(Staeger, 1839)
Body
Medium sized larvae up to 9 mm long. Living larvae light-green or brownish. L4 setae are simpel. The anterior and posterior parapods are separate and bear rows of claws. The apical tooth of the small claws is shorter than the inner teeth Halocl variab claws. The procercus is present but the anal tubules are absent (Hirvenoja, 1973; Wiederholm, 1983; Moller Pillot, 1984b).
Head
Head slightly darkened (Hirvenoja, 1973).
Antenna
The antenna consists of five segments. The blade is shorter than the flagellum. Lauterborn organs are absent or not visible (Hirvenoja, 1973 ).
Mentum
The mentum has one median tooth and 6 pairs of lateral teeth. The median tooth is dome shaped. The second lateral is normal and not fused with the first lateral Halocl varians mentum. The ventromental plates are narrow. The beard is short and indistinct (Hirvenoja, 1973; Wiederholm, 1983; Moller Pillot, 1984b).
Labrum
The pecten epipharyngis consists of three scales, SI is plumose and the premandible has 1-2 apical teeth (Hirvenoja, 1973; Wiederholm, 1983; Moller Pillot, 1984b).
Mandible
The mandible has an apical tooth and 3 inner teeth. The seta interna has serrate branches (Wiederholm, 1983).
Differential characteristics
In brackish water the combination of missing anal tubules, a mentum with a normal 2nd lateral tooth and anteror parapods with small claws with an apical tooth shorter than the inner teeth Halocl variab claws is distinctive for Halocladius variabilis.