The Strongyloidea


The order Strongylida includes many of the important nematodes found in the gastrointestinal tracts of ruminants, horses, and swine, as well as the lungworms of ruminants and the hookworms of dogs and cats. The following table gives an overview of the classification of this order with an emphasis on the superfamily Strongyloidea.

Order Superfamily Family Subfamily Genus
- examples
Strongylida Trichostrongyloidea Trichostrongylidae
Strongyloidea Strongylidae Strongylinae Strongylus
Cyathostominae Cyathostomum
Chabertiidae Chabertiinae Chabertia
Oesophagostominae Oesophagostomum
Syngamidae Stephanurinae Stephanurus
Syngaminae Syngamus
Ancylostomatoidea Ancylostomatidae
Metastrongyloidea Metastrongylidae

















Their distinguishing features include a copulatory bursa (in males) and a buccal capsule of variable shape and size. Examples of direct (free living larvae) and indirect (intermediate host) life cycles can be found among the members of this order.

There are four superfamilies of importance in domestic animals:

  • Trichostrongyloidea
  • Strongyloidea
  • Ancylostomatoidea
  • Metastrongyloidea


Females belonging to the superfamilies Trichostrongyloidea, Strongyloidea and Ancylostomatoidea produce smooth,  thin-shelled, ellipsoidal "strongyle-type" eggs (A), approximately 80-100 microns long and 40-50 microns wide. One exception to this rule is Nematodirus, whose species produce eggs that are approximately twice the size of "strongyle-type eggs (B). Notice the difference between these eggs and the whipworm (Trichuris) egg (C).

A fifth (minor) superfamily, the Diaphanocephaloidea, are bursate nematodes found in the digestive tracts of terrestrial snakes and occasionally lizards. There are two genera and thirty three species in this superfamily. Females pass a "strongyle-type" egg and their life cycles are direct and similar to the Trichostrongyloidea but it is also believed that paratenic hosts (snails and slugs) may play a role in their life cycles.

Rbtn_nex.gif (1502 bytes) Rbtn_cont.gif (1897 bytes) Rbtn_top.gif (1435 bytes)


Parasites and Parasitic Diseases of Domestic Animals
Dr. Colin Johnstone (principal author)
Copyright 1998 University of Pennsylvania
This page was last modified on January 24, 2000