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.

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We would like to thank the technicians of the Rudolf Barth Electron Microscopy Platform of the Oswaldo Cruz Foundation, Rio de Janeiro, Brazil, for their help and access at the electron microscopes.


This study was supported by grants-in-aid and fellowship from Fundação de Amparo à Pesquisa do Rio de Janeiro ( (AMI, grant number 26/202.945/2016); fellowships from Conselho Nacional de Desenvolvimento Científico e Tecnológico ( (AMI, grant number 307932/2014-1 and 312934/2017-3) (JRMS, grant number 470724/2014-5); grants-in-aid and fellowships from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior ( (AMI and VHB, grant number 23038000059/2015-61) and grants-in-aid and fellowships from the COFECUB research and cooperation program ( (AMI and VHB, grant number 33387UA).

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Correspondence to Alena Mayo Iñiguez.

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Borba, V., Enoki, M., Lopes-Torres, E.J. et al. New data on eggshell structure of capillariid species: a SEM perspective. Parasitol Res 120, 963–970 (2021).

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  • Scanning electron microscopy
  • Capillariidae
  • Taxonomy
  • Eggshell ornamentation