New data on eggshell structure of capillariid species: a SEM perspective

Capillariidae is a group of nematode parasites of vertebrates with a complex taxonomy. The structure of the eggshell, which was indicated as the most important characteristic for identification of genus or species through eggs, is very diverse among genera. The visualization and characterization of eggshell by light microscopy (LM) are a challenging task since different planes of the egg surface are needed. Nevertheless, categories of eggshell ornamentation were proposed by LM: smooth, punctuated, reticulated type I, and reticulated type II. The present study aimed to characterize the eggshell structure of Capillariidae species, parasites of mammals and avians, deposited in a helminthological collection using scanning electron microscopy (SEM). Institutional Biological Collections are taxonomic repositories of specimens described and strictly identified at the species level by systematics specialists. SEM eggshell images were obtained from 12 species belonging to 5 genera (Aonchotheca, Baruscapillaria, Capillaria, Echinocoleus, Eucoleus) and compared to their respective LM images. Eggshell patterns observed using SEM were associated categories of eggshell ornamentation previously proposed by LM images. The SEM data indicate that eggshell categories are not in agreement with capillariid genera or sites of infection. However, the study provides previously unknown SEM eggshell information from curated species, which contributes with a specific and supplementary taxonomic feature at the species level of Capillariidae.