Large larvae, up to 11 mm long.
SIII arises from strong tubercle. Dorsal sclerites 1 and 2 distinct, anterior to interantennal sulcus
Antenna short, with 4 simple (non-annulate) segments; flagellum very short. Blade bifid, subequal to flagellum. Lauterborn organs small. Style weak.
All S setae simple and well developed. Labral lamellae absent but with anterior margin of labrum variably divided into 3 lobes. Chaetae in tuft of simple and/or serrate chaetae. Pecten epipharyngis consisting of 3 subequal scales, each with unequal teeth. Chaetulae laterales narrow, simple and serrate; chaetulae basales small or absent. Premandible broad, heavily sclerotized and with 3 apical teeth and well developed brush.
Single apical tooth scarcely longer than any of 4-6 inner teeth. Seta subdentalis long, extending nearly to apical tooth. Seta interna with 6 fine simple branches.
With single median tooth bearing median nipple; 4 to 6 pairs of lateral teeth, outermost often very small. Ventromental plate weak; beard absent.
Variable high numbers of tetrahedral lamellae, some simple, others apically serrate; present on outer margin of palpiger. Sensillae and setae of palp small and sited apically. Galea without lamellae or pecten galearis; sensillae and setae well developed.
Parapods well developed, each bearing crown of claws. Procercus absent, 2-3 anal setae absent. Body setae sometimes well developed, up to 1/2 segment length on thoracic segments.
As understood by the author, the genera Halirytus, Paraclunio and Psamathiomyia are synonyms of Telmatogeton.
Larvae of Telmatogeton can be found on most of the world's shores, where they make tubes within green algae such as Enteromorpha. They seem especially abundant in areas where there is some freshwater seepage, and/or where there is shelter from extreme wave exposure. Larvae are agonistic, defending their tubes against intruders, apparently seeking to optimise a pupation site.