Key to species of Williamsrhizoecus based on the adult female

Based on keys in Kozár and Konczné Benedicty (2007) and Caballero & Ramos-Portilla (2018).

1. Circulus present; antenna 5 segmented.................................................................... 2

- Circulus absent; antenna 6 segmented..................................................................... 3

2. Body setae clavate; anal ring setae flagellate; with 2 circuli................................................ baskyi

- Body setae flagellate; anal ring setae clavate; with 1 circulus............................................. epicopus

3. Multilocular disc pores present; body setae clavate, elongate, dilated only at tip; anal ring setae numbering 6–17..... coffeae

- Multilocular disc pores absent; body setae clavate to falcate, short, stout throughout length; anal ring setae numbering 18....................................................................................... udzungwensis sp. n.