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Spermiogenesis and spermatozoon ultrastructure of the caryophyllidean cestode Breviscolex orientalis Kulakovskaya, 1962, first member of the family Capingentidae studied, a parasite of cyprinid fish Abbottina rivularis, are described using transmission electron microscopy. Spermiogenesis in B. orientalis follows the Type II pattern described by Bâ and Marchand (Mém Mus Natl Hist Nat 166:87-95, 1995) for cestodes. It begins with the formation of a zone of differentiation containing a large nucleus and a pair of centrioles. The centrioles are separated from one another by an intercentriolar body composed of three electron-dense layers. Each centriole is associated with typical striated roots. At the beginning of the spermiogenesis, an electron-dense material is observed in the apical region of the differentiation zone. During the initial stage of spermiogenesis, one of the centrioles gives rise to a free flagellum, which then rotates and undergoes proximodistal fusion with the cytoplasmic protrusion of the differentiation zone. The mature spermatozoon of B. orientalis corresponds to the Type III pattern described by Levron et al. (Biol Rev 85:523-543, 2010). It is characterized by the absence of mitochondrion and crested body. Five regions of the mature spermatozoon are differentiated. The main ultrastructural characteristics are: one axoneme of 9+ "1" trepaxonematan pattern, cortical microtubules and nucleus. The comparison of the spermiogenesis of B. orientalis with those of the other caryophyllidean species demonstrates some variation within the order relative to the presence and morphology of the intercentriolar body, the presence of slight rotation of the flagellar bud and a complete proximodistal fusion of the free flagellum with a cytoplasmic protrusion.

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This paper reports results of the first cytogenetic study carried out on a recently described monozoic tapeworm, Khawia saurogobii Xi et al., 2009, from the Chinese lizard gudgeon (Saurogobio dabryi). The karyotype of this species is composed of eight pairs of metacentric and telocentric chromosomes (2n = 16; n = 3m + 5t), metacentric chromosomes representing the first, sixth, and eight pairs. All chromosomes except the largest pair displayed 4',6-diamidino-2-phenylidole (DAPI) positive heterochromatin in centromeric regions. In mitotic preparations stained with Giemsa, one of the homologues of a smaller metacentric chromosome pair (No. 7) showed a distinct secondary constriction, whereas the other did not. Fluorescent in situ hybridization (FISH) with 18S ribosomal DNA (rDNA) probe revealed that the chromosomes No. 7 carry each a cluster of ribosomal genes associated with the centromeric heterochromatin and confirmed that this chromosome pair contains a nucleolar organizer region (NOR). The rDNA-FISH also confirmed heteromorphism in the size of NOR (i.e., secondary constriction) observed after Giemsa staining. The present cytogenetic analysis revealed species-specific characters of K. saurogobii and showed that FISH may represent a new valuable cytogenetic tool suitable for comparative taxonomic or phylogenetic studies within the order Caryophyllidea in the future.

Chromosomal characteristics, i.e., number, size, morphology, and location of ribosomal DNA (rDNA) clusters were examined in two medically important liver flukes, Fasciola hepatica and Fascioloides magna (Fasciolidae), using conventional Giemsa staining and fluorescent in situ hybridization (FISH) with ribosomal 18S rDNA probe. A comparison of F. magna and F. hepatica karyotypes confirmed significant differences in all chromosomal features. Whilst the karyotype of F. hepatica comprised ten pairs of chromosomes (one metacentric and nine medium-sized subtelocentrics and submetacentrics; 2n = 20, n = 1 m + 5 sm + 4 st; TCL = 49.9 μm), the complement of F. magna was composed of 11 pairs of medium-sized subtelocentrics and submeta-metacentrics (2n = 22, n = 9 st + 1 sm + 1 sm-m; TCL = 35.2 μm). Noticeable differences were found mainly in length and morphology of first chromosome pair. It was metacentric and 9.0 μm long in F. hepatica while subtelocentric and 4.7 μm long in F. magna. Although FISH with rDNA probe revealed a single cluster of ribosomal genes in both species, conspicuous interspecific differences were displayed by chromosomal location of ribosomal loci (i.e., NORs). The signals were found on short arms of fifth homologous pair in F. hepatica; however, they were detected in pericentromeric regions of the long arms of tenth pair in F. magna. The observed cytogenetic differences were interpreted in terms of karyotype evolution of fasciolid flukes; F. hepatica may be regarded phylogenetically younger than F. magna. The present paper provides a pilot study on molecular cytogenetics within a group of hermaphroditic digenetic flukes.

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