Small to large-sized larvae, to 9 mm long.
SI condition undescribed.
Antenna with 5 segments on a tall pedestal with (usually) or without basal tooth or spur of between 10 and 40 microns in length. Antennal ratio much greater than 1. Ring organ basal on 1st antennal segment, which is often curved. Seta short. Lauterborn organs small on long stems inserted opposite on apex of elongate cylindrical 2nd segment. Subsequent segments shorter than 2nd. Antennal blade usually no longer than 2nd segment, accessory blade short. Style on apex of 2nd segment, shorter than segment 3.
SI seta comb-like, fused at bases, SII on large pedestal, weakly plumose, perhaps sometimes simple, SIII short, simple, SIV present. Labral lamellae well developed. Pecten epipharyngis comprising 3 distally serrate scales. Premandible bifid, brush strong.
Mandible with dorsal tooth apical tooth and 3 pointed inner teeth, all dark. Seta subdentalis long, sinuous, reaching tip of apical tooth. Seta interna of 4 plumose branches. Pecten mandibularis well developed with many branched lamellae.
Mentum with laterally notched to almost trifid median tooth somewhat paler than 5 pair of laterals, which regularly decrease in size laterad. Ventromental plates close together medially, slightly wider than mentum, with fine striae.
Without tubules. Claws of posterior parapod simple, dense, arranged in single to multiple rows in horse-shoe shape.
As phylogenetic analyses using mitochondrial and nuclear DNA sequences have become available, definition and boundaries between Micropsectra, Krenopsectra and Parapsectra have disappeared, leaving Micropsectra paraphyletic with respect to the other two genera (Ekrem et al. 2010). The synonymy of these taxa is accepted here.
Considerable difficulty has previously been encountered in separating Micropsectra larvae from those of Tanytarsus. Generally the presence of a projection on the antennal pedestal has been used to characterize the genus Micropsectra. However, such a projection also occurs in some Tanytarsus species and is not always present in Micropsectra. The best character for separating these genera is the form of the premandible (bifid in the broadest defined Micropsectra, trifid in Tanytarsus). If the premandible cannot be viewed adequately, the dense ‘horseshoe’ of a hundred or so claws on the posterior parapods, all simple in multiple rows, is a useful indication for Micropsectra (versus Tanytarsus with fewer (up to 30) in a simple ‘horse-shoe’).
The genus has been divided into several species groups on the basis of adult and pupal morphology (Reiss 1969c, Sawedal 1976a). However too few larvae have been reared to understand the validity (or not) of these groups.
Micropsectra spp. have been recorded from a wide range of habitats, including hygropetric situations, thermal springs and temporary pools. They are particularly characteristic of muddy deposits in slack regions of streams and small rivers (rhithron) and of mesotrophic-oligotrophic lakes, including the profundal zone.
Many species are cold stenothermic and are recorded in or near coldwater springs. Species previously allocated to Krenopsectra and Parapsectra are found in springs, brooks and small streams, Parapsectra also in moorland pools. The three genera combined have a Holarctic distribution and about 100 valid species have been described. Comparably few of these are described as larvae.