Potergites senectus was a minute eucnemid false click beetle whose body was engineered around protected, tightly folded appendages. Grooves along the prothorax, metasternum and abdomen received the antennae and tarsi, while the pronotum ended in sharp rear angles and the elytra carried fine longitudinal striae. No head is known from the type series, so the feeding structures of the adult remain unobserved.

The larval biology of living Eucnemidae provides the best ecological guide. Most develop inside rotten, fungus-decayed wood, and many appear to exploit fungal tissues or fluids rather than sound timber itself. A saproxylic, fungus-associated larval life is therefore a well-supported inference for P. senectus, although neither a host tree nor a particular fungus can be assigned. The London Clay material is dominated by pyritised thoraces and hindbodies, with elytra preserved in only part of the series.