the leeches or branchiobdellidans simply because of these modifications. The commensal and predatory life style has evolved quite independently in several oligochaetes. Haplotaxis does not have a furrow across the prostomium as previously described. The prostomium consists of a very short bulb on the end of a peristomium, which is elongate dorsally and divided by the first obvious external transverse groove. In the Oligochaeta the peristomium is considered by convention to be segment I, but in the Polychaeta segment numbers begin with the first setiger (regarded as II in Oligochaea). In leeches the prostomium is counted as I.