Morpho-functional specialization of the branching sporocyst of Prosorhynchoides borealis Bartoli, Gibson & Bray, 2006 (Digenea, Bucephalidae)

Abstract

Sporocysts of Prosorhynchoides borealis were obtained from the marine bivalves Abra prismatica and studied using transmission electron microscopy. The sporocyst body consists of a mass of branching and intertwining hollow tubules that ramify through the host's digestive gland and gonads. This study investigated the ultrastructure of the sporocyst branches which comprise alternate distended areas (brood chambers) with a relatively thin body wall, narrower portions with a thicker body wall (constricted areas) and terminal regions. Pronounced differences between these areas were revealed in the structure of their tegument and body cavity lining, as well as in the cellular composition of the subtegumental layers. Body wall composition in distended areas was consistent with the specialization for cercarial nurture in the brood chambers. The structure of the constrictions suggested a dual role of nutrient absorption and physical separation of adjacent brood chambers. Two types of terminal region were identified, one specialized for the investigation and penetration of host tissues and the other, in which the germinal cells are formed, for cercarial production. The overall structure of the sporocyst branches helps explain why this linear modular system, i.e. brood chambers and constrictions continuously growing into the host tissue, enables the sporocyst's long-term existence and can continuously produce cercariae in numbers comparable with those produced by rediae and/or daughter sporocyst infrapopulations in other digeneans. The origin of the nuclei in the outer tegumental layer of some branching bucephalid sporocysts is also discussed.

The fine structure of the germinal mass, brood cavity and birth canal of the rediae of the monoxenous hemiuroid digeneanBunocotyle progeneticaChabaud & Buttner, 1959

“…Electron microscopy studies have shown that the rediae of B. progenetica differ from the rediae of T. anatis and H. elongata in the presence of the cellular lining around their brood cavity. In earlier ultrastructural studies (Reader, 1975; Russell-Pinto et al ., 1996; Klag et al ., 1997; Podvyaznaya & Galaktionov, 2012), similar specialized cells lining the brood cavity have been described in daughter sporocysts of Cercaria helvetica XII , Meiogymnophallus minutus , Diplostomum pseudospathaceum and in bucephalid sporocysts of P. borealis . It is notable that the lining of the brood cavity in digenean parthenitae often has characters that make it similar to an epithelial layer.…”

“…It is notable that the lining of the brood cavity in digenean parthenitae often has characters that make it similar to an epithelial layer. For instance, in bucephalids the lining of the brood cavity is underlain (on the side of the sporocyst body wall) by a distinct basal lamina (Podvyaznaya & Galaktionov, 2012). In B. progenetica , the luminal surface of this lining bears lamellar projections, which are common in the digenean epithelia.…”

Microanatomy and ultrastructure of the nervous system of adult Renicola parvicaudatus (Digenea: Renicolidae)

“…In contrast, monociliated sensory papillae in adults show greater diversity at the ultrastructural level, namely through rootlet morphology, shape of nerve bulb, number of dense collars, and especially through the abundance of vesicles in the neuroplasm. The identified components of the free ciliated sensory papillae in adult R. parvicaudatus are also characteristic of simple monociliated sensory endings described for various digeneans at different life cycle stages (Antonelli et al, 2014; Czubaj & Niewiadomska, 1988, 1996; Dixon & Mercer, 1965; Dunn et al, 1987; Pan, 1980; Poddubnaya, Zhokhov, & Gibson, 2020; Podvyaznaya & Galaktionov, 2012; Silk & Spence, 1969; Tihomirov, 2000; Wilson, 1970; Žd’árská & Nebesářová, 2003), as well as for other representatives of the Neodermata group (e.g., Biserova et al, 2016; Lyons, 1973; Rohde, 1989, 1990). The arrangement of cytoskeletal structures is probably of decisive importance for the mechanoreceptive function of sensory bulbs, for example those identified in the S 2 acetabular group in maritae and cercariae of R. parvicaudatus (present study; Denisova & Shchenkov, 2020b).…”

“…The parasitic lifestyle significantly affects the organization and functional role of the nervous system, which is of great importance for the transmission of these parasites. Many studies provide data on the cytomorphology of the central (CNS) and peripheral (PNS) nervous systems of digeneans of various taxa (e.g., Born‐Torrijos et al, 2017; Czubaj & Niewiadomska, 1990, 1996; Denisova et al, 2023; Dunn et al, 1987; Leksomboon et al, 2012; Podvyaznaya & Galaktionov, 2012; Poddubnaya, Zhokhov & Gibson, 2020; Rees, 1975; Tihomirov, 2000; Žd’árská & Nebesářová, 2003). Most of these studies relate to the individual stage of the life cycle, which prevents the determination of structural changes in the nervous tissue through ontogenesis.…”

“…The most complete data on the cytomorphology of the nervous system were previously obtained for Schistosoma mansoni Sambon, 1907 (Schistosomatidae) (Cousin & Dorsey, 1991; Dorsey et al, 2002; Marks et al, 1995; Pan, 1980; Reissig, 1970; Silk & Spence, 1969) and Fasciola hepatica Linnaeus, 1758 (Fasciolidae) (Brownlee et al, 1994; Dixon & Mercer, 1965; Gresson & Threadgold, 1964; Sukhdeo & Sukhdeo, 1994; Sukhdeo et al, 1988; Wilson, 1970). The organization of trematode cerebral ganglia and neurons shares many ultrastructural similarities with those of free‐living Platyhelminthes (for review, see Halton & Gustafsson, 1996); their neurons exhibit neurosecretory activity and determine neuronal control of growth and development (Fairweather & Halton, 1991; Gresson & Threadgold, 1964; Harris & Cheng, 1972; Podvyaznaya & Galaktionov, 2012; Stewart et al, 2003). Some species show specific ultrastructural features of the nervous system, e.g.…”