Lepidoptera (moths and butterflies) are among the top three most species-rich orders of insects with 173689 species at the latest count (Lees and Zilli 2025, see also van Nieukerken et al. 2011). Together with its sister order Trichoptera (caddisflies) and the recently described fossil order Tarachoptera, Lepidoptera are grouped as Amphiesmenoptera (Hennig 1969; Mey et al. 2017), which group is subtended by the proposed, although weakly supported stem lineage Protomeroptera (Engel 2022; Wang et al. 2022). For a long time, non-glossatan, mandibulate moths have been recognized as the primitive state, and glossatan Lepidoptera as the derived ones. Other primitive characters are homoneurous venation and jugate wing coupling. Extant non-glossatan families are Micropterigidae, Agathiphagidae, and Heterobathmiidae, each also given suborder status (Kristensen et al. 2007; van Nieukerken et al. 2011). Molecular genetic studies support the early diverging status of these families (Regier et al. 2013; Wahlberg et al. 2013; Mitter et al. 2017; Kawahara et al. 2019, 2022).

The lepidopteran fossil record essentially comes from four sources. Fine-laminated sediments allow the preservation of larger external structures, mostly important for systematics their wing venation. Much better in preservation are most findings of Lepidoptera from ambers, often with optimal preservation of all external structures. Another line of evidence is from larval leaf mines in fossil leaves, again mainly from fine-laminated sediments. However, this kind of evidence is often unreliable since also other orders like Diptera, Hymenoptera and Coleoptera produce such leaf mines (Hering 1951; Knecht et al. 2023). Scales isolated from sediments have provided other insights on early lepidopteran evolution, and that of other orders with scales (van Eldijk et al. 2018).

All records of fossil Lepidoptera were last reviewed by Sohn et al. (2012) and Sohn and Lamas (2013); all taxa described from Cretaceous Burmese amber have more recently been summarized by Ross (2023, 2025).

The amber with the imago described here is kept in a sealed plastic bag inside a metal box, excluding access of air and light, currently being kept in the collection of the author TF, to be transferred to the Bavarian State Collection of Natural History upon publication under # SNSB-BSPG 2026 I 9.

The inclusion was photographed by Aleksej Damzen with a Canon 90D camera with Canon lens MP-E-65 and Helicon Focus software used. For the line drawing, a print-out was used to faciliate hand-drawing of the wing venation.

Authenticity of the specimen was ensured by obtaining it from a trusted amber dealer known to TCF from a long-term relationship. Furthermore, the amber contains Quercus-type trichomes typical for Baltic amber.

Compared to other Lepidoptera from Baltic amber, this is an extremely rare finding, being one specimen among some 2000 Lepidoptera recovered from succinites (Baltic, Rovno and Bitterfeld) and one among 30 Micropterigidae from Baltic amber in the collection of author TCF.

Glaesopterix has also been compared with other lineages of Amphiesmenoptera, including Tarachoptera, Trichoptera and basal Lepidoptera (data not shown). Its assignment to Micropterigidae is, however, beyond any doubt.

Most puzzling about this finding is its unique combination of characters which are found in various lineages of Micropterigidae (Table 1).

Micropterigidae are assumed to be the most basal extant family of Lepidoptera. They possess, however, a number of autapomorphies (Kristensen and Skalski 1999; Hashimoto 2006). Some of them are recognizable also in fossils and allow therefore their assignment to the family. In Glaesopterix, the following of these characters have been found:

(1) Swollen pedicel; (2) labial palpi reduced; (3) spur formula 0-0-4; (4) crossvein M-Cu lost in hindwing. A very characteristic apomorphy of the family, the ascoid sensillae on the antennomeres, however, could not be identified. They could also not be found in other fossil genera of Micropterigidae.

Gibbs et al. (2004) have recognized five different lineages within Micropterigidae, based on the investigation of the 16S rRNA. Up to date, no comprehensive study has been performed, however, to recognize external characters as autapomorphies of each these lineages, except for the morphometric analysis performed by Han et al. (2024). It has been attempted here to identify simple external apomorphies and to correlate them with characters found in Glaesopterix (Table 1), including Agathiphagidae and the two genera recently transferred to Heterobathmiidae, i.e. Palaeosabatinca and Parasabatinca, according to Han et al. 2025).

Supposed apomorphies of the five linages of Micropterigidae (+: found in Glaesopterix, -: not found in Glaesopterix):

Australian lineage: (1) apical crossvein Sc-R absent in forewing (+); (2) humeral vein absent (-); (3) Sc-R fused in hindwing (-).

Southern sabatincoid lineage: (1) labial palpi < 3-segmented (+); (2) Sc-R fused in hindwing (-).

Sabatinca s.str.: (1) scapus with median indentation (-), (2) Sc-R fused in hindwing (-), (3) cell open in hindwing (+), (4) male abdominal V 8 absent (+).

Northern hemisphere genera: (1) labial palpi < 3-segmented (+); (2) R unforked in forewing (-); (3) cell open in forewing (partim, -), (4) crossvein R-M very short in forewing (partim, +); (5) Sc-R fused in hindwing (-); (6) male abdominal V VIII absent (+); (9) epiphysis lost (partim, -), (10) flagellomeres modified (-).

Micropterix-lineage: (1) labial palpi < 3-segmented (+); (2) R unforked in forewing (-); (3) Rs4 preapical in forewing (-); (4) crossvein R-M very short (partim, +); (5) basal crossvein M-CuP absent (-); (6) Rs4 preapical in hindwing (partim, -), (7) abdominal S 5 gland absent (+); (8) valvae elongated (-).

The above analysis does not allow a definite assignment of Glaesopterix to any of the five lineages of Micropterigidae, although the relations to the three southern hemisphere lineages seem to be weak. The northern hemisphere genera and the Micropterix-lineage, however, seem to have more correlations to the new genus, which has a somewhat intermediate and therefore maybe basal state between these two lineages. For more data and discussion of Micropterix consider Kurz and Fischer (2026). Glaesopterix itself, furthermore, does not show any autapomorphies of its own, because all its apomorphic characters are shared with at least one of the other lineages (see also diagnosis).

The new genus Glaesopterix, based on a well-preserved single male imago from Eocene Baltic amber, exhibits a previously unknown character combination in the family, but is not a member of one of the five currently recognized lineages of Micropterigidae. Rather, it represents a separate lineage closer to the Northern and the Micropterix lineages, than to the Southern ones.