Medium-sized larva, to 6.5 mm long. Frontoclypeal apotome anteriorly with undifferentiated sclerite.
Antenna 5-segmented, with 2-4 subequal and 5th shorter; A. R. 1.2-1.6; Ring organ close to base of segment 1; antennal blade double, longer branch not extending to antennal apex. Peg sensillum strong, inserted subapically, as long as Lauterborn organs, about 1/2 length of 3rd segment.
Labrum with SI palmate, perhaps fundamentally bifid, with each branch further divided into 2-4 lobes; SII-IV simple, SII fine, SIII long and blade-like. Chaetulae laterales all simple, basales apically branched. Pecten epipharyngis of 3 separate scales. Premandible with one broad apical tooth, without brush.
Mandible with outer and inner margins smooth, apical tooth subequal to slightly longer than combined width of 3 inner teeth. Seta subdentalis subovoid, hooked. Seta interna with 3 long simple branches and 3 shorter branches serrate.
Mentum distinct ventromentum comprising paired median teeth and somewhat appressed 1st laterals; dorsomentum with 5 pairs of lateral teeth on evenly-decreasing slope. Ventromental plate extending from mid first lateral teeth, narrow and not extending to outermost mental tooth; beard absent.
Maxilla with strong apodemes, palp small, squat; chaetulae of palpiger comprising numerous hyaline scales. Galea with numerous galear lamellae, predominantly simple scales, some pectinate; lacinial chaetae slightly serrate apically; antaxial setae long, fine; appendix distinct, broad, apically minutely trilobed.
Body with setation short and fine, excepting abdominal l4 seta, almost 200 microns long, plumose with 10-15 branches on III-V, unequally bifid on I, II, VII and VIII. Anterior parapods separate, with crown of elongate, simple longer spines and pectinate shorter claws. Posterior parapods separate, with apical group of simple claws. Procercus as wide as high, bicoloured, without spurs, bearing 2 moderate-lengthed median setae and 6-7 medium-length anal setae. Anal tubules short and globular or tapering to blunt point.
Parapsectrocladius appears at present to be exclusively Patagonian/S. Chilean in distribution, although sampling in the middle section of the Andes, where it might be expected at higher elevations, is less extensive than for the southern section. The limited sampling data suggests that at least one species is trans-Andean (P. longistilus), and given the high elevation of some sites, is likely for others.
Collection sites include both lotic (P. acuminatus) and lentic, ranging from relatively lowland volcanic lakes to high Andean glacial-fed pools, ponds and lakes. The study of Añón Suárez (1991) showed larvae of P. escondido (as Paratrissocladius nr acuminatus) to be one of the more abundant species in sediments in 1-3 metres depth in a small (8ha), relatively shallow (max. 7m), cool, dilute lake in the eastern slopes of the central Argentine Andes. Maximum densities of the species were found at 1.5m, where they approached 800 individuals per sq. metre.
Other species also appear to be lotic, including one taxon unidentified to species whose larvae were found in the marginal sediments of a glacial lake (Lago Frias, Argentina), and several species have been collected as adults during collections made at the margins of Chilean lakes at low elevation, the presumed habitat of the larvae.
The lotic habitat of immature specimens of P. acuminatus from Chiloe, s. Chile, is the only record from running water within the genus.