ULTRASTRUCTURE OF THE SURFACE-STRUCTURES OF ALLODISCOCOTYLA-DIACANTHI(POLYOPISTHOCOTYLEA, MONOGENEA) FROM THE GILLS OF THE MARINE TELEOST FISH, SCOMBEROIDES-TOL

Scanning and transmission electron microscopic studies have been made of the surface architecture of the fish-gill parasite, Allodiscocotyla diacanthi, Observations of the haptor region have revealed the presen ce of cushion-like supports at the base of each clamp, together with a pair of anchor-hooks. Other topographical features observed included a mid-ventrally positioned genital atrium and a ventrolateral vaginal pore. Tegumental serrations, composed of electron-dense bars, partiall y cover the hindbody, and their presence may serve in the adhesive att itude of the worm, in response to the flow of displacement water curre nts. The tegumental syncytium contains numerous dense granules and luc ent vesicles, the contents of which are released into the cytosol of t he syncytium. The clamp sclerites are invested with tegument which, in some specimens, contained inclusions resembling bacteria. Groups of n eurons containing characteristic dense-cored vesicles were observed fr equently in the clamp region. Each jaw of the clamp is distinguished b y the presence of approximately 175 non-ciliated putative sensory endi ngs, and a pair of cone-like sensillae occurs on the ventral surface o f the lappet, Additionally, the entire body surface of the worm is cov ered with some 3000-4000 unicilated structures that are presumed to be sensory in nature.