Sponges are simple metazoans that build hierarchical mineral-organic architectures under ambient conditions, offering bioinspiration for lightweight, damage-tolerant structural materials. Yet the multiscale mechanics of freshwater sponges remain unexplored compared with well-studied marine species. Here we report the first quantitative investigation of an Amazonian freshwater sponge (Cauxi), linking its biogenic silica spicules and a double-shell, spicule-reinforced gemmule capsule to survival under alternating aquatic and subaerial conditions. Multiscale structural characterization combined with micro-/nanomechanical testing reveals that the silica spicules in Cauxi exhibit lower stiffness and toughness than fused glass, consistent with their amorphous, nanoporous structure. Micropillar tests show no statistically significant orientation dependence within experimental uncertainty, reflecting the spicules’ amorphous character. The gemmule architecture—two shells separated by a lightweight foam and reinforced by short spicules with star-like outer tips and disk-like inner bases—resists localized loading and suggests shell-buckling and rib-stiffening as operative protection principles. Building on these observations, we provide simple scaling arguments and testable predictions for buoyancy, dispersal by damage tolerance, positioning Cauxi as a model for lightweight, damage-tolerant capsules and short-fiber-reinforced composites formed under ambient conditions. These results articulate environment-specific structure–property trade-offs and offer generalizable cues for architected structural materials.
Materials Today , 2026, 95 103281.