Ultrastructural characteristics of the uterine epithelium of aspidogastrean and digenean trematodes

Abstract

The ultrastructure of the uterus proper of the aspidogastrean Aspidogaster limacoides Diesing, 1835 and two digenean species, Phyllodistomum angulatum Linstow, 1907 (Plagiorchiida, Gorgoderidae) and Azygia lucii (Müller, 1776) (Strigeida, Azygiidae), was examined by transmission electron microscopy (TEM). The uterine epithelial lining of these species is thin, except for the perinuclear region of the epithelial cells. Septate junctions occur between adjacent epithelial cells within the uterine wall. The luminal surface of the cells is elevated into microlamellae, which project into the uterine lumen and cover the entire epithelial lining. Basally the uterine epithelium is attached to a basal matrix, and its supporting layers of muscle fibres are weak and composed of scattered circular muscles. Despite the marked similarity in the ultrastructural pattern of the aspidogastrean and two digeneans studied, there is some degree of variation in the secretory activity of their uterine epithelium. The high level of vesicular exocytotic activity in the epithelial cytoplasm of A. lucii may be associated with differences in egg emission and the subsequent life cycle involving a non-ciliated, non-swimming and non-free-living miracidium, as opposed to the free-swimming miracidium of P. angulatum. The similar nature of the uterine epithelium in all three species studied represents an ultrastructural marker possibly supporting a close phylogenetic relationship between the Aspidogastrea and the Digenea.

Advanced stages of embryonic development and cotylocidial morphogenesis in the intrauterine eggs of Aspidogaster limacoides Diesing, 1835 (Aspidogastrea), with comments on their phylogenetic implications

“…Although the posterior sucker (incipient ventral disc) of the cotylocidium initially resembles the ventral/posterior sucker of digeneans, it subsequently undergoes subdivision into numerous alveoli. Our TEM studies tend to support the early ideas of Burmeister (1856), Monticelli (1892), Furhmann (1928), Faust (1932), Faust and Tang (1936), Chauhan (1954) and Dollfus (1958) for treating the Aspidogastrea as a separate group occupying an intermediate position between the Monogenea and the Digenea (Timofeeva 1975(Timofeeva , 2005Poddubnaya et al 2011Poddubnaya et al , 2012. Rohde (1972) also indicated that the Aspidogastrea seem to combine features of both monogeneans and digeneans.…”