Comparative study of the three attachment mechanisms of diplectanid monogeneans

Abstract

One of the main characteristics of the monogenean family Diplectanidae Monticelli, 1903 is their complex haptor formed by 2 pairs of hooks, transversal bars, 14 peripheral marginal hooks, and accessory adhesive organ (lamellodisc or squamodisc) that can be present or absent. Sub-family Lamellodiscinae Oliver, 1969 presents one or two lamellodiscs, formed by several overlapped lamellar esclerites (lamellae) which are piled up. Species like Furnestina echeneis only have one large ventral lamellodisc. This organ function has been categorized in different ways (i.e. accessory adhesive organ, supplementary or compensating disc or sucker), although its real mode of operation and function is still unclear. Specimens of Lamellodiscus and F. echeneis were examined. The lamellodisc of F. echeneis, studied both in vivo and fixed, seems to work as a sucker: the separated lamellae revolve around the single smallest lamellodisc lamella like the slats of a hand-held fan and create a suction volume. Lamellodiscus spp. lamellae (except the basal one) slide in telescopic movement, exerting a posterior and ventral or dorsal force that tightens it to the secondary gill lamellae. This force is contrary to the pulling force of hooks. Opposite forces together with the attachment to two different secondary gill lamellae gives strong binding and stability. These observations were compared with previous knowledge about Diplectanum aequans of subfamily Diplectaninae Monticelli, 1903, whose squamodiscs are formed by numerous spines and presents a different attach strategy. D. aequans produces extensive and deep alterations in the gill epithelium surrounding the parasite. The different attachment mechanisms of the diplectanid species can explain the different degrees of damage that each species provoke, and the information provided in this work can be useful for anthelmintic treatment designs.