Species key of Dirivultidae: <i>Aphotopontius</i>.

<p>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. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009801#pone-0009801-g001" target="_blank">Figure 1I</a> shows <i>A. acanthinus</i> 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 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0009801#pone-0009801-g001" target="_blank">Figure 1F</a>).