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[[Image:Trichuris ovis sheep.jpg|thumb|right|150px|''Trichuris ovis'' from sheep faeces - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]]

[[Image:Trichuris ovis sheep.jpg|thumb|right|150px|''Trichuris ovis'' from sheep faeces - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]]

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.