Through an analysis of the primary setae and pores of first-instar larvae of 31 genera of Hydroporinae, and 22 genera belonging to other dytiscid subfamilies, the ancestral system of primary setae and pores of the maxilla of the Hydroporinae is reconsidered. Fourteen setae and seven pores have been assigned to the ground plan pattern of the hydroporine maxilla. Larvae of Hydroporinae differ from those of other Dytiscidae in the absence of the primary pores MXa, MXb, MXc and MXd, and in the presence of the primary pore MXk.