Hosted at the University of the Azores, the "Dalberto Teixeira Pombo" Collection (DTP) is an invaluable repository showcasing the diversity of arthropods from the Azores Archipelago, Portugal. This collection not only preserves a vital record of the region's arthropological heritage but also underpins ongoing biodiversity research and conservation efforts. In this context, we are inaugurating a new series of Data Papers under the AZORES BIOTA Biodiversity Data Journal Collection. These papers will systematically document and analyze previously unidentified specimens derived from multiple past expeditions aimed at surveying and monitoring a range of habitats across the Azores Islands. By integrating historical collections with modern research methodologies, this initiative aspires to reveal previously hidden facets of the archipelago's biodiversity and to inform future ecological, biogeographical and evolutionary studies, as well as conservation endeavours.

This first manuscript targets the subterranean arthropod fauna. Collected primarily during intensive field expeditions between 1991 and 2010, subterranean samples from the archipelago's diverse cave systems and mesovoid habitats form a vast assemblage of specimens — most of which remain unidentified — that illuminate the region's hidden and understudied biodiversity. Notably, the only taxonomically resolved subset comprises the cave-adapted ground‐beetles of the genus Trechus, a group of paramount importance to the understanding of the evolution of Azorean subterranean adapted fauna.

This study significantly contributes to addressing the Wallacean shortfall within the Azorean subterranean ecosystem by documenting novel range extensions for key endemic cave-adapted arthropods. Among the taxa recorded in previously uncharted locations are the centipede Lithobius obscurus azoreae Eason & Ashmole, 1992, the pseudoscorpion Pseudoblothrus vulcanus Mahnert, 1990, and several single-island endemic ground beetles of the genus Trechus, including Trechus terceiranus Machado, 1988 and Trechus picoensis Machado, 1988. These new distributional records enhance our understanding of species biogeography in the unique subterranean volcanic systems of the Azores and provide valuable insights into the connectivity and dispersal potential of troglobitic species in oceanic island settings.

Furthermore, this research plays a crucial role in defining new priority areas for the conservation of Azorean cave-adapted arthropods. By refining knowledge on species distributions, it supports the development of targeted spatial conservation strategies aimed at mitigating habitat degradation and preserving the fragile subterranean biodiversity of the archipelago. The findings of this study contribute directly to future conservation planning, ensuring that appropriate protective measures are implemented to safeguard these highly specialized and often vulnerable cave ecosystems.