Velocity distributions in 30–38.5 km s⁻¹ (panel a), 38.5–42 km s⁻¹ (panel b), and 42–44 km s⁻¹ (panel c), respectively. The points are coloured with the velocity values shown in the right colour bar. The asterisks represent the MSF clumps, ‘▽’ mark the YSO clumps, ‘△’ flag the protostellar clumps, and the squares are for the quiescent clumps. The black lines denote the spines of the filaments hf1, hf2, and hf3. The clumps are coded with different colours in the W33 complex (yellow) and in the filaments (red), respectively.