Architecture of haptoral musculature in three species of Ligophorus (Monogenea, Ancyrocephalidae)

Abstract

The posterior attachment organs of monogeneans known as haptors show exceptional morphological plasticity and play a major role in monogenean taxonomy. Our knowledge of haptoral musculature, however, is still very limited and further study of this musculature in different groups of monogeneans may be instrumental in improving their taxonomic system and furthering our knowledge of their modes of attachment. This study used phalloidin staining in conjunction with confocal microscopy to examine haptoral musculature in three species of Ligophorus (L. llewelyni Dmitrieva et al., 2007, L. pilengas Sarabeev et Balbuena, 2004 and L. kaohsianghsieni (Gusev, 1962) Gusev, 1985), a member of the monopisthocotylean family Ancyrocephalidae sensu Bychovsky et Nagibina, 1978. Sclerotised structures (anchors, connecting bars and marginal hooks) were visualised simultaneously with muscles by capturing laser light reflected off the surfaces of these sclerites. The haptoral musculature was shown to be identical in L. pilengas and L. llewelyni and essentially similar between these two species and L. kaohsianghsieni, but the latter species had also some notable differences. Common to all three species were thick extrinsic muscles arising from the inner roots of the anchors, a muscle bundle connecting the inner roots of the opposite ventral anchors, muscles running from the outer roots of the anchors to the body wall, muscles originating from the dorsal bar and inserting on the anchoral openings and muscles connecting the bars with anchoral roots. Ligophorus llewelyni and L. pilengas have a more elaborate haptoral musculature than L. kaohsianghsieni with some additional muscles, tendon-like muscle extensions and a strong bracket-shaped muscle presumably functioning as a catch-muscle for the dorsal anchors. Functional roles of individual haptoral muscles in attachment are discussed and the architecture of haptoral musculature in Ligophorus is compared with that of other ancyrocephalids.