Megacentron possible Freeman

Description

Introduction

Large sized, up to 10 mm long, red. Head capsule golden to brown; mentum and mandibular teeth darker. Labral margin, premandible and some dorsal sclerites darkened.

Dorsal Head

S3 seta on fragmented clypeus separate from frontal apotome; labral sclerites distinct.

Antenna

Antenna with 5 segments, segment 2 shorter than 3rd, 4th subequal to 2nd, 5th small. AR c. 1. Ring organ in basal 1/4 - 1/3 of segment 1, seta absent. Blade apparently always distorted, perhaps extending to sub apex of antenna, accessory blade unobserved. Lauterborn organs short, opposite on apex of 2nd segment. Style unobserved.

Labrum

SI broadly plumose, with common base; SII longer, narrowly plumose; SIII plumose; SIVa and b well developed. Seta premandibularis stout, simple. Labral lamellae broad, without indication of median division, with c 30 teeth. Pecten epipharyngis of three digitiform scales (perhaps basally with indication of microteeth). Chaetulae laterales short, simple, few; 2 apically branched chaetulae basales. Premandible with 2 teeth and strong brush.

Mandible

Dorsal tooth absent, with short apical tooth and 4 similarly dark, rounded inner teeth. Pecten mandibularis very weak. Seta subdentalis inserted on dorsal surface, long, curved extending to base of apical mandibular tooth. Outer margin, mola and inner margin smooth. Seta interna strongly plumose, inserted as usual on dorsal surface.

Mentum

Mentum with rounded recessed median tooth, protruding larger rounded 1st laterals, laterals evenly sloping from 1st to outermost (5th). Ventromental plates quite broad, shorter than mentum width, separated medially by 5 median mental teeth, evenly striate with dense, more or less parallel striae. Setae submenti simple.

Body

Abdomen without prominent body setae; anterior parapods short, separate with dense simple hair-like claws; posterior parapods separate with crown of sparse curved simple claws. Procerci squat, as high as wide, bearing 2 lateral setae and 7 apical setae, no longer than 2x segment bearing procercus.

Notes

Taxonomic Notes

The larvae putatively identified as belonging to Megacentron have the gestalt of Pseudochironomini, including showing the seta interna inserted on the inner (dorsal) side of the mandible. The larvae differ from Riethia, and thus could belong to the only other Australian genus potentially allocated to Pseudochironomini, namely Megacentron Freeman.

Ecological Notes

Larvae come from a single site in New South Wales, Australia - Chandler's Creek, from a 'log wash' sample - but the gut contents is not wood fibre.

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