Small to medium-sized larvae, up to 6 mm long. Head yellow, body pale-green or yellowish; antennal segment 2 dark brown. Head capsule longish; cephalic index about 0.5. Dorsally DP absent, S7 ventral to S8 which is located dorsal to posterodorsal to S7; S5 posteriormost, but may be aligned obliquely to S7 and S8. Ventrally, SSm medial to closely-located S9, S10 and large, eye-shaped VP; S10 lateralmost, level or anterolateral to SSm. All setae (S5, S7, S8, S9, S10, SSm multibranched.
Distinctly longer than 1/2 length of head, 3.5x as long as mandible. Antennal ratio about 3.0. Basal segment about 9x as long as basal width, with ring organ at 0.6; segment 2 about 6x as long as wide, base almost 2x as wide as distal end; segment 3 2x as long as 4th. Style large, clubbed apically, extending to middle of segment 4. Peg sensilla as long as segment 3, seated opposite and fused with margin of 2nd segment to resemble shape of tuning fork. Blade and accessory blade of equal length, not extending beyond segment 3; basal ring 4x as high as wide.
Strongly curved, gradually narrowed towards apex. Apical tooth about 2.5x as long as maximum width, rather more than 1/3 length of mandible; inner margin of apical tooth with low lamella and large pointed inner tooth, both overlain by seta subdentalis; mola expanded to large tooth with apically-directed point. Ventrolateral setae aligned on outer margin of proximal 1/2 of mandible; seta 3 about midway between seta 2 and more proximal ring organ.
Basal segment of palp 3.5- 4x as long as wide, with ring organ at 0.5.
Without fringe of swim-setae. Anal tubules spindle-shaped, 3-4x as long as wide. Procercus brownish, 3x as long as wide with 7 apical setae. Claws of posterior parapod variable, often brownish or with 1 or more dark smaller claws. Larger claws with spinules on inner and /or outer margin; 1 or more smaller claws with smaller or larger tooth/teeth on inner margin.
Monopelopia belongs in the Pentaneurini, within a grouping of taxa with strong peg sensilla arising from antennal segment 2 like the ends of a tuning fork. As with Telmatopelopia and Xenopelopia, some posterior parapod claws have strong teeth on the inner margin. In contrast to the other genera, the granulose area at the base of the ligula is triangular rather than a transverse band, but ligula features do not distinguish all species of Monopelopia as suggested previously. The larva referred to as an “apparently undescribed, species of Monopelopia” in Epler and Janetzky (1999: 222) is the larva of Cantopelopia gesta. Epler (2001), in keying s.e. North American larvae, includes Cantopelopia gesta (Roback) on the basis that it is indistinguishable in larva or pupa from Monopelopia. Here we treat Cantopelopia, at most, as a subgenus of Monopelopia, distinguished from the nominate subgenus Monopelopia by all posterior parapod claws being pale, and with 3 smaller claws pectinate.
Larval Monopelopia of some Holarctic species live in small or very small pools of boggy acid water where according to Roback (1987) mosquito larvae, fungal spores and detritus form at least part of the diet. In Florida, Jamaica and the Neotropical region species live in the water of Bromeliaceae (bromeliad) plants.
In the Nearctic region 5 species are recorded: M. tillandsia, M. boliekae, M. tenuicalcar, M. gesta and M. caraguata. M. (Cantopelopia) gesta is distributed in eastern North America from Québec to Illinois and Florida: larvae have been collected from a creek in Georgia, from creeks and ponds in northern Florida and from sphagnum mats in an Ohio bog (Epler 2001). Monopelopia tenuicalcar is widespread in the western Palaearctic, and in the Nearctic from Canada (Newfoundland to British Columbia), California and Florida. In the Neotropical region M. boliekae is reported from Colombia (Spies and Reiss, 1996); an additional 4 taxa are recorded, M. mikeschwartzi from Jamaica (Epler and Janetzky, 1999), M. minuta (Serpa-Filho and Oliveira, 1997), M. caraguata (Mendes et al., 2003) and an undescribed species (Stur, 2000) from Brazil.
There are published records of the genus from the Oriental and Afrotropical regions. Undescribed species are known from sub-coastal pools in Thailand, billabongs in s.e. Australia, and tree-holes in New Zealand.