Integrative redescription of Sprostoniella micrancyra Cezar, Luque and Amato, 1999 (Monopisthocotylea: Capsalidae) and the phylogenetic position of Sprostoniella Bychowsky and Nagibina, 1967

Acta Parasitologica (2026) 71:124 https://doi.org/10.1007/s11686-026-01289-y ORIGINAL ARTICLE Integrative redescription of Sprostoniella micrancyra Cezar, Luque and Amato, 1999 (Monopisthocotylea: Capsalidae) and the phylogenetic position of Sprostoniella Bychowsky and Nagibina, 1967 Arthur Bessi Machado1 · Raquel de Oliveira Simões2 Marcos Antonio José dos Santos5 · José Luis Luque2 · Jhon Darly Chero3 · Arnaldo Maldonado Junior4 · Received: 8 January 2026 / Accepted: 13 April 2026 © The Author(s) 2026 Abstract Purpose The present study provides an integrative redescription of Sprostoniella micrancyra Cezar, Luque and Amato, 1999 (Monopisthocotylea: Capsalidae), a parasite of the Atlantic spadefish, Chaetodipterus faber (Broussonet, 1782) (Actinopterygii: Ephippidae) off the southeastern Brazilian coast. An additional specimen of Sprostoniella lamothei Pérez-Ponce de Léon and Mendoza-Garfias, 2000 collected from Parapsettus panamensis (Steindachner, 1876) in Peru was included for comparative molecular assessments. Methods S. micrancyra specimens were examined using light microscopy, histology, and scanning electron microscopy, with morphological preparations carried out following standard processing protocols. Genomic DNA was extracted from both Sprostoniella species, and partial sequences of the 28S rDNA and mitochondrial cox1 genes were generated. Phylogenetic relationships were inferred using Maximum Likelihood and Bayesian inference. Results Morphological observations of S. micrancyra revealed several previously unreported features, including the presence of a pair of accessory haptoral sclerites, a pair of anchors, a haptor with one central loculus, and the absence of a vaginal opening, contrasting with the original description. Scanning electron microscopy confirmed haptoral organization and detailed the structure of adhesive discs and peduncle musculature, while histology elucidated the organization of reproductive and attachment structures and muscular systems. Phylogenetic analyses of ribosomal and mitochondrial markers recovered the two Sprostoniella species as a monophyletic clade. Conclusion Our results expand current knowledge of S. micrancyra and underscore the importance of integrative approaches to clarify the taxonomy and evolutionary relationships of capsalids. Keywords Atlantic spadefish · Gill parasites · Ultrastructure · Molecular markers · Phylogenetic analysis · Capsalidae José Luis Luque 1 Programa de Pós-Graduação em Biologia Animal, Universidade Federal Rural do Rio de Janeiro, Seropédica, Brazil 2 Departamento de Parasitologia Animal, Universidade Federal Rural do Rio de Janeiro, Seropédica, Brazil 3 Laboratorio de Zoología de Invertebrados, Universidad Nacional Mayor de San Marcos, Lima, Peru 4 Laboratório de Biologia e Parasitologia de Mamíferos Silvestres Reservatórios, Fundação Instituto Oswaldo Cruz, Rio de Janeiro, Brazil 5 Departamento de Biologia Animal, Universidade Federal Rural do Rio de Janeiro, Seropédica, Brazil Introduction The genus Sprostoniella Bychowsky and Nagibina, 1967 (Capsalidae) currently comprises three recognized species, namely, its type species Sprostoniella multitestis Bychowsky and Nagibina, 1967; Sprostoniella micrancyra Cezar, Luque and Amato, 1999; and Sprostoniella lamothei Pérez-Ponce de León and Mendoza-Garfias, 2000 [1, 2]. These capsalids parasitize ephippid fishes of the genera Chaetodipterus Lacepède, 1802, Platax Cuvier, 1816 and Parapsettus Steindachner, 1876 in both Atlantic and IndoPacific oceans [2–8]. The genus is primarily characterized by a haptor with 17 peripheral loculi, a pair of accessory 124 Page 2 of 12 Acta Parasitologica (2026) 71:124 sclerites, a pair of submarginal anchors, two juxtaposed fields of multiple testes, and absence of a vagina [2, 3]. The species S. micrancyra was originally described from the Atlantic spadefish, Chaetodipterus faber (Broussonet, 1782) (Actinopterygii: Ephippidae), collected off the southeastern coast of Brazil [5]. This host, the only Atlantic representative of the family Ephippidae, is widely distributed from southern Brazil to the northeastern United States [9]. This parasitic species is characterized by the arrangement of septa and loculi in haptor, and relative size of the first anchor pair [5]. To date, C. faber remains the only known host for this parasite. Capsalids are of particular interest because several species are important pathogens of fish, especially in aquaculture [10]. Nevertheless, detailed histological studies of capsalids are scarce and have typically focused on host pathology rather than parasite anatomy [11–14]. In this study, S. micrancyra is redescribed based on newly collected specimens of C. faber collected off the coast of Rio de Janeiro, southeastern Brazil, using a combination of morphological, SEM, histological and molecular analyses. Furthermore, we investigate the phylogenetic position of Sprostoniella spp. within the Capsalidae based on analyses of partial 28S rDNA and cox1 sequences. single specimen of S. lamothei was found. This individual was divided, with the haptoral region mounted in Hoyer’s medium for morphological analysis of sclerotized structures, while the remaining portion was preserved in absolute ethanol for molecular analyses. Materials and methods Microscopy and illustrations Host and parasite collection Slides were examined and photographed under an Olympus BX51 microscope using Capture 2.4 software. Line drawings were prepared in Inkscape. Measurements are in micrometers, with ranges followed by means in parentheses. Voucher specimens of S. micrancyra (paragenophores, in whole-mounted and histological slides) and of S. lamothei (hologenophore, in Hoyer’s medium slide) were deposited in the Helminthological Collection of the Oswaldo Cruz Institute (CHIOC), Rio de Janeiro (Brazil), and in the Helminthological Collection of the Museum of Natural History at the San Marcos University (MUSM-HEL), Lima (Peru). Twenty specimens of C. faber and one specimen of the Panama spadefish, Parapsettus panamensis (Steindachner, 1876) (Actinopterygii: Ephippidae) were obtained from artisanal fishermen at local markets, respectively, in Rio de Janeiro State, southeastern Brazil, during July and August 2024, and in Lambayeque, northern Peruvian coast, during September 2025. Fish were identified according to Menezes and Figueiredo [9] and Chirichigno and Vélez [15], respectively. Gills were excised, rinsed over a 150 µm mesh sieve, and examined under a stereomicroscope for parasite detection. Parasites were detached from the gill using a fine brush and small-gauge needles. Morphological preparation Parasite specimens were preserved in 4% formalin, Bouin’s fluid, or absolute ethanol depending on subsequent analyses. Specimens of S. micrancyra (n = 24) were stained with hydrochloric carmine [16], cleared with clove oil, and mounted in Canada balsam. One specimen of S. micrancyra was prepared w (...truncated)