A mesophilic, facultative, anaerobic, xylanolytic-cellulolytic bacterium, $TW1^T$, was isolated from sludge in an anaerobic digester fed with pineapple waste. Cells stained Gram-positive, were spore-forming, and had the morphology of straight to slightly curved rods. Growth was observed in the temperature range of 30 to $50^{circ}C$ (optimum $37^{circ}C$) and the pH range of 6.0 to 7.5 (optimum pH 7.0) under aerobic and anaerobic conditions. The strain contained meso-diaminopimelic acid in the cell-wall peptidoglycan. The predominant isoprenoid quinone was menaquinone with seven isoprene units (MK-7). Anteiso-$C_{15:0}$, iso-$C_{16:0}$, anteiso-$C_{17:0}$, and $C_{16:0}$ were the predominant cellular fatty acids. The G+C content of the DNA was 49.5 mol%. A phylogenetic analysis based on 16S rRNA showed that strain $TW1^T$ belonged within the genus Paenibacillus and was closely related to Paenibacillus cellulosilyticus LMG $22232^T$, P. curdlanolyticus KCTC $3759^T$, and P. kobensis KCTC $3761^T$ with 97.7, 97.5, and 97.3% sequence similarity, respectively. The DNA-DNA hybridization values between the isolate and type strains of P. cellulosilyticus LMG $22232^T$, P. curdlanolyticus KCTC $3759^T$, and P. kobensis KCTC $3761^T$ were found to be 18.6, 18.3, and 18.0%, respectively. The protein and xylanase patterns of strain $TW1^T$ were quite different from those of the type strains of closely related Paenibacillus species. On the basis of DNA-DNA relatedness and phenotypic analyses, phylogenetic data and the enzymatic pattern presented in this study, strain $TW1^T$ should be classified as a novel species of the genus Paenibacillus, for which the name Paenibacillus xylaniclasticus sp. nov. is proposed. The type strain is $TW1^T$ (=NBRC $106381^T$=KCTC $13719^T$=TISTR $1914^T$).