Traditional methods for studying the morphology of microturbellarian flatworms rely on light microscopy, which often lacks the resolution necessary to capture fine structural details. Therefore, we present a protocol to improve the visualisation of structural morphological details in microturbellarians by means of scanning electron microscopy (SEM). We demonstrate this method by imaging the sclerotised copulatory organs of three species of Trigonostomum (Rhabdocoela, Trigonostomidae): T. venenosum, T. setigerum, and T. penicillatum. Additionally, we successfully visualise the bursal appendage of T. penicillatum. SEM imaging offered new morphological insights for the genus, and corrected earlier interpretations made with light microscopy. The method requires precision and careful handling, especially during the isolation of the hard parts. However, it is cost-effective and straightforward to carry out in any standard laboratory setting. Hence, our SEM protocol complements traditional light microscopy and opens new avenues for taxonomical research in microturbellarian taxa with hard parts.
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Clinostomum is a genus of parasitic trematodes found worldwide, infecting a wide range of hosts, including freshwater fishes, snails, birds and occasionally humans. In this study, clinostomid metacercariae were collected from Nile tilapia raised in fish farms in the Upper Tana River region, Kenya. The prevalence of infection was 17.2%, with metacercariae infecting the skin, gills and buccal cavity of the fish. Using light microscopy, scanning electron microscopy (SEM) and molecular methods targeting both nuclear ribosomal (ITS1, 5.8S, ITS2) and mitochondrial (COI) regions, the metacercariae were identified as C. cutaneum, C. phalacrocoracis, C. tilapiae and Euclinostomum heterostomum. The three species of Clinostomum have previously been reported to infect fish or piscivorous birds in Kenya, while this is the first report of E. heterostomum in this country. SEM analysis revealed new ultrastructural features of C. cutaneum, including an excretory pore surrounded by minute spiny papillae, an everted cirrus and dome-shaped papillae on the tegumental area around the genital pore. The cirrus lacked basal papillae, showing morphological variation between the adult and metacercarial stages. Our study, therefore, provides new insights into the phenotypic identification of flukes that may be pathogenic to fishes and humans and, therefore, of scientific and practical importance.
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