Mode of attachment of a polyopisthocotylean parasite, Metamicrocotyla cephalusto the gills of Mugil cephalus through the study of haptoral compartments

ABSTRACT

The monogenean parasite, Metamicrocotyla cephalus uses the ventrally located haptor provided with two symmetrical rows of clamps in its attachment to the middle regions of the gill filaments of Mugil cephalus. Several factors are reported that protect the parasite from dislodgement by the breathing water current of the host. Firstly, the body of adult parasite produces 45 degrees with the longitudinal axis of the gill filament and its length is nearly equal to the free distal region of the filament located anterior to the site of attachment. So, the parasite did not bend to loop around the gill filaments as exhibited in mature ones with bodies longer than the gill filaments. Secondly, clamps can tightly grip two successive secondary gill lamellae in alternate positions which are directed inwardly towards the longitudinal axis of the haptor. Thirdly, the number of clamps depends on the age of the parasite where it increases as the age increases. Fourthly, the middle clamps are the largest while the anterior ones are the smallest. Fifthly, there is an exocytotic movement of electron-dense secretory bodies through the thin syncytium in the interior surface of the clamp. Sixthly, the clamp sclerites are embedded into the radial muscle fibers and directly inserted into the sclerite walls especially the median ones. Seventhly, the lateroposterior sclerite II is able to penetrate the gill tissue with its tip under the controlled action of three groups of muscle fibers. Thus, the protrusion and retraction of clamp are controlled by longitudinal haptoral muscle strands and extrinsic muscle fibers forming a highly organized array inside the haptor