To avoid sampling bias, they restricted their analysis to one group of animals—the bivalve molluscs—that fossilise well.

为了防止取样的偏颇，他们将分析的对象限制在一类化石记录保存完备动——类软体动。

When the Thompson quadruplets espied him one day, they called him a bivalve and ran quickly away.

有一天，汤普森家的四胞胎看见他， “贝！”

Unlike other molluscs, bivalves lack a radula and feature labial palps, which carry food from the gills to the mouth.

与其他软体动不同的是,贝缺乏齿舌,具有唇瓣,可将食由鳃送到口部.