Antenna with 5 segments; segment 1 subequal to second; segment 4 longer than third. Blade slightly longer than flagellum. Lauterborn organs absent. Small style present.
Labrum with all S setae simple. Labral lamellae absent. Pecten epipharyngis consisting of 3 subequal spines. Chaetulae laterales consisting of 2 blunt spines and 1 complex spine. Premandible with 2 apical teeth and 2 inner teeth; single spine on inner margin; brush absent.
Apical tooth shorter than combined width of 3 inner teeth. Seta subdentalis and seta interna absent.
Mentum with 1 domed median tooth and 4 pairs of lateral teeth present; outermost tooth only a bulge on side of third lateral tooth. Ventromental plate small; beard absent.
Body with anterior parapods fused with few simple claws. Posterior parapods short but separate, bearing few simple claws. Procercus and anal setae absent.
Diagnosis based on Strenzke (1950d: 105) as 'Limnophyes' flexuella Edwards. No material examined.
Holarctic larval Mesosmittia probably are terrestrial, although a near certain identification has been made for larvae living on the wet surface of rainforest leaves in Australia and Brazil. The genus also is found in the Afrotropical region (Sæther 1996).