Spermiogenesis and spermatozoon ultrastructure in basal polyopisthocotylean monogeneans, Hexabothriidae and Chimaericolidae, and their significance for the phylogeny of the Monogenea

Abstract

Sperm ultrastructure provides morphological characters useful for understanding phylogeny; no study was available for two basal branches of the Polyopisthocotylea, the Chimaericolidea and Diclybothriidea. We describe here spermiogenesis and sperm in Chimaericola leptogaster (Chimaericolidae) and Rajonchocotyle emarginata (Hexabothriidae), and sperm in Callorhynchocotyle callorhynchi (Hexabothriidae). Spermiogenesis in C. leptogaster and R. emarginata shows the usual pattern of most Polyopisthocotylea with typical zones of differentiation and proximo-distal fusion of the flagella. In all three species, the structure of the spermatozoon is biflagellate, with two incorporated trepaxonematan 9 + “1” axonemes and a posterior nucleus. However, unexpected structures were also seen. An alleged synapomorphy of the Polyopisthocotylea is the presence of a continuous row of longitudinal microtubules in the nuclear region. The sperm of C. leptogaster has a posterior part with a single axoneme, and the part with the nucleus is devoid of the continuous row of microtubules. The spermatozoon of R. emarginata has an anterior region with membrane ornamentation, and posterior lateral microtubules are absent. The spermatozoon of C. callorhynchi has transverse sections with only dorsal and ventral microtubules, and its posterior part shows flat sections containing a single axoneme and the nucleus. These findings have important implications for phylogeny and for the definition of synapomorphies in the Neodermata. We point out a series of discrepancies between actual data and interpretation of character states in the matrix of a phylogeny of the Monogenea. Our main conclusion is that the synapomorphy “lateral microtubules in the principal region of the spermatozoon” does not define the Polyopisthocotylea but is restricted to the Mazocraeidea.

Spermatological Characterization of the Cestode Meggittina gerbilli (Cyclophyllidea: Catenotaeniidae), a Parasite of Gerbils, Gerbillus gerbillus and Gerbillus campestris (Rodentia: Muridae) in Tunisia

“…Ultrastructural studies on spermiogenesis and the spermatozoon have been demonstrated as a useful source of characters for phylogenetic inference in diverse parasitic groups of Platyhelminthes [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. In the case of cestodes, Świderski [ 16 ] described three models of spermiogenesis, namely the pseudophyllidean type, the caryophyllidean type, and the cyclophyllidean type, which were based on the number of flagella/axonemes that originated from the differentiation zone and the presence/absence of the flagella proximodistal fusion.…”

A Review of Sperm Ultrastructural Characters in the Opecoelidae (Digenea) and Their Phylogenetic Implications, with New Data on Peracreadium characis, a Parasite of Diplodus puntazzo in Tunisia

“…Combining multiple sources of information (morphological characters, molecular data, life cycle and the ultrastructural organization of male gametes) would allow for more robust phylogenetic inferences. In the case of the Opistholebetinae, the organization of sperm cells of representatives of this subfamily might provide additional information to clarify the systematic status and phylogenetic relationships within opecoelids, as demonstrated in other parasitic Platyhelminthes, especially monogeneans and cestodes [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. Sperm ultrastructure has already been described for twelve opecoelid species distributed over five subfamilies.…”

Ultrastructure of mature spermatozoa of three Bucephalidae (Prosorhynchus longisaccatus, Rhipidocotyle khaliliandBucephalus margaritae) and phylogenetic implications

“…Today, ultrastructural studies of the mature spermatozoon of Platyhelminthes have provided useful characters for the understanding of phylogenetic relationships between Platyhelminthes [1, 9, 12]. In the Bucephalidae, ultrastructural data on the mature spermatozoon exist for four species belonging to three genera, namely the bucephalines Prosorhynchoides arcuatus [10], Prosorhynchoides gracilescens published as Bucephaloides gracilescens [5], Pseudorhipidocotyle elopichthys [26] and the prosorhynchine Prosorhynchus aculeatus [14].…”