Potthastia longimanus type group
Medium sized to large larvae, up to 10 mm long.
With 5 segments; segment 2 longer than segment 1; segment 5 longer than or subequal in length to segment 4; segment 3 annulated. Lauterborn organs small. Style as long as combined lengths of segments 3 and 4.
With SI long and narrow; SIII simple. Two pairs of bisensillae present dorsolateral to SIV. One pair of bifid to trifid labral lamellae present. Chaetae absent; about 6 pairs of pointed spinulae present. Pecten epipharyngis consisting of 3 long, narrow, and pointed scales. Chaetulae laterales narrow and pointed. Ungula narrow, elongate; basal sclerite vestigial or absent. Premandible apically broad with about 15 fine, pointed teeth; lateral spine present.
Attenuated apically with hooked apical tooth much longer than combined width of inner teeth; 3 short pointed inner teeth immediately distal to base of long, narrow seta subdentalis. Hook-shaped process arising dorsal to distal inner tooth. Seta interna absent.
With anteroventral margin of head capsule without teeth. No ventromental plate apparent, although anterior margin of mentum may be fused ventromental plates. Setae submenti arising closer to mentum than to postoccipital margin.
With chaetulae of palpiger apically pectinate. Galea apparently without lamellae. Setae maxillaris simple.
With anterior and posterior parapods separate, each bearing an apical crown of claws. Procercus shorter than wide, strongly sclerotized and bearing 5-7 anal setae and 2 subapical setae; anal setae short, about as long as preanal segment. Supraanal setae strong. Body setae pale and indistinct.
Larvae of the two groups of Potthastia (gaedii and longimanus) are distinctive and suggest the taxonomy of Potthastia needs to be revisited. Larvae of the P. longimanus group are unique amongst the Diamesini in having a toothless mentum, apically attenuated mandible, long 2nd antennal segment and bifid to trifid labral lamellae. Larvae of the P. gaedii group are more typical diamesines and resemble those of Sympotthastia (q.v.). They may be distinguished by the broad dome-shaped median tooth of the mentum and the presence pf peg-like lamellae on the galea. The median tooth and first lateral tooth are light coloured, contrasting sharply with the dark lateral teeth.
Larvae of all Potthastia inhabit flowing waters of all sizes. Those of the P.longimanus group also inhabit lakes. At least 5 species occur, all in the Holarctic.