有些种类的蜗牛有着从里到外逆时针的螺壳，不过这少见的多。
Some species of snail have shells that spiral out in an anticlockwise direction, but it is much rarer.
为了找到答案，研究人员对它们以及其他潜在亲属的DNA进行排序。 他们发现漂浮泡泡蜗牛是寄生于珊瑚和海葵的底栖蜗牛“梯螺”的后裔。
They discovered that the rafting snails are descendents of sea-floor snails that parasitize corals and sea anemones.
他决定把它们当成旋螺或蜗牛进行形态分析，试着导出它们在时间上的系谱史。
And he has decided to treat them as if they were tribolites, or snails, and to do a morphological analysis, and try to derive their genealogical history over time.
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