Smirnov P.A.1, Dobrovolskij A.A.† 2019. What is hidden under an eggshell? Ultrastructural evidence on morphology of “passive” Prosorhynchus squamatus miracidium (Digenea: Bucephalidae) // Invertebrate Zoology. Vol.16. No.4: 361–376 [in English].

1 Saint-Petersburg State University, Department of Invertebrate Zoology, Universitetskaya emb., 7/ 9, Saint- Petersburg, 199034, Russia. E-mail:

doi: 10.15298/invertzool.16.4.04

ABSTRACT: Miracidium is the larva of digeneans that serves to infect mollusks (first intermediate hosts). Many digeneans possess miracidia that use active strategy of infection. These larvae swim by ciliary action to the specific mollusks and penetrate into them. Miracidia of other digeneans follow an essentially different, passive way of infection: they rest in the eggshells and the mollusks become infected only after they ingest the eggs with larvae inside. The differences in strategies of infection are reflected in contrasting morphologies of the two types of miracidia. “Passive” ones are always smaller and “simplified”. However, very little is known about details behind this reduction. This is due to the evident lack of ulstrastructural data on “passive” forms. Here we present the TEM-reconstruction of P. squamatus “passive” miracidium and compare it with the well-known structure of “active” forms.

KEY WORDS: Digenea, Trematoda, Bucephalidae, miracidium, larva, passive strategy of infection, reduction, miniaturization.

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