(Edwards, 1929)
Body
Medium sized to large larvae up to 8 mm long. The anterior and posterior parapods are separate. The parapods bear rows of claws. Procercus and two pairs of anal tubules present (Wiederholm, 1983; Moller Pillot, 1984b).
Head
The head length is 0.23 - 0.27 mm (Moller Pillot, 1984b).
Antenna
The antenna consists of five segments. The second segment is divided in a short proximal and a long distal part. The blade is twice as long the flagellum. Lauterborn organs are conspicuous Helen ornaticollis antenna.
Mentum
The mentum has two very large median teeth and 5 pairs of lateral teeth. The ventromental plates are small but well developed. The beard is absent Helen ornaticollais mentum.
Labrum
The pecten epipharyngis consists of three spines, SI is plumose with a central spinule longer than the others. The premandible has two apical teeth, one indistinct basal and an intermediate tooth (Wiederholm, 1983; Moller Pillot, 1984b).
Mandible
The mandible has an apical tooth and 3 inner teeth. The seta interna has branches (Wiederholm, 1983).
Differential characteristics
The antenna with a subdivided second segment Helen ornaticollis antenna is distinctive for Heleniella and Brillia only. The antenna of Heleniella consists of 5 segments where Brillia has only four.