Arthropod biodiversity is being investigated in the Carmanah Valley on Vancouver Island, British Columbia, Canada. We explore features related to the Centinelan extinction concept and ask whether or not this is applicable to northern temperate old-growth forest arthropods. Habitat loss in these forest systems is well documented and at present, of 89 old-growth forest watersheds over 5000 ha in size, only 6 remain intact. Examination of identified species (1,311 to date) from the intact old-growth forest of the Carmanah Valley indicates that this structurally complex habitat acts as a reservoir for biological diversity. Thirty species of oribatid mites and 8 species of staphylinid beetles are new to science and all of these species show habitat specificity to micro-habitats found within this old-growth forest. Nowhere is this more apparent than in the moss-mats of the high-canopy, where the oribatid mite fauna is composed of 56 species, of which 15 undescribed species are canopy specific. This mite assemblage forms a major component of a discrete arboreal community. Comparisons between the high-canopy and ground sites indicate that an additional 15 undescribed oribatid species are confined to the forest interior. No new species of oribatid mites or staphylinid beetles have been recorded in the forest edge or clear-cut sites. Evidence suggests microhabitats present in these old-growth forests contain an undescribed resident arthropod fauna. Without proper documentation, this faunal component is a candidate for the Centinelan extinction concept -- extinction of species unknown before their demise and hence unrecorded.