Relationship between the specific star formation rate and the total stellar mass (left), the stellar mass surface density (centre), and the metallicity (right) for HI-normal (HI - def ≤ 0.4; filled dots) and HI-deficient (HI - def > 0.4; empty circles) galaxies. The large filled blue dots indicate the mean values for each morphological class for normal gas-rich systems and the empty red ones for cluster HI-deficient galaxies. For the large symbols the error bar shows the standard deviation of the distribution. The dotted line shows the bisector fit determined for HI-normal galaxies. The small error bar shows the typical uncertainty on the data.