What Are the Similarities Between Annelids and Arthropods?

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Annelids and arthropods are similar in that they are both relatively small invertebrate animals with strong and obvious body segmentation, circulatory systems and a one-way gut. Scientists think annelids and arthropods share a common ancestor, or even that annelids are the ancestors of arthropods since there are species such as velvet worms that appear intermediate between them. Unfortunately, the fossil record for annelids is very poor.