Potthastia gaedii type group Meigen

Description

Introduction

Medium sized to large larvae, up to 10 mm long.

Antenna

With 5 segments; segment 5 longer than segment 4; division between segments 2 and 3 indistinct with annulations continuing onto segment 2. Lauterborn organs small. Style about as long as segment 3.

Labrum

With SI lamelliform; SIII simple. Bisensillae posterodorsal to SIV absent. Labral lamellae consisting of 1 pair of broad, subtriangular and transparent lobes. Chaetae deeply divided, some branches very long; chaeta media not distinctive; four pairs of short, simple spinulae present. Pecten epipharyngis consisting of 3 long, pointed scales, lateral pair partly overlapping median scale. Chaetulae laterales forming arched group on either side of pecten epipharyngis. Ungula semicircular; basal sclerite vestigial or absent. Premandible narrow, simple, with dark apical half; lateral spine present.

Mandible

Apical tooth shorter than combined width of 4 inner teeth. Seta interna with 16-21 serrate branches.

Mentum

With very broad, dome-shaped median tooth and 8 pairs of lateral teeth; median tooth and first lateral tooth pale, remaining lateral teeth blackish; median tooth 5-6x as wide as first lateral tooth. Ventromental plate extending laterally to mental teeth; anteromedial apex extending about level of first lateral tooth, often appearing to be continuous with first lateral and median teeth. Setae submenti arising closer to mentum than to postoccipital margin.

Maxilla

With palp about as long as wide with rounded sides. Chaetulae of palpiger consisting of flat scales. Galea with row of peg-like lamellae on anterior margin and a tuft of setose chaetulae on dorsal surface. Setae maxillaris simple.

Body

With anterior and posterior parapods separate, each bearing an apical crown of claws. Procercus small, about as long as wide, with strongly sclerotized posterior margin and 6-7 anal setae and 2 subapical setae; anal setae at most as long as preanal segment. Supraanal setae strong. Body setae pale and indistinct.

Notes

Taxonomic Notes

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.

Ecological Notes

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.

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