Johannsen, 1905
Body
Medium sized larvae up to 10 mm long (Moller Pillot, 1984b). Living larvae are brownish. The L4 setae of the abdomen are short and simpel. The anterior and posterior parapods and procercus are present as are 4 anal tubules (Wiederholm, 1983).
Head
The head length is up to 0.9 mm (Moller Pillot, 1984b). The gula is yellow.
Antenna
The antenna consists of four segments. The second segment is divided in a short proximal part and a long distal part Bril antenna. The blade is subequal to the flagellum and the Lauterborn organs are distinct and situated on the apex of the second antennal segment.
Mentum
The mentum has two large median and 5 - 6 pairs of lateral teeth Between the median teeth usually a small toothlet is present Bril flavifrons mentum. The ventromental plates are weak and the beard is absent.
Labrum
The pecten epipharyngis consists of three scales, SI is plumose and labral lamellae consisting of 2 pectinate lobes. The premandible with two indistinct apical teeth (Wiederholm, 1983).
Mandible
The mandible with a distal tooth and 4 smaller teeth within. Seta interna with serrate to plumose branches (Wiederholm, 1983).
Differential characteristics
The divided second antennal segment Bril antenna separates Brillia from the other Orthocladiinae except from Heleniella. Brillia larvae are much larger and the antenna is 4 segmented (5 segments in Heleniella). B. flavifrons can easaly be separated from B. modesta by the yellow gula (B. modesta with a dark spot).