Perionychini Jamieson, 1971

Perionychini Jamieson, 1971 .

The tribe Perionychini (defined by megascolecin male pores and holonephridia, irrespective of prostate type) is represented here by five genera. There is no convincing support in any analysis for a unified or monophyletic Perionychini although there is evidence that some of these holonephric megascolecines are closely related. There is, however, much instability in perionychin relationships, reflected in low BS values and lack of consensus ( Figs 3-5 View FIG View FIG View FIG ). In all analyses the “perionychin” (acanthodrile sensu Gates) Pontodrilus diverges at or near the base of the Megascolecinae s.l., and while exclusion from the Acanthodrilinae is upheld, its uncertain placement reflects its enigmatic affinities on morphological and ecological grounds. Pontodrilus is highly unusual among crassiclitellates in being euryhaline. It may be suspected of having had a long independent evolution. The tribe Perionychini , although a convenient taxonomic grouping, is thus a para- or polyphyletic assemblage in the molecular analyses. This has previously been suspected ( Jamieson 1988) as the Perionychini is recognized on the basis of the symplesiomorphic possession of holonephridia (a condition seen throughout the Oligochaeta, whereas meronephry is virtually limited to Megascolecidae ). It is therefore a grade rather than a clade.