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Embryogenesis and the first-stage larva of Thelazia lacrymalis

Published online by Cambridge University Press:  12 April 2024

H. Dongus ,
P. Beelitz  and
H. Schöl
H. Dongus
Affiliation:
Institute for Comparative Tropical Medicine and Parasitology, University of Munich, Leopoldstr. 5, D-80802 Munich, Germany
P. Beelitz*
Affiliation:
Institute for Comparative Tropical Medicine and Parasitology, University of Munich, Leopoldstr. 5, D-80802 Munich, Germany
H. Schöl
Affiliation:
Institute for Comparative Tropical Medicine and Parasitology, University of Munich, Leopoldstr. 5, D-80802 Munich, Germany
*
*Author for correspondence Fax: +49.89.2180 3623 E-mail: Pamela.Beelitz@tropa.vetmed.uni-muenchen.de
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Abstract

The female reproductive system of Thelazia lacrymalis (Nematoda: Thelaziidae) was investigated by light and scanning electron microscopy (SEM) with regard to the developmental stages and the stage deposited by the gravid nematode. Female T. lacrymalis have a didelphic and opisthodelphic type of reproductive system with paired ovaries, oviducts and uteri and a single vagina and vulva. Round and spindle-shaped primary oocytes are documented within the ovaries and oviducts, respectively. The distal part of each uterus provides a fertilization chamber filled with spermatozoa, followed by a sphincter-like part. Further anterior, the uteri broaden gradually containing dividing zygotes, small and large morulae, tadpole-stage embryos and horseshoe-shaped embryos which increase in length and become slimmer forming pretzel-stage embryos and larvae rolled up. The larvae stretch gradually and finally lie straight but still covered with their egg membrane in the vagina. The egg membrane encloses the whole larva and is enlarged at the pointed tail of the larva forming a bulb. At the SEM level, the first-stage larva is shown to have a terminal mouth and three hooks directed posteriorly and a striated cuticle. As morphologically identical larvae were also found in lavages of the conjunctival sac of horses infected with T. lacrymalis, this nematode species can be described as ovoviviparous.

Type
Review Article
Information
Journal of Helminthology , Volume 77 , Issue 3 , September 2003 , pp. 227 - 233
Copyright
Copyright © Cambridge University Press 2003

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