Medium-sized larvae, up to 9 mm long. Head yellowish-brown, in some species partially dark brown in proximal 1/3; body yellowish-brown with darker spots. Head capsule slender; cephalic index 0.5. Dorsally DP absent; S5 nearly directly mesial to S8 and both posteromesial to S7. Ventrally S9-S10-SSm tending to form curved line, with large, eye-shaped VP posterior or posterolateral to alignment. All setae simple.
Half as long as head, 3.5x as long as mandible. Antennal ratio 2.6-3.4. Basal segment about 11x as long as wide, with ring organ at 0.5; segment 2 about 14x as long as wide; segment 3 4x as long as wide, scarcely longer than last segment. Style almost as long as segments 3 and 4 combined. Peg sensilla large, blunt apically, about 2/3 length of segment 3. Blade and accessory blade as long as flagellum; basal ring about 3x as long as wide.
Moderately curved, gradually narrowed towards apex. Apical tooth about 3x as long as basal width, 1/3 length of mandible. Inner tooth large, conical, extending over long seta subdentalis; mola strongly expanded into large, blunt, tooth; accessory tooth at base of mola. Ventrolateral setae closely aligned on proximal 1/3 of mandible; seta 1 with very small pit, 2 and 3 simple; seta 3 situated halfway between seta 1 and ring organ.
Basal segment of palp 4x as long as wide; ring organ at 0.6.
Without fringe of swim-setae. Anal tubules spindle-shaped. Procercus dark brown, at least posteriorly, with 7 dark apical setae. Claws of posterior parapod all pale, larger claws with small spinules on inner and/or outer margin; often with 1 smaller claw bifid, ventral spine always smaller and weaker than dorsal tooth (some eastern North American and extralimital species may have only simple claws); basal section of some claws with outer and, sometimes, inner margins, lamellate.
Zavrelimyia belongs to the Pentaneurini. The rather similar Paramerina shares many features including the arrangement of cephalic setation and pits, and the very broad pseudoradula. Larval Paramerina differ mainly in the maxillary palp being subdivided into 2 sclerotised segments. Zavrelimyia often may be separated by the posterior parapod claws being pale, with at least one claw clearly bifid with shorter inner tooth, but the structure in some species of Paramerina, may be similar. Furthermore, such a claw is absent in Z. bifasciata (Coquillett) and some Z. thryptica complex larvae, present or absent in Reomyia (see below) and present in one undoubted larval Paramerina (q.v.). Unassociated Paramerina-like larvae from Thailand with an undivided palp may further complicate distinction between larval Paramerina and Zavrelimyia.
Reomyia was described by Roback (1986c) for western North American Z. wartinbei Roback: the pupa was included in Fittkau and Murray (1986) as Tanypodinae genus III. Although the larva is undescribed formally, Epler (2001) illustrates and discusses the morphology, arguing that reared specimens from North Carolina blur generic distinction from Zavrelimyia. Apparently intra-specific variation in presence of a bifid claw adds further to the difficulty in diagnosis. Epler (2001) suggests treating Reomyia as, at most, a subgenus of Zavrelimyia and here this revised status is adopted. As a larva, Z. (Reomyia) may be distinguishable by the maxillary palp, in which the ring organ is closer to the base (0.3-0.4) in a more elongate (c 6x as long as wide) palp compared to Z. (Z. s. str.) (0.5-0.7 in palp 4x as long as wide) (Epler 2001).
Larvae of Zavrelimyia are, with few exceptions (nubila group of Fittkau 1962), more or less cold stenothermic and in temperate regions of the Holarctic primarily inhabitants of sandy or detritus rich sediments of springs and of lentic habitats of stream sections close to springs. In cooler regions they also inhabit lower reaches of streams and the littoral of lakes. Zavrelimyia may be one of the most abundant genera of Tanypodinae in suitable habitats.
Zavrelimyia is represented by 11 species in the Palaearctic, several, e.g. Z. barbatipes, Z. hirtimana and Z. nubila, are widespread in the western Palaearctic, others are more restricted, for example, to Japan. Three species are known from North America, but Z. thryptica and Z. sinuousa may comprise complexes, and a s.e. larva ('sp. A') constitutes another unreared species (Epler, 2001). Unnamed species are reported with varying confidence from Brazil, Colombia, Costa Rica and Ecuador. Two species, Z. facilis and Z. alterna, are described from springs in Indonesia and an unequivocal larval/pupal association indicates the genus is present in Thailand.
Pupae of Z. (Reomyia) were obtained from a small stream on Kodiak Island, Alaska, and there is an additional record from the Alaskan mainland. However more recent sites for the larva in North and South Carolina (Epler 2001), Oregon and California suggest these are not as cold stenothermic as once believed.