Asymmetries in the attachment apparatus of a gill parasite

Diplozoids are fish ectoparasites with a direct life cycle. Adults live attached to fish gills, using two haptors with four pairs of clamps for attachment. Three planes of symmetry (the individual, haptor and clamp planes) can be identified in adult diplozoids. In this study, the haptor and clamp planes of symmetry are used to study different asymmetries (fluctuating asymmetry FA, directional asymmetry DA, antisymmetry) in the attachment apparatus of Paradiplozoon homoion(Diplozoidae; Monogenea). DA and antisymmetry may be adaptive asymmetries, whereas FA (measured as the random deviation from perfect symmetry in bilateral characters) is suggested as a useful tool for estimating developmental instability. Fifty individuals of P. homoion were collected from 25 gudgeon Gobio gobio. Asymmetries were estimated for nine morphometric traits in the haptor plane and three morphometric traits in the clamp plane on all four pairs of clamps from each individual. FA did not differ between traits on the individual pairs of clamps. However, significant DA was detected for most traits in the clamp plane.