Comparative ultrastructure study of lamellar gastrodermal projections in Echinostoma paraensei, E-caproni, and E. trivolvis (Trematoda: Echinostomatidae)

A comparative ultrastructure study using transmission electron microscopy (TEM) of ultrathin sections, freeze-fracture replication, and scanning electron microscopy (SEM) was conducted on the gastrodermal lamellar microvilli in adults of Echinostoma paraensei, E. caproni, and E. trivolvis. Lamellar projections observed by SEM were mainly planiform and rhomboidal or paddle-shaped, and they were commonly seen in the three species. The distal margins of these lamellae were mainly smooth in E. paraensei, whereas filiform or digitiform extensions in the margins occurred occasionally in E. caproni and frequently in E. trivolvis. Freeze-fracture TEM elucidated significant interspecific differences in the numbers of intramembranous particles (IMP) per square micrometer; the numbers of IMP were significantly lower in E. trivolvis than in either E. caproni or E. paraensei. Thus, ultrastructural differences in the gastrodermal lamellae of adult echinostomes will be a taxonomically useful criterion for distinguishing species of Echinostoma.