Key to the species of Apoprionospio

1. Dorsal crest on chaetiger 7 present........................................................................ 2

- Dorsal crest on chaetiger 7 absent................................................ A. pygmaea (Hartman, 1961)

2. Prostomium triangular, broadly flared; secondary hoods of hooded hooks absent............... A. sanguarensis sp. nov.

- Prostomium subtriangular, widest anteriorly; secondary hoods of hooded hooks present............................. 3

3. Peristomium separated of chaetiger 1; neuropodial lamellae on chaetiger 2 rounded........... A. japonica Imajima, 1989

- Peristomium fused of chaetiger 1; neuropodial lamellae on chaetiger 2 triangular................... A. dayi Foster, 1969