Small larvae, up to 5 mm long. Head with or without brown or black markings; body pale; procercus partly darkened; anal setae and setae of posterior parapod brownish black; claws yellow. Head capsule slender, almost rectangular; cephalic index 0.40-0.44; surface smooth or granulose: proximal to middle of head, more-or-less flattened hump on either side, with or without small, anteriorly-directed spinules. Dorsally DP absent, S7, S8 and S5 near aligned. SSm forming almost straight line with S10 and S9, VP variably posterior to S9. All setae simple and short.
Relatively long, 3/5 length of head, 3.5x as long as mandible. Antennal ratio 2.0-2.5. Basal segment about 12x as long as basal width, with ring organ at 0.8; segment 2 about 10.5x as long as wide; segment 3 3x as long as wide, about 1/3 longer than apical segment. Style cylindrical in basal 1/2, apical part somewhat swollen. Peg sensilla 1/2 as long as segment 3. Blade somewhat longer than segment 2, over-reached by accessory blade; basal ring 2.5x as high as wide.
Strongly curved, strongly narrowed in apical 1/2. Apical tooth almost 3x as long as basal width; inner margin with low lamella. Inner tooth very large, apically directed; small accessory tooth associated with median sub-apex of mola; mola developed as large, protruding, blunt-ended tooth; seta subdentalis recurved. Ventrolateral setae and ring organ aligned, roughly equidistant to one another, in proximal 1/2 of mandible.
Basal segment of palp 2-4x as long as wide, ring organ at about 0.85-0.9.
Without fringe of swim-setae. Anal tubules almost as long as posterior parapods. Preanal setae as long as posterior parapods. Seta of posterior parapod about 1/2 length of parapod, at base with or without smaller or larger, long spinules. Procercus 3.5-6x as long as wide, with 7 dark apical setae. Claws of posterior parapod yellow; larger claws with fine spines on inner and/or outer margin, one with slender, drawn-out apex; one small claws bifid, dorsal tooth shorter and weaker than ventral tooth.
Labrundinia belongs to the Pentaneurini, and resembles Nilotanypus in the shape of ligula (with middle tooth longer than short inner teeth) and the large inner and molar mandibular teeth: both have very long, slender anal tubules. The flat spinose hump laterally on the head, and the single, bifid claw with longer inner tooth on the posterior parapod diagnose Labrundinia. Many Zavrelimyia and some Paramerina have similar claws, but in these, the ventral not dorsal tooth is smaller. The proportions of the ligula, palp and procercus are exceptionally variable within the genus.
Epler (2001) keys 12 named and unnamed larval types and provides ecological notes on much of this undescribed diversity in the s.e. USA.
Larvae of Labrundinia live in small, standing water bodies as well as in streams and rivers. The only European species (L. longipalipis), has a preference for bogs. The genus is especially abundant in the New World sub-tropics and tropics. Labrundinia larvae are abundant associates with macrophytes in standing waters in southern USA and ox-bow lakes in Brazil. Although 6 species are named from the Nearctic, Epler (2001) reports 12 distinct, identifiable larval types from the s.e. USA. Named species based on adults (Roback, 1987) and many undescribed larvae are known from Central (Watson and Heyn, 1993) and South America. Although Labrundinia separata from Argentina is the only named species from South America, Brazil especially has undescribed high diversity. One larva has been described from Sumatra, Indonesia.