Abstract
Epidermal glands are well-known in adult beetles, but their presence and function are less studied in larvae. This study reveals, for the first time for the family Leiodidae, the morphology and ultrastructure of epidermal, paired glands of abdominal segments present in larvae. They are documented in all larval stages of the scavenger beetle Sciodrepoides watsoni watsoni (using a multimodal microscopic approach: light and scanning electron, and transmission electron microscopy). Overview of these structures is also documented for other representatives of Leiodidae and Agyrtidae, basal lineages of the megadiverse Staphylinoidea. Structures differ in their position relative to a transverse cuticle fold, in the size and shape of the perforate cuticular area, and in the position and form of their openings. Their ultrastructure in Sciodrepoides watsoni watsoni strongly indicates a secretory function. All abdominal segmental glands are formed by a complex of (1) regular class 1 gland cells type 1, (2) modified class 1 cells type 2, with an apical reservoir-like invagination, and (3) class 3 gland units, consisting of one basal secretory cell plus a canal cell. All these glands have their own openings to the cuticle surface. Their secretions do not mix before their transport to the surface. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1038/s41598-026-41930-4.