The structure of a gilled stonefly larva from the mid-Cretaceous Kachin amber.

Perlidae stands as the most diverse family within Plecoptera, with evidence suggesting possible adaptation to warmer aquatic environments. Tracheal gills are hypothesized to have played a pivotal role in this radiation process. This study presents the description of a fossilized stonefly larva with gills, preserved as a fresh exuvia in mid-Cretaceous Kachin amber from northern Myanmar. The larva was classified within the family Perlidae based on distinctive morphological traits, including toothed lacinia and sharp-cusped mandibles, slender palps, glossae shorter than rounded paraglossae, and highly branched gills on the sides and ventral surface of thoracic segments. Additionally, the presence of a transverse, sparse, and irregular setal row on the occiput further indicates classification within the subfamily Acroneuriinae. Notably, the fossilized larva displays striking similarities in gill morphology and distribution to certain extant members within Perlidae, suggesting that these gill structures have an advantage in various aquatic habitats.