Abdomen not annulate nor prolonged behind; eight legs in the adult stage.
Thus vertebrate and annulate embryos agree in certain points at the time of the formation of the primitive streak.
In eggs with yolk, whether vertebrate or annulate, there is always a separation into an animal and a plastic layer.
The longitudinal type characterises such genera as Vibrio, Filaria, Gordius, and all the annulate animals.
Cross rings may or may not be present, and the cup is either smooth or annulate.