| The inner and outer tube surfaces are very smooth, without any indication of segmentation, annulation, or collaring. |
| Pair rule, polarity and gap genes are present, but seem to have little or no role in segmentation. |
| Most nematodes, also called roundworms, are small, simple worms lacking the segmentation of the more familiar earthworms. |
| Infraoptic course of anterior cerebral arteries associated with abnormal gyral segmentation. |
| As adults they lack appendages, segmentation, and all internal organs except gonads and the remains of the nervous system. |
| A third level of population segmentation, representing more futuristic recommendations, is genetic profiling. |
