Species key of Dirivultidae: Aphotopontius.

First, species of this genus can be distinguished by the ratio of length to width of the caudal ramus (caudal ramus l∶w). Second, species can be discriminated by the presence or absence of spiniform processes (S) on the genital somite of female (f) and male (m) (e.g. Figure 1I shows A. acanthinus with a caudal ramus ratio of length∶width with 2∶1; the female genital double somite has spiniform processes). Other species characters include the shape of various parts of the body (i.e. the maxilliped (mxp), see Figure 1F).