Section 16A. The clerk of the superior court for criminal business in Suffolk county may designate, with the approval of the chief justice of the trial court, 1 assistant clerk appointed under section 5, as the unified session clerk to perform, under the direction of the clerk of the superior court for criminal business in Suffolk county, duties pertaining to the statewide unified session for trials and hearings relative to the determination of sexually dangerous persons pursuant to section 9 of chapter 123A. Such clerk shall receive, in addition to the salary paid to an assistant clerk under section 4, a sum equivalent to 10 per cent of the salary of an assistant clerk.