| We thought that leeches were one group and their sister group with the oligochaetes, earthworms and a variety of other aquatic annelids. |
| Many annelids and molluscs share patterns of development in early embryonic stages. |
| Although mollusks, annelids, brachiopods, and sipunculans are closely related, the relationships between them are not well resolved. |
| This is in contrast to organisms such as annelids and arthropods, in which the main nerve cord is ventral. |
| The oligochaetes include earthworms and a group of related, mostly freshwater, species of annelids. |
| In the complementary category, the protostomes, which includes annelids and arthropods, the blastopore develops into the mouth. |
