The common feature of members of this group is that the oesophagus is a column of doughnut-shaped cells. They are only distantly related to the other nematode groups and so drugs developed primarily for controlling strongyle and ascarid worms are often less effective against these. | The common feature of members of this group is that the oesophagus is a column of doughnut-shaped cells. They are only distantly related to the other nematode groups and so drugs developed primarily for controlling strongyle and ascarid worms are often less effective against these. |