Morphology and diagnosis of the fourth-stage larva of Coronocyclus labratus (Looss, 1900) (Nematoda: Strongyloidea) parasitising equids.

This research article explains the identification and description of the fourth-stage larva of a common equid parasite, Coronocyclus labratus, by noting specific characteristics compared to corresponding stages of other similar parasites.

Identification and Description of the Parasite

• The fourth-stage larva (L4) of Coronocyclus labratus, a common species found in equids such as horses and donkeys, is identified and described in this study.
• The identified larvae were confirmed to be of C. labratus through the detection of moulting forms. These forms exhibited unique characters of both larval and adult stages, facilitating the confirmation.
• Despite resembling the larvae of other species such as Cylicocyclus leptostomum, Cyathostomum catinatum, and Cylicostephanus goldi, the L4 of C. labratus had distinguishable features.

Comparison with Other Species

• The buccal capsule (BC), a part of the digestive system in the larvae, has a thinner wall in Cylicocyclus leptostomum than in C. labratus. The ring of the oesophageal funnel, another digestive structure, is also less developed in the former.
• Coronocyclus labratus has a dorsal tooth that protrudes only slight into the buccal cavity. The larva also possesses an elongate, pyriform-shaped oesophagus, characteristic to the species.
• In contrast, the BC walls are thicker in Cyathostomum catinatum, and the dorsal tooth is more bluntly pointed. If present, the sublateral teeth in C. catinatum are bluntly pointed, compared to their usual absence or indistinct presence in C. labratus.
• The larvae of Cylicostephanus goldi can be differentiated from those of C. labratus because of the larger size of their BC.

Implications of the Study

• The study provides critical insights necessary for the accurate identification and differentiation of the fourth larval stage of these closely related equid parasites. The detailed description and comparison of their distinct anatomical features enhance our understanding of their developmental stages, which is crucial in studying their life cycle, impacts on host species, and potential for control or treatment strategies.