A re-examination of the haptoral sclerites forming the clamps, or ‘armoured suckers’, in Diclidophoroidea shows that they can be grouped into four main types, representing lines of evolution from what is here regarded as the primitive, or more generalized, form of clamp, that of the family Mazocraeidae. It has been shown that the form of the clamp skeleton must be regarded as of primary importance in the classification of the superfamily, since not only is it correlated with certain diagnostic characters of the soft parts of these worms, but it is usually fully developed some time before these parts make their appearance. Due attention has not always been paid to the detail of the clamps in systematic works, so that the position of some forms must remain uncertain until they can be redescribed. Owing to the sclerites often being twisted bars, curving through three dimensions, with the primary bars often jointed or fused, the appearance of different types of clamp is at first sight highly complex. The difficulty of interpreting them is increased by their being semi-transparent, and appearing of different shapes when viewed from various angles. These obscurities disappear when they are regarded as modifications of the fundamental plan found in Mazocraës and its allies.