Medium-sized to large, up to 12 mm long. Dark red to orange larvae.
Frontal apotome separated from clypeus of equally-width posteriorly, somewhat tapering anteriorly; labrum present, SIII complete, remaining labral area apparently fragmentary. Without frontal fenestra.
Antenna with 5 segments, diminishing in size distally, or 3rd and 4th subequal in length. Lauterborn organs about half length of segment 3, opposite on apex of 2nd segment, with style. Ring organ at basal 1/4 of segment 1, seta absent. Blade subequal to flagellum.
SI characteristic, slender, triangular in outline, plumose on inner side only (as Endochironomus); SII slender, feathered on both sides; SIII short, slender; SIV normally developed. Seta premandibularis branched. Labral lamellae normal. Pecten epipharyngis divided into 3 parts, each plate with several strong distal teeth and numerous further teeth on surface. Premandible with 2 apical and 1or indicated 2 inner teeth.
Mandible with obscure pale dorsal tooth; apical tooth slender, with 4 distinct inner teeth. Pecten mandibularis modestly developed, lamellae distally divided. Seta subdentalis inserted on ventral surface, simple, usually curved distally. Seta interna inserted on dorsal surface, plumose, multi-branched.
Mentum stated to have distinct dorsomentum of 4 protruding median teeth, with central 1-2 slightly lower than outer pair - however examination of reared S. luski shows the median area is not so delimited as stated; with 6 pairs of lateral teeth on each side, with 1st lower than 2nd and medians, then evenly decreasing in size laterally. Ventromental plates separated medially at least by width of median dorsomentum, relatively narrow and gently curved, with smooth anterior margin; striae continuous. Setae submenti simple.
Lateral and ventral tubules absent.
Synendotendipes was erected by Grodhaus (1987) for a Nearctic species luski Grodhaus that previously, on immature stages, would have been placed in Endochironomus (in the abranchius group). In reviewing the differences between his Synendotendipes and Endochironomus, Grodhaus cited the projecting median and first lateral teeth of the mentum, the four inner teeth of the mandible and the lack of tubercles on the anterior margin of the cardo.
Although Grodhaus did not examine the Palaearctic species placed previously on pupal characters in Endochironomus species group B, namely E. dispar Meigen, E. impar Walker, E. lepidus Meigen and E. abranchiatus Kieffer, he suggested they should be allocated to Synendotendipes. Examination of dispar and impar (concerning which there are some un resolved identificatory difficulties) indicates that these 2 species should be considered congeneric with S. luski, if generic status indeed is warranted.
The immature stages of Synendotendipes occur in standing and slowly flowing waters. S. luski was reared from larvae found in tangled littoral debris vegetation. S. lepidus may be an obligate leaf miner while S. dispar and perhaps also S. impar may be facultative leafminers. Moller-Pillot (1984) reviewed the ecology of the genus (as the E. dispar group). The genus is Holarctic, with 1 Nearctic species (S. luski) known from Manitoba to California and at least 3, perhaps 4, western Palaearctic species and 1 from Primorsky Krai, Russia.