<br> The second manuscript in the series 'Dalberto Teixeira Pombo (DTP) Arthropod Collection' focuses on Algar do Carvão, a remarkable volcanic pit on Terceira Island, Azores, that is a Natural Monument, a show cave and part of the Terceira Island Natural Park. This volcanic cave is unique amongst the archipelago’s subterranean systems due to its distinctive geological features, including rare silica-based speleothems and its exceptional natural setting. Surrounded by remnants of native laurel forest, the cave hosts a specialised assemblage of arthropods, including several taxa endemic to the Azores and single island endemic species. Of particular interest are four obligate cave-dwelling species or subspecies (troglobionts): the centipede<br> Lithobius obscurus azoreae<br> Eason & Ashmole, 1992 (Chilopoda, Lithobiomorpha, Lithobiidae); the springtail<br> Pseudosinella ashmoleorum<br> da Gama, 1988 (Collembola, Entomobryomorpha, Entomobryidae); the spider<br> Turinyphia cavernicola<br> Wunderlich, 2008 (Arachnida, Araneae, Linyphiidae); and the ground beetle<br> Trechus terceiranus<br> Machado, 1988 (Insecta, Coleoptera, Carabidae), the last two being endemics to Terceira Island. These species are part of a fragile and narrowly distributed subterranean fauna shaped by the volcanic origin of the island and its isolation (0.4 Ma). Their presence highlights the conservation value of Algar do Carvão, which serves not only as a cave biodiversity hotspot, but also as a natural laboratory for studying evolution, adaptation to subterranean habitats and island biogeography. Despite being a show cave with frequent human visits, Algar do Carvão retains a relatively intact hypogean ecosystem, though it remains vulnerable to anthropogenic pressures, such as habitat disturbance and pollution.<br> <br> <br> Particular focus is given to the abundance and population trends of the endemic cave-adapted beetle<br> Trechus terceiranus<br> , monitored through a long-term standardised programme initiated in 1999 using non-lethal trapping methods. This effort, designed to monitor population variation across seasons and years and to evaluate the potential impacts of increasing human visitation to the cave, represents one of the few continuous monitoring programmes for cave arthropods on oceanic islands. Over the course of this study, we also report the first citation of 21 arthropod taxa for Algar do Carvão, two of which are endemic to the Azores (<br> Canariphantes acoreensis<br> (Wunderlich, 1992) and<br> Phloeostiba azorica<br> (Fauvel, 1900)), contributing significantly to the known biodiversity of this volcanic pit, in particular and of Azorean subterranean fauna, in general.<br>
