Ectoedemia similigena is very similar to E. turbidella and cannot be distinguished by external characters on the basis of the little material studied. The male genitalia have a distinctly longer valval tip than turbidella, and the gnathos is much narrower. The female genitalia have the posterior apophyses not reaching beyond the anterior ones and the signa are distinctly wider.
Male forewing length ca. 3.0 mm, antennal segments 55. Female forewing length 2.6 mm, antenna broken. Specimens too much worn or broken for detailed description, similar to E. turbidella, overall paler.
Male genitalia. Capsule length 325 μm. Tegumen produced into widely rounded pseuduncus. Gnathos with central element narrowly triangular, smooth. Valva length 215 μm, in ventral view with almost parallel sides, evenly curved towards demarcated, inwards curved tip, pointed and cut off at end. Aedeagus 365 μm long, very long (1.12 × capsule length) and stout, with two pairs of prominent carinae; ventral pair at extreme posterior tip, basally connected, pointed; dorsolateral pair more anteriorly placed, longer than ventral ones, strongly curved in lateral view, dorsally connected, slightly asymmetrical.
Female genitalia. T7 without row of setae, T8 relatively narrow, hardly tapering posteriorly, margins almost parallel, with two groups of ca 27 setae. Anal papillae narrow, with 14 setae in total. Anterior apophyses widened in middle. Posterior apophyses slightly widening anteriorly, not reaching beyond anterior ones. Vestibulum with vaginal sclerite, a dorsal spiculate pouch with many (ca 100) single, equally spaced, spines; and a patch of densely packed pectinations near entrance of ductus spermathecae. Corpus bursae small. ca 420 μm long, covered with small pectinations, except in anterior part; signa slightly dissimilar, 275 and 290 μm long, relatively wide (7–8 cells), ca 2.9 × as long as wide. Ductus spermathecae with 2.5 convolutions.
Hostplant unknown, a Populus is likely.
Ectoedemia similigena is only known from its type locality, Jalta botanical garden, on the Crimea (Ukraine). The species has not been found again, and we consider it possible that it is actually a species from somewhere in Central or Eastern Asia, introduced with plants.
Adults found in May.