One strain designated W2.09-231^T was isolated from an aquifer through a 150-metre-deep borehole feeding a mineral-water bottling plant in Central Portugal. Based on 16S rRNA gene sequence analysis, the novel organism is most closely related to the species of the genera Perlucidibaca and Paraperlucidibaca, belonging to the family Moraxellaceae, with 16S rRNA gene pairwise sequence similarity of 94.5 and 93.1 %, respectively. The strain was not pigmented and formed Gram-stain-negative, non-motile, short rod-shaped cells. The organism was strictly aerobic, and oxidase- and catalase-positive. Strain W2.09-231^T was organotrophic, but grew only on a very limited number of single carbon sources. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and one major unknown phospholipid. Ubiquinone 12 (U-12) was the major respiratory quinone. The DNA G+C content of strain W2.09-231^T was 62.0 mol%. Based on phylogenetic, physiological and biochemical characteristics, we describe a novel species of a novel genus represented by strain W2.09-231^T ( = CECT 8582^T = LMG 28332^T) for which we propose the name Cavicella subterranea gen. nov., sp. nov. We also propose to emend the description of the species Perlucidibaca piscinae to reflect new results obtained in this study.