Medium sized, 8+ mm long. Reddish-yellow larvae.
Frontoclypeal apotome without frontal fenestra, separated from labrum by convex anterior margin, remaining labral area fragmentary.
Antenna with 5 segments. Lauterborn organs opposite on apex of 2nd segment, with style. Ring organ in basal 1/4 of segment 1, seta absent. Blade as long as flagellum, accessory blade moderately long.
SI and SII plumose on both sides; SIII short, slender; SIV normally developed. Seta premandibularis simple. Labral lamellae normal. Pecten epipharyngis divided into 3 parts, each platelet distally serrate. Premandible with 3 teeth.
Mandible with all teeth black, Dorsal tooth relatively short, apical tooth and 3 inner teeth, mola proximal to basal inner tooth deeply notched. Pecten mandibularis modestly developed, lamellae distally divided. Seta subdentalis inserted on ventral surface, simple, long, slender. Seta interna inserted on dorsal surface, plumose, multi-branched.
Mentum glossy black, with distinct dorsomentum of 4 anteriorly-projecting median teeth, of which central 2 are lower than outer pair; 6 pairs of lateral teeth on each side, with 1st lower than 2nd, then decreasing in size laterally to small appressed pair of outermost teeth. Ventromental plates medially connected to median mentum, and thus separated medially by width of median section, broad and semi-lunar, with smooth anterior margin; striae continuous. Setae submenti simple.
Lateral and ventral tubules absent.
Phaenopsectra larvae may be readily separated from the similar larvae of Tribelos by the absence of labral sclerite 1 and the 3 plates of the pecten epipharyngis, which are serrated only distally. The most closely related genus, Sergentia, invariably has 4 rather than 3 inner mandibular teeth.
Larvae of Phaenopsectra occur in sandy and muddy sediments of small standing waters and flowing waters. They also occur in "Aufwuchs" of submerged water plants and hard substrata.
The genus has a Holarctic distribution. In the Palaearctic there are at least three species, in the Nearctic there are nine, with some species in common. Whether all Nearctic species belong to Phaenopsectra is questionable.