(Kieffer, 1925)
Body
Medium sized larvae with a length up to 8 mm. Slender larvae 12x as long as wide. Procercus is exceptionally long and about 10x as long as the basal width, with a blackish posterior part Lasiodiamesa procercus. The anal setae are shorter than the procercus. On the 11 segment 2 small spiracular rings (Wiederholm, 1983).
Head
Antenna
The antenna consists of 5 segments with the basal segment 5 x as long as the basal width. Segment 2 and 3 subequal. Segment 3 almost entirely annulated and segment 4 indistinctly separated and probably very small. Fifth segment normal Lasiodiamesa antenna (Wiederholm, 1983).
Mentum
Mentum with a prominent medial tooth and 15 pairs of lateral teeth. The 3 outer pairs extremely small Lasiodiamesa mentum (Wiederholm, 1983).
Labrum
SI is a simpel stout tubercle and pecten epipharyngis with 5 long and slender spines (Wiederholm, 1983).
Mandible
The mandible with a dorsal tooth, an apical tooth and 9 inner teeth. Seta interna with 17-30 branches (Wiederholm, 1983).
Maxilla
The maxilla is very long with the basal segment of the maxilla is subdivided in 2 - 6 segments (Wiederholm, 1983).
Anal tubules
4 anal tubules which are longer than wide (Wiederholm, 1983).
Posterior parapods
Some claws on posterior parapods may be brown. No teeth on the inner margin (Wiederholm, 1983).
Differential characteristics
Lasiodiamesa is easy to identify by the long procercus and the mentum with 15 pairs of lateral teeth.