Ultrastructure of an opecoelid daughter sporocyst, Podocotyle sp. (Digenea: Opecoelidae): comparative analysis of the somatic tissues and new insights into the organization of the nervous system

Abstract

Digenea is a group of widespread parasitic flatworms with a complex life cycle including a successive change of parthenogenetic and hermaphroditic generations. Daughter sporocysts are among the least studied parthenitae in terms of the ultrastructure of their body wall and nervous system. Here we present an ultrastructural and immunocytochemical study of <i>Podocotyle</i> sp. daughter sporocyst (Opecoelidae), parasitizing in <i>Littorina obtusata</i> Linnaeus, 1758 from the White Sea. Our results focus on the structure of the body wall, birth pore, excretory and nervous systems, and include new data on the taxonomic affiliation based on the partial cox1 mtDNA sequence. The daughter sporocyst of <i>Podocotyle</i> sp. has ultrastructural similarities with different plagiorchiid and diplostomid digeneans and also possesses some specific features. In the studied species, the birth canal is epithelialized; the body wall is composed of nine types of somatic cells and includes a well-developed central nervous system. Neurons of the latter form specific hemidesmosome-like attachment sites, which we found in digeneans for the first time. The obtained results are necessary to complement the comparative morphological analysis of daughter parthenogenetic generations in different digenean lineages.

Molecular and morphological screening of Podocotyle spp. (Trematoda: Opecoelidae) sheds light on their diversity in Northwest Pacific and eastern European Arctic

“…3)) appeared as a poorly supported sister clade to Podocotyle sp. of Denisova et al (2023) (ex Littorina obtusata (Linnaeus, 1758)), and all of them together also formed a poorly supported sister clade to Podocotyle sp. 2.…”

“…Intramolluscan stages of Podocotyle sp. of Denisova et al (2023) and P. atomon of Sokolov et al (2019), parasitizing Littorina spp., are a particular taxonomic problem. Their belonging to the genus Podocotyle is undoubted (Novotný 2019; this study), but the species affiliation remains enigmatic.…”

“…At present, molecular data are available only for sporocysts and/or cercariae of Podocotyle sp. of Denisova et al (2023) and Podocotyle atomon of Sokolov et al (2019) and adults Podocotyle cf. atomon of Denisova et al (2023) and Podocotyle scorpaenae (Rudolphi, 1819) (Denisova et al 2023;Jousson et al 1999;Sokolov et al 2019).…”

“…of Denisova et al (2023) and Podocotyle atomon of Sokolov et al (2019) and adults Podocotyle cf. atomon of Denisova et al (2023) and Podocotyle scorpaenae (Rudolphi, 1819) (Denisova et al 2023;Jousson et al 1999;Sokolov et al 2019). However, data on the genetic marker most appropriate for reliable DNA barcoding, namely the cox1 mtDNA gene, were obtained only for Podocotyle sp.…”

“…However, data on the genetic marker most appropriate for reliable DNA barcoding, namely the cox1 mtDNA gene, were obtained only for Podocotyle sp. of Denisova et al (2023) ex Littorina obtusata (Linnaeus, 1758) and Podocotyle cf. atomon of Denisova et al (2023) ex Cyclopterus lumpus Linnaeus, 1758.…”