Haptoral neuromusculature in two species of Dactylogyrus Diesing, 1850 (Monogenea: Dactylogyridae).

The taxonomy of Dactylogyrus Diesing, 1850 (Monogenea: Dactylogyridae), like that of most monopisthocotyleans, relies heavily on the morphology of sclerites of the posterior attachment organ (haptor). However, the associated neuromusculature is essentially unknown and, therefore, the aim of this study was to use confocal microscopy to examine the haptoral neuromusculature in two species of Dactylogyrus: D. amphibothrium Wagener, 1857 and D. crucifer Wagener, 1857. The monogeneans were stained with phalloidin for muscle and with antibodies for FMRFamide and 5HT and confocal reflectance microscopy was used to visualise the sclerites (i.e. anchors, marginal hooks and bars). Both species had a similar architecture of the anchoral musculature, with a pair of extrinsic muscles, two interconnecting muscles and muscles attached to the haptoral wall, anchoral openings and a connecting bar. The musculature of most marginal hooks consisted of retractors and protractors inserted on the proximal ends of the hooks. The two species differed significantly in the musculature of the accessory ventral bar: D. crucifer had a four-rayed bar with an elaborate musculature associated with the marginal hooks and D. amphibothrium had a rod-shaped bar with simple musculature. Patterns of neurotransmitter immunoreactivity (IR) in the haptor were similar in both species: RFamide-IR cells were clustered in a pair of pre-anchoral ganglia interconnected by a neurite bundle, 5HT-IR cells formed a ventral loop projecting neurites to the marginal hooks. The functional roles of haptoral muscles and patterns of neurotransmitters are discussed. In D. crucifer, the confocal reflectance microscopy revealed an additional sclerite (accessory dorsal bar) that had never been described previously in this or any other species of Dactylogyrus, suggesting that the reflected-light technique might be useful in identifying sclerites undetectable by conventional methods.