Medium-sized larvae, up to 8 mm long.
Antenna with 5 segments; segments 3 and 4 subequal in length and each longer than segment 5. Ring organ indistinct, on basal 1/4 of segment 1. Blade ending before apex of flagellum. Lauterborn organs indistinct or absent. Style longer than length of segment 3.
with SI bifid, remaining S setae simple. Labral lamellae absent. Chaetae serrate; spinulae simple. Pecten epipharyngis consisting of 3 scales. Chaetulae laterales simple; chaetulae basales with branched apices. Ungula V-shaped with oval basal sclerite. Premandible with 1-2 apical teeth; brush indistinct.
Apical tooth shorter than combined width of 3 inner teeth. Seta subdentalis simple, apically pointed or rounded. Seta interna with 6-7 simple to serrate branches. Outer margin smooth to weakly crenulate. Mola without spines.
Mentum with 1 median and 6 pairs of lateral teeth; convex with a rounded median tooth. Ventromental plate narrow; beard short, sparse and weak.
Maxilla palpiger with triangular chaetulae. Galea with simple to complex lamellae; pecten galearis absent. Seta maxillaris simple.
Body with anterior and posterior parapods separate, each with an apical group of simple claws. Procercus shorter to about as long as wide, bearing 5-6 anal setae; without spur. Anal tubules absent. Body setae simple.
Halocladius larvae develop in marine intertidal, brackish (dilute saline) or inland saline waters of the northern hemisphere. Densities can be high on marine algae in eastern Maritime Canada.