The interactions between mites and fungi encompass a wide range of ecological dynamics, from mere transport to more complex mutualistic associations. Key evidence of such coevolution is the presence of specialized structures for carrying spores, known as sporothecae - baggy, membranous, and eversible spore sacks - first described by Suski in the genus Siteroptes. These structures have subsequently been identified in several mite groups, including Heterostigmatina (Trombidiformes), varying in shape and placement. However, despite known interactions between Eriophyoidea mites and fungi, no specialized transport structures have been observed. This study reports for the first time the presence of sporothecae in a new Phytoptidae mite of the genus Trisetacus, associated with an endemic Juniperus species in the Azores archipelago. During a survey of the acarofauna associated with invasive and endemic plants in the Azores, a new species of Trisetacus (Eriophyoidea) were found associated with the endemic Azorean juniper Juniperus brevifolia (Seub.) Antoine in four islands - Flores, Graciosa, Faial and São Miguel - during spring and summer 2024–2025. Berlese- modified mounted specimens were examined examined under a Leica DMLB phase-contrast and DIC microscope. Among the 25 mounted specimens examined (24 females and 1 male), fungal spores within paired invaginations posterior to coxae II were observed in 11 females. In some specimens, the invaginations were partially open, revealing sac-like cavities that consistently contained fungal spores (one to six per cavity). The fungal spores observed within Trisetacus sporothecae appear to be morphologically uniform, although their identity remains undetermined. The wide phylogenetic divergence between Phytoptidae and other mite lineages, such as Heterostigmatina, suggests an independent evolutionary origin of sporothecae. Molecular identification of the fungal spores stored within the Trisetacus sporothecae will provide further insights into this ecological interaction. Considering the high host specificity of eriophyoid mites and that they do not feed directly on fungi — unlike other mite groups — we hypothesize that this interaction could represent a potential indirect mutualistic association between mites, fungi, and host plants, although its functional significance remains unknown.