Question

Why would Phylum Annelida and Phylum Arthropoda be grouped together. What characteristic(s) unite these phyla? Why does DNA evidence group them into separate clades?

Answer 1

Both Phyla Annelids and Arthropods have segmented body and are mostly dioecious (having distinct reproductive system in different individuals). However, initial studies have united both of these phylas based on segmentation as segmentation was considered to be critical part of classification.

There are several differences between the two phylas. Annelids have closed circulatory system like human whereas arthropods have an open circulatory system. Obtaining the 18s and 28s r DNA sequence of both these phylas led to the fact that both these groups, are individualistically different and should be separated into different clades. Expression and positioning of many genes that leads to specific function are also different in both of these phylas has also separated them into different clades