Medium-sized larva, up to 7 mm long, body red in life. Head pale brown. Head capsule longish; cephalic index 0.5. Dorsal setae undescribed; Ventrally SSm, S9 and S10 near aligned diagonally, VP posterior to S10, lateral or slightly postero-lateral to SSm.
Not quite 1/2 as long as head, slightly more than 3.5x as long as mandible. Antennal ratio 2.7-2.9. Basal segment length v basal width ratio undescribed, with ring organ at 0.6; segment 2 about 12x as long as wide, broader at base; segment 3 2.5x as long as wide, about as long as last segment. Style extends to middle of last segment. Peg sensilla large, situated opposite each other, as long as segment 3, tightly fused to margin of segment 2, with shape similar to tuning fork. Blade and accessory blade subequal, extending near to antennal apex; basal ring of blade 3x as high as wide.
Moderately curved, narrowed towards apex. Apical tooth 2.75x as long as basal width, 0.3x length of mandible, with smooth lamella on ventral base extending to well-developed inner tooth; mola produced strongly to bluntly-rounded apex; seta subdentalis strong. Ventrolateral setae aligned on outer margin, in distal 1/3 of basal 1/2 of mandible; seta 1 simple peg, close to simple seta 2; Ring organ situated proximal to simple seta 3, and as distant from seta 3 as the latter is from seta 2.
Basal segment of palp 4.5-5x as long as wide, with ring organ at 0.6-0.7.
Without fringe of swim-setae. Anal tubules greater than 4x as long as wide, slightly shorter than width of posterior parapod. Procercus about 4-5x as long as wide, with 7 apical setae. Claws of posterior parapod all pale-brown; 2 shortest claws with several strong inner teeth and some spinules on outer margin; 3 slightly larger claws with 1 internal spine, largest narrow, finely pectinate.
Larvae of Denopelopia are pentaneurine tanypods, distinguished by the large peg sensilla “fused” to the apex of antennal segment 2, giving a tuning fork-like appearance. Within this group, the larva is distinguished by the trifid paraligula and all posterior parapod claws being pale with 2 small claws bearing a large inner tooth. Roback and Rutter (1988) tabulate some characters potentially differentiating from similar taxa.
The genus, including Yaequintus Sasa & Suzuki (Kobayashi and Endo, 2008), occurs in the Americas and the eastern Palaearctic and part of the oriental region. The type locality of the type species Denopelopia atria in Punta Gorda, Florida is a shallow drainage ditch with imperceptible flow amongst Typha with low DO and high iron levels.
In North America, the most northerly specimens are from the Orlando, Florida area (Epler, 2001). Denopelopia atria has been reared from a vegetation-choked pond in a cattle pasture in southwestern Costa Rica (Epler 2001), and unreared larvae of the genus are reported from Panama and southern Brazilian wetlands. In Asia, Denopelopia is represented by 3 species known only from adult males, one of which, Yaequintus irioquereus from southernmost Japan, is synonymous with a Chinese species described by Cheng and Wang (2005) (Kobayashi and Endo, 2008).